cssi/SciSciGPT-SciSciNet huggingface dataset:
Data-Driven Ambiguity Sets With Probabilistic Guarantees for Dynamic Processes

Distributional ambiguity sets provide quantifiable ways to characterize the uncertainty about the true probability distribution of random variables of interest. This makes them a key element in data-driven robust optimization by exploiting high-confidence guarantees to hedge against uncertainty. This article explores the construction of Wasserstein ambiguity sets in dynamic scenarios, where data are collected progressively and may only reveal partial information about the unknown random variable. For random variables evolving according to known dynamics, we leverage assimilated samples to make inferences about their unknown distribution at the end of the sampling horizon. Under exact knowledge of the flow map, we provide sufficient conditions that relate the growth of the trajectories with the sampling rate to establish a reduction of the ambiguity set size as the horizon increases. Furthermore, we characterize the exploitable sample history that results in a guaranteed reduction of ambiguity sets under errors in the computation of the flow and when the dynamics is subject to bounded unknown disturbances. Our treatment deals with both full- and partial-state measurements and, in the latter case, exploits the sampled-data observability properties of linear time-varying systems under irregular sampling. Simulations on an unmanned aerial vehicle detection application show the superior performance resulting from the proposed dynamic ambiguity sets.
Bi-fidelity stochastic gradient descent for structural optimization under uncertainty

The presence of uncertainty in material properties and geometry of a structure is ubiquitous. The design of robust engineering structures, therefore, needs to incorporate uncertainty in the optimization process. Stochastic gradient descent (SGD) method can alleviate the cost of optimization under uncertainty, which includes statistical moments of quantities of interest in the objective and constraints. However, the design may change considerably during the initial iterations of the optimization process which impedes the convergence of the traditional SGD method and its variants. In this paper, we present two SGD based algorithms, where the computational cost is reduced by employing a low-fidelity model in the optimization process. In the first algorithm, most of the stochastic gradient calculations are performed on the low-fidelity model and only a handful of gradients from the high-fidelity model is used per iteration, resulting in an improved convergence. In the second algorithm, we use gradients from the low-fidelity models to be used as control variate, a variance reduction technique, to reduce the variance in the search direction. These two bi-fidelity algorithms are illustrated first with a conceptual example. Then, the convergence of the proposed bi-fidelity algorithms is studied with two numerical examples of shape and topology optimization and compared to popular variants of the SGD method that do not use low-fidelity models. The results show that the proposed use of a bi-fidelity approach for the SGD method can improve the convergence. Two analytical proofs are also provided that show linear convergence of these two algorithms under appropriate assumptions.
PARP1 inhibitors trigger innate immunity via PARP1 trapping-induced DNA damage response

It is being increasingly appreciated that the immunomodulatory functions of PARP1 inhibitors (PARPi) underlie their clinical activities in various BRCA-mutated tumors. PARPi possess both PARP1 inhibition and PARP1 trapping activities. The relative contribution of these two mechanisms toward PARPi-induced innate immune signaling, however, is poorly understood. We find that the presence of the PARP1 protein with uncompromised DNA-binding activities is required for PARPi-induced innate immune response. The activation of cGAS-STING signaling induced by various PARPi closely depends on their PARP1 trapping activities. Finally, we show that a small molecule PARP1 degrader blocks the enzymatic activity of PARP1 without eliciting PARP1 trapping or cGAS-STING activation. Our findings thus identify PARP1 trapping as a major contributor of the immunomodulatory functions of PARPi. Although PARPi-induced innate immunity is highly desirable in human malignancies, the ability of 'non-trapping' PARP1 degraders to avoid the activation of innate immune response could be useful in non-oncological diseases.
Effects of mavacamten on Ca2+ sensitivity of contraction as sarcomere length varied in human myocardium.

Background and purpose Heart failure can reflect impaired contractile function at the myofilament level. In healthy hearts, myofilaments become more sensitive to Ca2+ as cells are stretched. This represents a fundamental property of the myocardium that contributes to the Frank-Starling response, although the molecular mechanisms underlying the effect remain unclear. Mavacamten, which binds to myosin, is under investigation as a potential therapy for heart disease. We investigated how mavacamten affects the sarcomere-length dependence of Ca2+ -sensitive isometric contraction to determine how mavacamten might modulate the Frank-Starling mechanism. Experimental approach Multicellular preparations from the left ventricular-free wall of hearts from organ donors were chemically permeabilized and Ca2+ activated in the presence or absence of 0.5-μM mavacamten at 1.9 or 2.3-μm sarcomere length (37°C). Isometric force and frequency-dependent viscoelastic myocardial stiffness measurements were made. Key results At both sarcomere lengths, mavacamten reduced maximal force and Ca2+ sensitivity of contraction. In the presence and absence of mavacamten, Ca2+ sensitivity of force increased as sarcomere length increased. This suggests that the length-dependent activation response was maintained in human myocardium, even though mavacamten reduced Ca2+ sensitivity. There were subtle effects of mavacamten reducing force values under relaxed conditions (pCa 8.0), as well as slowing myosin cross-bridge recruitment and speeding cross-bridge detachment under maximally activated conditions (pCa 4.5). Conclusion and implications Mavacamten did not eliminate sarcomere length-dependent increases in the Ca2+ sensitivity of contraction in myocardial strips from organ donors at physiological temperature. Drugs that modulate myofilament function may be useful therapies for cardiomyopathies.
Link Prediction through Deep Generative Model

Inferring missing links based on the currently observed network is known as link prediction, which has tremendous real-world applications in biomedicine, e-commerce, social media, and criminal intelligence. Numerous methods have been proposed to solve the link prediction problem. Yet, many of these methods are designed for undirected networks only and based on domain-specific heuristics. Here we developed a new link prediction method based on deep generative models, which does not rely on any domain-specific heuristic and works for general undirected or directed complex networks. Our key idea is to represent the adjacency matrix of a network as an image and then learn hierarchical feature representations of the image by training a deep generative model. Those features correspond to structural patterns in the network at different scales, from small subgraphs to mesoscopic communities. When applied to various real-world networks from different domains, our method shows overall superior performance against existing methods.
Electrical properties of thermal oxide scales on pure iron in liquid lead-bismuth eutectic

Abstract The impedance behavior of pre-oxidized iron in liquid lead-bismuth eutectic (LBE) at 200 °C is studied using electrochemical impedance spectroscopy. The structures and resistance of oxide grown on iron oxidized in air at different temperatures and durations are compared. The results show that the resistance of the oxide film increases with increasing oxidizing temperature, due to the formation of a thicker scale and fewer defects. At the same temperature (600 °C), increasing the oxidation time can also reduce the defect concentration in the oxide film and improve the impedance of the oxide scale in LBE.
Learning to Solve Large-Scale Security-Constrained Unit Commitment Problems

Security-constrained unit commitment (SCUC) is a fundamental problem in power systems and electricity markets. In practical settings, SCUC is repeatedly solved via mixed-integer linear programming ...
Predictors of diabetes risk perception among college students.

To explore the diabetes knowledge and future disease risk perception of college students. Participants: 697 college students were purposefully recruited at a large state university and completed an...
Revisit of AAA Excellence of Global Value Chains: Robustness, Resilience, and Realignment

What are the attributes of the best performing supply chains? According to Lee (2004), the best supply chains are agile, adaptable, and ensure the interests of all participating companies stay aligned, i.e., The Triple-A framework. Fifteen years later, we find global supply chains exposed, with an increasing frequency and alarming severity, to low probability disruptive shocks. We revisit the question of the current attributes of best performing supply chains in a highly uncertain and risk fraught world. Using the lessons of the last twenty years, we propose a new framework, the “Triple A & R” framework, as the foundational concept for defining excellence capabilities in global supply chains. Supply chains have to enhance agility with robustness, for real time excellent performance across a wide-range of risk scenarios. Adaptability has to go beyond adjustment to trends and require the building of resilience to recover from current shocks and proactively mitigate future such shocks. We need to rethink and pursue re-alignment of incentives for a “new normal” with changing consumer preferences, new value propositions and innovative business models. We review relevant literature that supported the implementation of Triple-A practices in the best chains, and highlight the challenges faced by them in the last twenty years. We offer an array of interesting research directions to flesh out “Triple A & R” concepts and develop practices for its effective implementation.
Exploration of lattice Hamiltonians for functional and structural discovery via Gaussian Process-based Exploration-Exploitation

Statistical physics models ranging from simple lattice to complex quantum Hamiltonians are one of the mainstays of modern physics that have allowed both decades of scientific discovery and provided a universal framework to understand a broad range of phenomena from alloying to frustrated and phase separated materials to quantum systems. Traditionally, exploration of the phase diagrams corresponding to multidimensional parameter spaces of Hamiltonians was performed using a combination of basic physical principles, analytical approximations, and extensive numerical modeling. However, exploration of complex multidimensional parameter spaces is subject to the classic dimensionality problem, and the behaviors of interest concentrated on low dimensional manifolds remain undiscovered. Here, we demonstrate that a combination of exploration and exploration–exploitation with Gaussian process modeling and Bayesian optimization allows effective exploration of the parameter space for lattice Hamiltonians and effectively maps the regions at which specific macroscopic functionalities or local structures are maximized. We argue that this approach is general and can be further extended well beyond the lattice Hamiltonians to effectively explore the parameter space of more complex off-lattice and dynamic models.
Polarizing Tweets on Climate Change.

We introduce a framework to analyzes the conversation between two competing groups of Twitter users, one who believe in the anthropogenic causes of climate change (Believers) and a second who are skeptical (Disbelievers). As a case study, we use Climate Change related tweets during the United Nation’s (UN) Climate Change Conference – COP24 (2018), Katowice, Poland. We find that both Disbelievers and Believers talk within their group more than with the other group; this is more so the case for Disbelievers than for Believers. The Disbeliever messages focused more on attacking those personalities that believe in the anthropogenic causes of climate change. On the other hand, Believer messages focused on calls to combat climate change. We find that in both Disbelievers and Believers bot-like accounts were equally active and that unlike Believers, Disbelievers get their news from a concentrated number of news sources.
Polarization modulation time-domain terahertz polarimetry.

We present high precision measurements of polarization rotations in the frequency range from 0.1 to 2.5 THz using a polarization modulation technique. A motorized stage rotates a polarizer at ∼ 80 Hz, and the resulting modulation of the polarization is measured by a lock-in technique. We achieve an accuracy of 0.050° (900 μrad) and a precision of 0.02° (350 μrad) for small rotation angles. A detailed mathematical description of the technique is presented, showing its ability to fully characterize elliptical polarizations from 0.1 to 2.5 THz.
Gamow Vectors in a Periodically Perturbed Quantum System

Gamow vectors and resonances play an important role in scattering theory, especially in the physics of metastable states. We study Gamow vectors and resonances in a time-dependent setting using the Borel summation method. In particular, we analyze the behavior of the wave function ψ(x,t) for one dimensional time-dependent Hamiltonian \(H=-\partial_{x}^{2}\pm2\delta(x)(1+2r\cos\omega t)\) where ψ(x,0) is compactly supported.
The isoperimetric problem in the plane with the sum of two Gaussian densities

We consider the isoperimetric problem for the sum of two Gaussian densities in the line and the plane. We prove that the double Gaussian isoperimetric regions in the line are rays and that if the double Gaussian isoperimetric regions in the plane are half-spaces, then they must be bounded by vertical lines.
A SIMPLE MODEL FOR QUASAR DEMOGRAPHICS

We present a simple model for the relationship between quasars, galaxies, and dark matter halos from 0.5 < z < 6. In the model, black hole (BH) mass is linearly related to galaxy mass, and galaxies are connected to dark matter halos via empirically constrained relations. A simple "scattered" light bulb model for quasars is adopted, wherein BHs shine at a fixed fraction of the Eddington luminosity during accretion episodes, and Eddington ratios are drawn from a lognormal distribution that is redshift independent. This model has two free, physically meaningful parameters at each redshift: the normalization of the M BH-M gal relation and the quasar duty cycle; these parameters are fit to the observed quasar luminosity function (LF) over the interval 0.5 < z < 6. This simple model provides an excellent fit to the LF at all epochs and also successfully predicts the observed projected two-point correlation of quasars from 0.5 < z < 2.5. It is significant that a single quasar duty cycle at each redshift is capable of reproducing the extant observations. The data are therefore consistent with a scenario wherein quasars are equally likely to exist in galaxies, and therefore dark matter halos, over a wide range in masses. The knee in the quasar LF is a reflection of the knee in the stellar-mass-halo-mass relation. Future constraints on the quasar LF and quasar clustering at high redshift will provide strong constraints on the model. In the model, the autocorrelation function of quasars becomes a strong function of luminosity only at the very highest luminosities and will be difficult to observe because such quasars are so rare. Cross-correlation techniques may provide useful constraints on the bias of such rare objects. The simplicity of the model allows for rapid generation of quasar mock catalogs from N-body simulations that match the observed LF and clustering to high redshift.
Microstructure Analysis of Bismuth Absorbers for Transition-Edge Sensor X-ray Microcalorimeters

Given its large X-ray stopping power and low specific heat capacity, bismuth (Bi) is a promising absorber material for X-ray microcalorimeters and has been used with transition-edge sensors (TESs) in the past. However, distinct X-ray spectral features have been observed in TESs with Bi absorbers deposited with different techniques. Evaporated Bi absorbers are widely reported to have non-Gaussian low-energy tails, while electroplated ones do not show this feature. In this study, we fabricated Bi absorbers with these two methods and performed microstructure analysis using scanning electron microscopy and X-ray diffraction microscopy. The two types of material showed the same crystallographic structure, but the grain size of the electroplated Bi was about 40 times larger than that of the evaporated Bi. This distinction in grain size is likely to be the cause of their different spectral responses.
A Note on Alternating Minimization Algorithm for the Matrix Completion Problem

We consider the problem of reconstructing a low-rank matrix from a subset of its entries and analyze two variants of the so-called alternating minimization algorithm, which has been proposed in the past. We establish that when the underlying matrix has rank one, has positive bounded entries, and the graph underlying the revealed entries has diameter which is logarithmic in the size of the matrix, both algorithms succeed in reconstructing the matrix approximately in polynomial time starting from an arbitrary initialization. We further provide simulation results which suggest that the second variant which is based on the message passing type updates performs significantly better.
Particle-in-cell simulations of shock-driven reconnection in relativistic striped winds

By means of two- and three-dimensional particle-in-cell simulations, we investigate the process of driven magnetic reconnection at the termination shock of relativistic striped flows. In pulsar winds and in magnetar-powered relativistic jets, the flow consists of stripes of alternating magnetic field polarity, separated by current sheets of hot plasma. At the wind termination shock, the flow compresses and the alternating fields annihilate by driven magnetic reconnection. Irrespective of the stripe wavelength ? or the wind magnetization ? (in the regime ????1 of magnetically dominated flows), shock-driven reconnection transfers all the magnetic energy of alternating fields to the particles, whose average Lorentz factor increases by a factor of ? with respect to the pre-shock value. In the limit ?/(rL?)???1, where rL is the relativistic Larmor radius in the wind, the post-shock particle spectrum approaches a flat power-law tail with slope around ?1.5, populated by particles accelerated by the reconnection electric field. The presence of a current-aligned ?guide? magnetic field suppresses the acceleration of particles only when the guide field is stronger than the alternating component. Our findings place important constraints on the models of non-thermal radiation from Pulsar Wind Nebulae and relativistic jets.
Local cut points and splittings of relatively hyperbolic groups

In this paper we show that the existence of a non-parabolic local cut point in the Bowditch boundary $\partial(G,\mathbb{P})$ of a relatively hyperbolic group $(G,\mathbb{P})$ implies that $G$ splits over a $2$-ended subgroup. This theorem generalizes a theorem of Bowditch from the setting of hyperbolic groups to relatively hyperbolic groups. As a consequence we are able to generalize a theorem of Kapovich and Kleiner by classifying the homeomorphism type of $1$-dimensional Bowditch boundaries of relatively hyperbolic groups which satisfy certain properties, such as no splittings over $2$-ended subgroups and no peripheral splittings. In order to prove the boundary classification result we require a notion of ends of a group which is more general than the standard notion. We show that if a finitely generated discrete group acts properly and cocompactly on two generalized Peano continua $X$ and $Y$, then $Ends(X)$ is homeomorphic to $Ends(Y)$. Thus we propose an alternate definition of $Ends(G)$ which increases the class of spaces on which $G$ can act.
Improving Performance in Quantum Mechanics with Explicit Incentives to Correct Mistakes.

Advanced physics students do not use their mistakes as an opportunity to learn unless given an explicit incentive to do so.
Energy Dissipation Through Quasi-static Tides in White Dwarf Binaries

We present a formalism to study tidal interactions in white dwarf binaries in the limiting case of quasi-static tides, in which the tidal forcing frequencies are small compared to the inverse of the white dwarf’s dynamical time scale. The formalism is valid for arbitrary orbital ecc entricities and therefore applicable to white dwarf binaries in the Galactic disk as well as globular clusters. I n the quasi-static limit, the total perturbation of the gravitational potential shows a phase shift with respect to the position of the companion, the magnitude of which is determined primarily by the efficiency of energy dissipat ion through convective damping. We determine rates of secular evolution of the orbital elements and white dwarf rotational angular velocity for a 0.3 M⊙ helium white dwarf in binaries with orbital frequencies in the Laser Interferometer Space Antenna (LISA) gravitational wave frequency band and companion masses ranging from 0.3 M⊙ to 10 5 M⊙. The resulting tidal evolution time scales for the orbital semi-major axis are longer than a Hubble time, so that convective damping of quasi-static tides need not be considered in the construction of gravitat ional wave templates of white dwarf binaries in the LISA band. Spin-up of the white dwarf, on the other hand, can occur on time scales of less than 10 Myr, provided that the white dwarf is initially rotating with a fr equency much smaller than the orbital frequency. For semi-detached white dwarf binaries spin-up can occur on time scales of less than 1 Myr. Nevertheless, the time scales remain longer than the orbital inspiral time sca les due to gravitational radiation, so that the degree of asynchronism in these binaries increases. As a consequence, tidal forcing eventually occurs at forcing frequencies beyond the quasi-static tide approximation. For the shortest period binaries, energy dissipation is therefore expected to take place through dynamic tides and resonantly excited g-modes. Subject headings:Stars: Binaries: Close, Stars: White Dwarfs, Stars: Oscill ations
Derivative-free optimization for parameter estimation in computational nuclear physics

We consider optimization problems that arise when estimating a set of unknown parameters from experimental data, particularly in the context of nuclear density functional theory. We examine the cost of not having derivatives of these functionals with respect to the parameters. We show that the POUNDERS code for local derivative-free optimization obtains consistent solutions on a variety of computationally expensive energy density functional calibration problems. We also provide a primer on the operation of the POUNDERS software in the Toolkit for advanced optimization.
Particle Physics in a Season of Change

A digest of the authors opening remarks at the 2011 Hadron Collider Physics Symposium. I have chosen my title to reflect the transitions we are living through, in particle physics overall and in hadron collider physics in particular. Data-taking has ended at the Tevatron, with {approx} 12 fb{sup -1} of {bar p}p interactions delivered to CDF and D0 at {radical}s = 1.96 TeV. The Large Hadron Collider has registered a spectacular first full-year run, with ATLAS and CMS seeing > 5 fb{sup -1}, LHCb recording {approx} 1 fb{sup -1}, and ALICE logging nearly 5 pb{sup -1} of pp data at {radical}s = 7 TeV, plus a healthy dose of Pb-Pb collisions. The transition to a new energy regime and new realms of instantaneous luminosity exceeding 3.5 x 10{sup 33} cm{sup -2} s{sup -1} has brought the advantage of enhanced physics reach and the challenge of pile-up reaching {approx} 15 interactions per beam crossing. I am happy to record that what the experiments have (not) found so far has roused some of my theoretical colleagues from years of complacency and stimulated them to think anew about what the TeV scale might hold. We theorists have had plenty of time to explore many proposals for electroweak symmetry breaking and for new physics that might lie beyond established knowledge. With so many different theoretical inventions in circulation, it is in the nature of things that most will be wrong. Keep in mind that we learn from what experiment tells us is not there, even if it is uncommon to throw a party for ruling something out. Some non-observations may be especially telling: the persistent absence of flavor-changing neutral currents, for example, seems to me more and more an important clue that we have not yet deciphered. It is natural that the search for the avatar of electroweak symmetry breaking preoccupies participants and spectators alike. But it is essential to conceive the physics opportunities before us in their full richness. I would advocate a three-fold approach: Explore, Search, Measure! The first phase of running at the LHC has brought us to two new lands - in proton-proton and lead-lead collisions - and we may well enter other new lands with each change of energy or increase of sensitivity. I believe that it will prove very rewarding to spend some time simply exploring each new landscape, without strong preconceptions, to learn what is there and, perhaps, to encounter interesting surprises. Directed searches, for which we have made extensive preparations, are of self-evident interest. Here the challenge will be to broaden the searches over time, so the searches are not too narrowly directed. Our very successful conception of particles and forces is highly idealized. We have a great opportunity to learn just how comprehensive is our network of understanding by making precise measurements and probing for weak spots, or finding more sweeping accord between theory and experiment.
Generalized Twisted Modules Associated to General Automorphisms of a Vertex Operator Algebra

We introduce a notion of a strongly \({\mathbb{C}^{\times}}\)-graded, or equivalently, \({\mathbb{C}/\mathbb{Z}}\)-graded generalized g-twisted V-module associated to an automorphism g, not necessarily of finite order, of a vertex operator algebra. We also introduce a notion of a strongly \({\mathbb{C}}\)-graded generalized g-twisted V-module if V admits an additional \({\mathbb{C}}\)-grading compatible with g. Let \({V=\coprod_{n\in \mathbb{Z}}V_{(n)}}\) be a vertex operator algebra such that \({V_{(0)}=\mathbb{C}\mathbf{1}}\) and V(n) = 0 for n < 0 and let u be an element of V of weight 1 such that L(1)u = 0. Then the exponential of \({2\pi \sqrt{-1}\; {\rm Res}_{x} Y(u, x)}\) is an automorphism gu of V. In this case, a strongly \({\mathbb{C}}\)-graded generalized gu-twisted V-module is constructed from a strongly \({\mathbb{C}}\)-graded generalized V-module with a compatible action of gu by modifying the vertex operator map for the generalized V-module using the exponential of the negative-power part of the vertex operator Y(u, x). In particular, we give examples of such generalized twisted modules associated to the exponentials of some screening operators on certain vertex operator algebras related to the triplet W-algebras. An important feature is that we have to work with generalized (twisted) V-modules which are doubly graded by the group \({\mathbb{C}/\mathbb{Z}}\) or \({\mathbb{C}}\) and by generalized eigenspaces (not just eigenspaces) for L(0), and the twisted vertex operators in general involve the logarithm of the formal variable.
Molecular dynamics simulations of a single stranded (ss) DNA

The objective of this study was to develop an understanding of short-single stranded DNA (ssDNA) to aid the development of new DNA-based biosensors. The various thermodynamic macroscopic observables (temperature and energy distributions) and root mean square deviation (RMSD) of nucleic acid backbone of 12 base-sequences of ssDNA of the P53 gene between 130 and 144 codon were studied using molecular dynamics (MD) simulations. The AMBER program was utilized to prepare the ssDNA structure of the p53 sequence and MD simulations were carried out using NAMD program. In this study, we compared the outcome of the properties of ssDNA system by different ensembles. The microcanonical ensemble (NVE) and conical ensemble (NVT) and isobaric—isothermal (NPT) ensemble were employed to characterize the equilibrium behavior of ssDNA in aqueous solution.
Fast Characterization of Dispersion and Dispersion Slope of Optical Fiber Links Using Spectral Interferometry With Frequency Combs

We demonstrate fast characterization ( ~ 1.4 ?s) of both the dispersion and dispersion slope of long optical fiber links ( ~ 25 km) using dual quadrature spectral interferometry with an optical frequency comb. Compared to previous spectral interferometry experiments limited to fiber lengths of meters, the long coherence length and the periodic delay properties of frequency combs, coupled with fast data acquisition, enable spectral interferometric characterization of fibers longer by several orders of magnitude. We expect that our method will be useful to recently proposed lightwave techniques like coherent wavelength-division multiplexing and to coherent modulation formats by providing a real-time monitoring capability for the link dispersion. Another area of application would be in stabilization of systems which perform frequency and timing distribution over long fiber links using stabilized optical frequency combs.
A note on Gauss?Bonnet holographic superconductors

We present an analytic treatment near the phase transition for the critical temperature of (3+1)-dimensional holographic superconductors in Einstein?Gauss?Bonnet gravity with backreaction. We find that the backreaction makes the critical temperature of the superconductor decrease and condensation harder. This is consistent with previous numerical results.Communicated by Misao Sasaki
A documentary of high-mass star formation: Probing the dynamical evolution of Orion Source I on 10–100 AU scales using SiO masers

A comprehensive picture of high-mass star formation has remained elusive, in part because examples of high-mass young stellar objects (YSOs) tend to be relatively distant, deeply embedded, and confused with other emission sources. These factors have impeded dynamical investigations within tens of AU of high-mass YSOs—scales that are critical for probing the interfaces where outflows from accretion disks are launched and collimated. Using observations of SiO masers obtained with the Very Large Array (VLA) and the Very Long Baseline Array (VLBA), the KaLYPSO project is overcoming these limitations by mapping the structure and dynamical/temporal evolution of the material 10-1000 AU from the nearest high-mass YSO: Radio Source I in the Orion BN/KL region. Our data include ~40 epochs of VLBA observations over a several-year period, allowing us to track the proper motions of individual SiO maser spots and to monitor changes in the physical conditions of the emitting material with time. Ultimately these data will provide 3-D maps of the outflow structure over approximately 30% of the outflow crossing time. Here we summarize recent results from the KaLYPSO project, including evidence that high-mass star formation occurs via disk-mediated accretion.
Recovery of eigenvectors from eigenvalues in systems of coupled harmonic oscillators

This paper uses the recently formulated eigenvalue-eigenvector identity to reveal the physics of globally coupled radio frequency oscillators. This identity allows for the estimation of eigenvectors from the eigenvalues of the system under study, plus the eigenvalues of a group of subsystems. The group of subsystems was created by successive removal and replacement of single oscillators. This finding is a proof-of-principle for the recovery of system parameters from general coupled oscillator systems.
Mirror maps, modular relations and hypergeometric series II

As a continuation of [1], we study modular properties of the periods, the mirror maps and Yukawa couplings for multi-moduli Calabi-Yau varieties. In Part A of this paper, motivated by the recent work of Kachru-Vafa, we degenerate a three-moduli family of Calabi-Yau toric varieties along a codimension one subfamily which can be described by the vanishing of certain Mori coordinate, corresponding to going to the “large volume limit” in a certain direction. Then we see that the deformation space of the subfamily is the same as a certain family of K3 toric surfaces. This family can in turn be studied by further degeneration along a subfamily which in the end is described by a family of elliptic curves. The periods of the K3 family (and hence the original Calabi-Yau family) can be described by the squares of the periods of the elliptic curves. The consequences include: (1) proofs of various conjectural formulas of physicists [2][3] involving mirror maps and modular functions; (2) new identities involving multi-variable hypergeometric series and modular functions — generalizing [1]. In Part B, we study for two-moduli families the perturbation series of the mirror map and the type A Yukawa couplings near certain large volume limits. Our main tool is a new class of polynomial PDEs associated with Fuchsian PDE systems. We derive the first few terms in the perturbation series. For the case of degree 12 hypersurfaces in P 4 [6,2,2,1,1], in one limit the series of the couplings are expressed in terms of the j function. In another limit, they are expressed in terms of rational functions. The latter give explicit formulas for infinite sequences of “instanton numbers” n d .
A new approach to hyperbolic inverse problems

We present a modification of the BC method in inverse hyperbolic problems. The main novelty is the study of the restrictions of the solutions to the characteristic surfaces instead of the fixed time hyperplanes. The main result is that the time-dependent Dirichlet-to-Neumann operator prescribed on a part of the boundary uniquely determines the coefficients of the self-adjoint hyperbolic operator up to a diffeomorphism and a gauge transformation. In this paper, we prove the crucial local step. The global step of the proof will be presented in a forthcoming paper.
The Chern–Ricci flow on complex surfaces

The Chern–Ricci flow is an evolution equation of Hermitian metrics by their Chern–Ricci form, first introduced by Gill. Building on our previous work, we investigate this flow on complex surfaces. We establish new estimates in the case of finite time non-collapsing, analogous to some known results for the Kahler–Ricci flow. This provides evidence that the Chern–Ricci flow carries out blow-downs of exceptional curves on non-minimal surfaces. We also describe explicit solutions to the Chern–Ricci flow for various non-Kahler surfaces. On Hopf surfaces and Inoue surfaces these solutions, appropriately normalized, collapse to a circle in the sense of Gromov–Hausdorff. For non-Kahler properly elliptic surfaces, our explicit solutions collapse to a Riemann surface. Finally, we define a Mabuchi energy functional for complex surfaces with vanishing first Bott–Chern class and show that it decreases along the Chern–Ricci flow.
ANALYTIC MODELING OF STARSHADES

External occulters, otherwise known as starshades, have been proposed as a solution to one of the highest priority yet technically vexing problems facing astrophysics—the direct imaging and characterization of terrestrial planets around other stars. New apodization functions, developed over the past few years, now enable starshades of just a few tens of meters diameter to occult central stars so efficiently that the orbiting exoplanets can be revealed and other high-contrast imaging challenges addressed. In this paper, an analytic approach to the analysis of these apodization functions is presented. It is used to develop a tolerance analysis suitable for use in designing practical starshades. The results provide a mathematical basis for understanding starshades and a quantitative approach to setting tolerances.
On squeezed limits in single-field inflation. Part I

The n-point correlation functions in single-field inflation obey a set of consistency conditions in the exact squeezed limit which are not present in multi-field models, and thus are powerful tools to distinguish between the two. However, these consistency conditions may be violated for a finite range of scales in single-field models, for example by departures from the Bunch-Davies state. These excited states may be the consequence of interactions during inflation, or may be a remnant of the era that preceded inflation. In this paper we analyze the bispectrum, and show that in the regime of theoretical control the resulting signal in the squeezed limit remains undetectably small in all known models which continuously excite the state. We also show that the signal remains undetectably small if the initial state is related to the Bunch-Davies state by a Bogoliubov transformation and the energy density in the state is small enough so that the usual slow-roll conditions are obeyed. Bogoliubov states that lead to violations of the slow-roll conditions, as well as more general excited states, require more careful treatment and will be discussed in a separate publication.
Clouds and the Faint Young Sun Paradox

Abstract. We investigate the role which clouds could play in resolving the Faint Young Sun Paradox (FYSP). Lower solar luminosity in the past means that less energy was absorbed on Earth (a forcing of −50 W m−2 during the late Archean), but geological evidence points to the Earth having been at least as warm as it is today, with only very occasional glaciations. We perform radiative calculations on a single global mean atmospheric column. We select a nominal set of three layered, randomly overlapping clouds, which are both consistent with observed cloud climatologies and reproduced the observed global mean energy budget of Earth. By varying the fraction, thickness, height and particle size of these clouds we conduct a wide exploration of how changed clouds could affect climate, thus constraining how clouds could contribute to resolving the FYSP. Low clouds reflect sunlight but have little greenhouse effect. Removing them entirely gives a forcing of +25 W m−2 whilst more modest reduction in their efficacy gives a forcing of +10 to +15 W m−2. For high clouds, the greenhouse effect dominates. It is possible to generate +50 W m−2 forcing from enhancing these, but this requires making them 3.5 times thicker and 14 K colder than the standard high cloud in our nominal set and expanding their coverage to 100% of the sky. Such changes are not credible. More plausible changes would generate no more than +15 W m−2 forcing. Thus neither fewer low clouds nor more high clouds can provide enough forcing to resolve the FYSP. Decreased surface albedo can contribute no more than +5 W m−2 forcing. Some models which have been applied to the FYSP do not include clouds at all. These overestimate the forcing due to increased CO2 by 20 to 25% when pCO2 is 0.01 to 0.1 bar.
A functor-valued invariant of tangles

We construct a family of rings. To a plane diagram of a tangle we associate a complex of bimodules over these rings. Chain homotopy equivalence class of this complex is an invariant of the tangle. On the level of Grothendieck groups this invariant descends to the Kauffman bracket of the tangle. When the tangle is a link, the invariant specializes to the bigraded cohomology theory introduced in our earlier work.
Evolution of Planetary Orbits with Stellar Mass Loss and Tidal Dissipation

Intermediate mass stars and stellar remnants often host planets, and these dynamical systems evolve because of mass loss and tides. This paper considers the combined action of stellar mass loss and tidal dissipation on planetary orbits in order to determine the conditions required for planetary survival. Stellar mass loss is included using a so-called Jeans model, described by a dimensionless mass loss rate γ and an index β. We use an analogous prescription to model tidal effects, described here by a dimensionless dissipation rate Γ and two indices (q, p). The initial conditions are determined by the starting value of angular momentum parameter η0 (equivalently, the initial eccentricity) and the phase θ of the orbit. Within the context of this model, we derive an analytic formula for the critical dissipation rate Γ, which marks the boundary between orbits that spiral outward due to stellar mass loss and those that spiral inward due to tidal dissipation. This analytic result Γ = Γ(γ, β, q, p, η0, θ) is essentially exact for initially circular orbits and holds to within an accuracy of ≈50% over the entire multi-dimensional parameter space, where the individual parameters vary by several orders of magnitude. For stars that experience mass loss, the stellar radius often displays quasi-periodic variations, which produce corresponding variations in tidal forcing; we generalize the calculation to include such pulsations using a semi-analytic treatment that holds to the same accuracy as the non-pulsating case. These results can be used in many applications, e.g., to predict/constrain properties of planetary systems orbiting white dwarfs.
Optical spectroscopy of molecular junctions: Nonequilibrium Green’s functions perspective

We consider optical spectroscopy of molecular junctions from the quantum transport perspective when radiation field is quantized and optical response of the system is simulated as photon flux. Using exact expressions for photon and electronic fluxes derived within the nonequilibrium Green function (NEGF) methodology and utilizing fourth order diagrammatic perturbation theory (PT) in molecular coupling to radiation field, we perform simulations employing realistic parameters. Results of the simulations are compared to the bare PT which is usually employed in studies on nonlinear optical spectroscopy to classify optical processes. We show that the bare PT violates conservation laws, while flux conserving NEGF formulation mixes optical processes.
RELATIVISTIC ELECTRONS ON A ROTATING SPHERICAL MAGNETIC DIPOLE: SURFACE ORBITALS

The semiclassical orbitals of a relativistic electron on a rotating sphere threaded by an intense magnetic dipole field are examined. Several physically distinct regimes emerge, depending on the relative sizes of the mass, total energy, canonical azimuthal angular momentum, and magnetic field strength. Magnetic flux enclosed by orbits is quantized very close to the poles, suggesting a quantum Hall-like state. Application of this system to neutron star surfaces is outlined.
The Hot Components of AM CVn Helium Cataclysmics

We present the results of a multi-component synthetic spectral analysis of the archival far-ultraviolet spectra of the hot components of several AM CVn double degenerate interacting binaries with known distances from trigonometric parallaxes. Our analysis was carried out using the code BINSYN, which takes into account the donor companion star, the shock front which forms at the disk edge, and the FUV and NUV energy distribution. We fixed the distance of each system at its parallax-derived value and adopted appropriate values of orbital inclination and white dwarf (WD) mass. We find that the accretion-heated 'DO/DB' WDs are contributing significantly to the FUV flux in five of the systems (ES Ceti, CR Boo, V803 Cen, HP Lib, GP Com). In three of the systems, GP Com, ES Ceti, and CR Boo, the WD dominates the FUV/NUV flux. We present model-derived accretion rates which agree with the low end of the range of accretion rates derived earlier from blackbody fits over the entire spectral energy distribution. We find that the WD in ES Ceti is very likely not a direct impact accretor but has a small disk. The WD in ES Ceti has T{sub eff} {approx} 40, 000 {+-} 10, 000 K.more » This is far cooler than the previous estimate of Espaillat et al.. We find that the WD in GP Com has T{sub eff} = 14, 800 {+-} 500 K, which is hotter than the previously estimated temperature of 11,000 K. We present a comparison between our empirical results and current theoretical predictions for these systems.« less
Quantifying Intimacy in Language

Intimacy is a fundamental aspect of how we relate to others in social settings. Language encodes the social information of intimacy through both topics and other more subtle cues (such as linguistic hedging and swearing). Here, we introduce a new computational framework for studying expressions of the intimacy in language with an accompanying dataset and deep learning model for accurately predicting the intimacy level of questions (Pearson r = 0.87). Through analyzing a dataset of 80.5M questions across social media, books, and films, we show that individuals employ interpersonal pragmatic moves in their language to align their intimacy with social settings. Then, in three studies, we further demonstrate how individuals modulate their intimacy to match social norms around gender, social distance, and audience, each validating key findings from studies in social psychology. Our work demonstrates that intimacy is a pervasive and impactful social dimension of language.
Learning Lyapunov (Potential) Functions from Counterexamples and Demonstrations

We present a technique for learning control Lyapunov (potential) functions, which are used in turn to synthesize controllers for nonlinear dynamical systems. The learning framework uses a demonstrator that implements a black-box, untrusted strategy presumed to solve the problem of interest, a learner that poses finitely many queries to the demonstrator to infer a candidate function and a verifier that checks whether the current candidate is a valid control Lyapunov function. The overall learning framework is iterative, eliminating a set of candidates on each iteration using the counterexamples discovered by the verifier and the demonstrations over these counterexamples. We prove its convergence using ellipsoidal approximation techniques from convex optimization. We also implement this scheme using nonlinear MPC controllers to serve as demonstrators for a set of state and trajectory stabilization problems for nonlinear dynamical systems. Our approach is able to synthesize relatively simple polynomial control Lyapunov functions, and in that process replace the MPC using a guaranteed and computationally less expensive controller.
Divisibility of binomial coefficients and generation of alternating groups

We examine an elementary problem on prime divisibility of binomial coefficients. Our problem is motivated by several related questions on alternating groups.
Bayeswave: Bayesian inference for gravitational wave bursts and instrument glitches

A central challenge in gravitational wave astronomy is identifying weak signals in the presence of non-stationary and non-Gaussian noise. The separation of gravitational wave signals from noise requires good models for both. When accurate signal models are available, such as for binary Neutron star systems, it is possible to make robust detection statements even when the noise is poorly understood. In contrast, searches for 'un-modeled' transient signals are strongly impacted by the methods used to characterize the noise. Here we take a Bayesian approach and introduce a multi-component, variable dimension, parameterized noise model that explicitly accounts for non-stationarity and non-Gaussianity in data from interferometric gravitational wave detectors. Instrumental transients (glitches) and burst sources of gravitational waves are modeled using a Morlet–Gabor continuous wavelet frame. The number and placement of the wavelets is determined by a trans-dimensional reversible jump Markov chain Monte Carlo algorithm. The Gaussian component of the noise and sharp line features in the noise spectrum are modeled using the BayesLine algorithm, which operates in concert with the wavelet model.