cssi/SciSciGPT-SciSciNet huggingface dataset:
Propagating and evanescent internal waves in a deep ocean model

We present experimental and computational studies of the propagation of internal waves in a stratified fluid with an exponential density profile that models the deep ocean. The buoyancy frequency profile N.z/ (proportional to the square root of the density gradient) varies smoothly by more than an order of magnitude over the fluid depth, as is common in the deep ocean. The non-uniform stratification is characterized by a turning depth zc, where N.zc/ is equal to the wave frequency ! and N.z< zc/ < !. Internal waves reflect from the turning depth and become evanescent below the turning depth. The energy flux below the turning depth is shown to decay exponentially with a decay constant given by kc, which is the horizontal wavenumber at the turning depth. The viscous decay of the vertical velocity amplitude of the incoming and reflected waves above the turning depth agree within a few per cent with a previously untested theory for a fluid of arbitrary stratification (Kistovich and Chashechkin, J. Appl. Mech. Tech. Phys., vol. 39, 1998, pp. 729‐737).
Vanishing of Symplectic Homology and Obstruction to Flexible Fillability

For any asymptotically dynamically convex contact manifold $Y$, we show that $SH_*(W)=0$ is a property independent of the choice of topologically simple (i.e.\ $c_1(W)=0$ and $\pi_{1}(Y)\rightarrow \pi_1(W)$ is injective) Liouville filling $W$. In particular, if $Y$ is the boundary of a flexible Weinstein domain, then any topologically simple Liouville filling $W$ has vanishing symplectic homology. As a consequence, we answer a question of Lazarev partially: a contact manifold $Y$ admitting flexible fillings determines the integral cohomology of all the topologically simple Liouville fillings of $Y$. The vanishing result provides an obstruction to flexible fillability. As an application, we show that all Brieskorn manifolds of dimension $\ge 5$ cannot be filled by flexible Weinstein manifolds.
A Penrose-like inequality with charge

We establish a Penrose-like inequality for general (not necessarily time-symmetric) initial data sets of the Einstein–Maxwell equations, which satisfy the dominant energy condition. More precisely, it is shown that the ADM energy is bounded below by an expression which is proportional to the sum of the square root of the area of the outermost future (or past) apparent horizon and the square of the total charge. The proportionality constants depend on the solution to a linear elliptic equation which incorporates the charge. In addition, a corrected version of the Penrose-like inequality (Commun Math Phys 290(2):779–788, 2009) is presented.
POINTER: Constrained Progressive Text Generation via Insertion-based Generative Pre-training

Large-scale pre-trained language models, such as BERT and GPT-2, have achieved excellent performance in language representation learning and free-form text generation. However, these models cannot be directly employed to generate text under specified lexical constraints. To address this challenge, we present POINTER (PrOgressive INsertion-based TransformER), a simple yet novel insertion-based approach for hard-constrained text generation. The proposed method operates by progressively inserting new tokens between existing tokens in a parallel manner. This procedure is recursively applied until a sequence is completed. The resulting coarse-to-fine hierarchy makes the generation process intuitive and interpretable. We pre-train our model with the proposed progressive insertion-based objective on a 12GB Wikipedia dataset, and fine-tune it on downstream hard-constrained generation tasks. Non-autoregressive decoding yields a logarithmic time complexity during inference time. Experimental results on both News and Yelp datasets demonstrate that Pointer achieves state-of-the-art performance on constrained text generation. We released the pre-trained models and the source code to facilitate future research.
STERILE NEUTRINOS AND PULSAR VELOCITIES REVISITED

We calculate the momentum given to a proto-neutron star during the first 10 s after temperature equilibrium is reached, using recent evidence of sterile neutrinos and a measurement of the mixing angle. This is a continuation of an earlier estimate with a wide range of possible mixing angles. Using the new mixing angle we find that sterile neutrinos can account for the observed pulsar velocities.
Bayesian Methods for Joint Exoplanet Transit Detection and Systematic Noise Characterization

The treatment of systematic noise is a significant aspect of transit exoplanet data processing due to the signal strength of systematic noise relative to a transit signal. Typically the standard approach to transit detection is to estimate and remove systematic noise independently of and prior to a transit detection test. If a transit signal is present in a light curve, the process of systematic noise removal may distort the transit signal by overfitting and thereby reduce detection efficiency. We present a Bayesian framework for joint detection of transit signals and systematic noise characterization and describe the implementation of these detectors as optimal Neyman-Pearson likelihood ratio tests. The joint detectors reduce to closed form as matched filters under the assumption of a Gaussian Bayesian prior for the systematic noise. The performance of the exploratory detectors was evaluated in injection tests and show $\sim 2\%$ improvement in overall detection efficiency relative to the standard approach. We find that joint detection efficiency is specifically improved for short-period, low transit-depth exoplanet transits, providing evidence in support of the hypothesis that joint detection may indeed help to mitigate overfitting. In addition, an initial feasibility test to detect known exoplanets in Kepler data using the joint detectors produced encouraging preliminary results.
Quantum Phase Transition in the Yukawa-SYK Model

The authors analyze the quantum phases in a Yukawa-SYK model. They show that the model has a maximally chaotic non-Fermi liquid phase and an incompressible insulating phase.
The radion as a dark matter candidate

I study a class of Randall–Sundrum (RS) models with Spontaneous Breaking of Scale Invariance (SBSI). This class of models implements the Contino–Pomarol–Rattazzi (CPR) mechanism to achieve SBSI thr...
Hausdorff dimension of level sets of generalized Takagi functions

This paper examines level sets of two families of continuous, nowhere differentiable functions (one a subfamily of the other) defined in terms of the "tent map". The well-known Takagi function is a special case. Sharp upper bounds are given for the Hausdorff dimension of the level sets of functions in these two families. Furthermore, the case where a function f is chosen at random from either family is considered, and results are given for the Hausdorff dimension of the zero set and the set of maximum points of f.
Skew flat fibrations

A fibration of \(\mathbb R^n\) by oriented copies of \(\mathbb R^p\) is called skew if no two fibers intersect nor contain parallel directions. Conditions on p and n for the existence of such a fibration were given by Ovsienko and Tabachnikov. A classification of smooth fibrations of \(\mathbb R^3\) by skew oriented lines was given by Salvai, in analogue with the classification of oriented great circle fibrations of \(S^3\) by Gluck and Warner. We show that Salvai’s classification has a topological variation which generalizes to characterize all continuous fibrations of \(\mathbb R^n\) by skew oriented copies of \(\mathbb R^p\). We show that the space of fibrations of \(\mathbb R^3\) by skew oriented lines deformation retracts to the subspace of Hopf fibration, and therefore has the homotopy type of a pair of disjoint copies of \(S^2\). We discuss skew fibrations in the complex and quaternionic setting and give a necessary condition for the existence of a fibration of \(\mathbb C^n\) (respectively, \(\mathbb H^n\)) by skew oriented copies of \(\mathbb C^p\) (respectively, \(\mathbb H^p\)).
Persistent energy-time entanglement covering multiple resonances of an on-chip biphoton frequency comb

We investigate the time-frequency signatures of an on-chip biphoton frequency comb (BFC) generated from a silicon nitride microring resonator. Using a Franson interferometer, we examine the multifrequency nature of the photon pair source in a time entanglement measurement scheme; having multiple frequency modes from the BFC results in a modulation of the interference pattern. This measurement together with a Schmidt mode decomposition shows that the generated continuous variable energy–time entangled state spans multiple pair-wise modes. Additionally, we demonstrate nonlocal dispersion cancellation, a foundational concept in time–energy entanglement, suggesting the potential of the chip-scale BFC for large-alphabet quantum key distribution.
Just a Taste: Lectures on Flavor Physics

We review the flavor structure of the Standard Model and the ways in which the flavor parameters are measured. This is an extended writeup of the TASI 2016 lectures on flavor physics. Earlier versions of these notes were presented at pre-SUSY 2015 and Cornell University’s Physics 7661 course in 2010.
Reconnection in Marginally Collisionless Accretion Disk Coronae

We point out that a conventional construction placed on observations of accreting black holes, in which their nonthermal X-ray spectra are produced by inverse Comptonization in a coronal plasma, suggests that the plasma is marginally collisionless. Recent developments in plasma physics indicate that fast reconnection takes place only in collisionless plasmas. As has recently been suggested for the Sun's corona, such marginal states may result from a combination of energy balance and the requirements of fast magnetic reconnection.
Structural Supervision Improves Few-Shot Learning and Syntactic Generalization in Neural Language Models

Humans can learn structural properties about a word from minimal experience, and deploy their learned syntactic representations uniformly in different grammatical contexts. We assess the ability of modern neural language models to reproduce this behavior in English and evaluate the effect of structural supervision on learning outcomes. First, we assess few-shot learning capabilities by developing controlled experiments that probe models' syntactic nominal number and verbal argument structure generalizations for tokens seen as few as two times during training. Second, we assess invariance properties of learned representation: the ability of a model to transfer syntactic generalizations from a base context (e.g., a simple declarative active-voice sentence) to a transformed context (e.g., an interrogative sentence). We test four models trained on the same dataset: an n-gram baseline, an LSTM, and two LSTM-variants trained with explicit structural supervision. We find that in most cases, the neural models are able to induce the proper syntactic generalizations after minimal exposure, often from just two examples during training, and that the two structurally supervised models generalize more accurately than the LSTM model. All neural models are able to leverage information learned in base contexts to drive expectations in transformed contexts, indicating that they have learned some invariance properties of syntax.
Photon Statistics Limits for Earth-Based Parallax Measurements of MACHO Events

We analyze the limitations imposed by photon-counting statistics on extracting useful information about MACHOs from Earth-based parallax observations of microlensing events. We find that if one or more large (say 2.5 m) telescopes are dedicated to observing a MACHO event for several nights near maximum amplification, then it is possible, in principle, to measure the velocity of the MACHO well enough to distinguish between disk and halo populations for events with ωAm2 1 day−1, where ω−1 denotes the timescale of the event and Am denotes its maximum amplification. Thus, if it turns out to be possible to reduce all other sources of error to below that of photon statistics, it may be feasible to do useful Earth-based parallax observations for high amplification events.
Effective localization number: Building k-surviving degrees

We introduce and study effective versions of the localization numbers introduced by Newelski and Roslanowski (cite in paper). We show that proper hierarchies are produced, and that the corresponding highness notions are relatively weak, in that they can often be made computably traceable. We discuss connections with other better-understood effective cardinal characteristics.
Forecasting Solar Cycle 25 Using Deep Neural Networks

With recent advances in the field of machine learning, the use of deep neural networks for time series forecasting has become more prevalent. The quasi-periodic nature of the solar cycle makes it a good candidate for applying time series forecasting methods. We employ a combination of WaveNet and Long Short-Term Memory neural networks to forecast the sunspot number using the years 1749 to 2019 and total sunspot area using the years 1874 to 2019 time series data for the upcoming Solar Cycle 25. Three other models involving the use of LSTMs and 1D ConvNets are also compared with our best model. Our analysis shows that the WaveNet and LSTM model is able to better capture the overall trend and learn the inherent long and short term dependencies in time series data. Using this method we forecast 11 years of monthly averaged data for Solar Cycle 25. Our forecasts show that the upcoming Solar Cycle 25 will have a maximum sunspot number around 106 ± 19.75 and maximum total sunspot area around 1771 ± 381.17. This indicates that the cycle would be slightly weaker than Solar Cycle 24.
Analytic Coleman-De Luccia geometries

We present the necessary and sufficient conditions for a Euclidean scale factor to be a solution of the Coleman-de Luccia equations for some analytic potential V ({psi}), with a Lorentzian continuation describing the growth of a bubble of lower-energy vacuum surrounded by higher-energy vacuum. We then give a set of explicit examples that satisfy the conditions and thus are closed-form analytic examples of Coleman-de Luccia geometries.
Diffusive Stability of Turing Patterns via Normal Forms

We investigate dynamics near Turing patterns in reaction–diffusion systems posed on the real line. Linear analysis predicts diffusive decay of small perturbations. We construct a “normal form” coordinate system near such Turing patterns which exhibits an approximate discrete conservation law. The key ingredients to the normal form is a conjugation of the reaction–diffusion system on the real line to a lattice dynamical system. At each lattice site, we decompose perturbations into neutral phase shifts and normal decaying components. As an application of our normal form construction, we prove nonlinear stability of Turing patterns with respect to perturbations that are small in $$L^1\cap L^\infty $$ , with sharp rates, recovering and slightly improving on results in Johnson and Zumbrun (Ann Inst H Poincare Anal Non Lineaire 28:471–483, 2011) and Schneider (Commun Math Phys 178:679–702, 1996).
nSQUID arrays as conveyers of quantum information

We have considered the quantum dynamics of an array of nSQUIDs—two-junction SQUIDs with negative mutual inductance between their two arms. Effective dual-rail structure of the array creates additional internal degree of freedom for the fluxons in the array, which can be used to encode and transport quantum information. Physically, this degree of freedom is represented by electromagnetic excitations localized on the fluxon. We have calculated the spatial profile and frequency spectrum of these excitations. Their dynamics can be reduced to two quantum states, so that each fluxon moving through the array carries with it a qubit of information. Coherence properties of such a propagating qubit in the nSQUID array are characterized by the dynamic suppression of the low-frequency decoherence due to the motion-induced spreading of the noise spectral density to a larger frequency interval.
Connected sums and involutive knot Floer homology

We prove a formula for the conjugation action on the knot Floer complex of the connected sum of two knots. Using the formula we construct a homomorphism from the smooth concordance group to an abelian group consisting of chain complexes with homotopy automorphisms, modulo an equivalence relation. Using our connected sum formula, we perform some example computations of Hendricks and Manolescu's involutive invariants on large surgeries of connected sums of knots.
Secure State Estimation Against Sensor Attacks in the Presence of Noise

We consider the problem of estimating the state of a noisy linear dynamical system when an unknown subset of sensors is arbitrarily corrupted by an adversary. We propose a secure state estimation algorithm, and derive (optimal) bounds on the achievable state estimation error given an upper bound on the number of attacked sensors. The proposed state estimator involves Kalman filters operating over subsets of sensors to search for a sensor subset which is reliable for state estimation. To further improve the subset search time, we propose Satisfiability Modulo Theory-based techniques to exploit the combinatorial nature of searching over sensor subsets. Finally, as a result of independent interest, we give a coding theoretic view of attack detection and state estimation against sensor attacks in a noiseless dynamical system.
Rigorous Results for Hierarchical Models of Structural Glasses

We consider two non-mean-field models of structural glasses built on a hierarchical lattice. First, we consider a hierarchical version of the random energy model, and we prove the existence of the thermodynamic limit and self-averaging of the free energy. Furthermore, we prove that the infinite-volume entropy is positive in a high-temperature region bounded from below, thus providing an upper bound on the Kauzmann critical temperature. In addition, we show how to improve this bound by leveraging the hierarchical structure of the model. Finally, we introduce a hierarchical version of the $$p$$ -spin model of a structural glass, and we prove the existence of the thermodynamic limit and self-averaging of the free energy.
Room-temperature high on/off ratio in suspended graphene nanoribbon field-effect transistors.

We have fabricated suspended few-layer (1–3 layers) graphene nanoribbon field-effect transistors from unzipped multi-wall carbon nanotubes. Electrical transport measurements show that current annealing effectively removes the impurities on the suspended graphene nanoribbons, uncovering the intrinsic ambipolar transfer characteristic of graphene. Further increasing the annealing current creates a narrow constriction in the ribbon, leading to the formation of a large bandgap and subsequent high on/off ratio (which can exceed 104). Such fabricated devices are thermally and mechanically stable: repeated thermal cycling has little effect on their electrical properties. This work shows for the first time that ambipolar field-effect characteristics and high on/off ratios at room temperature can be achieved in relatively wide graphene nanoribbons (15–50 nm) by controlled current annealing.
The Dust Temperature of the “Dusty” Radio Galaxy MG 1019+0535: Evidence for an Outflow

Radio galaxies characteristically have strong Lyα emission lines. However, a few have Lyα equivalent widths that are substantially weaker in relation to other emission lines. One in particular, MG 1019+0535 (z = 2.765), was studied by Dey, Spinrad, & Dickinson in 1995. We report on our reduction of Infrared Space Observatory (ISO) data in the 160 μm band for this galaxy. We also compile information on two other high-redshift active galaxies with weak Lyα lines, the radio galaxy TXS 0211-122 and the AGN-starburst galaxy F10214+4724, to provide a small weak-Lyα line sample. IRAS plus ISO data show that F10214+4724 has a temperature 89 ± 12 K. TXS 0211-122 was not detected in either the submillimeter or microwave. Submillimeter measurements of MG 1019+0535 by Cimatti et al. were suggestive of a dust temperature in the range 35 K ≤ Td ≤ 80 K. However, our 2 σ upper limit on the flux at 160 μm shows that Td 32 K. An energy argument based on observations which constrain the total optical extinction strongly suggests that the dust temperature must be even lower: Td20 K. We find the contrast between the high-temperature dust in the active starburst galaxy and the low-temperature dust in the evolved, albeit active galaxy, is consistent with an expanding cloud of dust. We find that the temperature range can be reconciled if we are seeing MG 1019+0535 at a poststarburst age of ≈500–700 Myr, with the bulk of its dust cloud at a galactocentric distance Rd 300 kpc.
Duality group actions on fermions

In this short paper we look at the action of T-duality and string duality groups on fermions, in maximally-supersymmetric theories and related theories. Briefly, we argue that typical duality groups such as SL(2, ℤ) have sign ambiguities in their actions on fermions, and propose that pertinent duality groups be extended by ℤ2, to groups such as the metaplectic group. Specifically, we look at duality groups arising from mapping class groups of tori in M theory compactifications, T-duality, ten-dimensional type IIB S-duality, and (briefly) four-dimensional N = 4 super Yang-Mills, and in each case, propose that the full duality group is a nontrivial ℤ2 extension of the duality group acting on bosonic degrees of freedom, to more accurately describe possible actions on fermions. We also walk through U-duality groups for toroidal compactifications to nine, eight, and seven dimensions, which enables us to perform cross-consistency tests of these proposals.
Life's Chirality From Prebiotic Environments

A key open question in the study of life is the origin of biomolecular homochirality: almost every life-form on Earth has exclusively levorotary amino acids and dextrorotary sugars. Will the same handedness be preferred if life is found elsewhere? We review some of the pertinent literature and discuss recent results suggesting that life’s homochirality resulted from sequential chiral symmetry breaking triggered by environmental events. In one scenario, autocatalytic prebiotic reactions undergo stochastic uctuations due to environmental disturbances. In another, chiral-selective polymerization reaction rates inuenced by environmental eects lead to substantial chiral excess even in the absence of autocatalysis. Applying these arguments to other potentially life-bearing platforms has implications to the search for extraterrestrial life: we predict that a statistically representative sampling of extraterrestrial stereochemistry will be racemic (chirally neutral) on average.
On the Capillarity Equation in Two Dimensions

We study the capillarity equation from the global point of view of behavior of its solutions without explicit regard to boundary conditions. We show its solutions to be constrained in ways, that have till now not been characterized in literature known to us.
Bondi on spherically symmetric accretion

Hermann Bondi's 1952 paper "On spherically symmetrical accretion" is recognized as one of the foundations of accretion theory. Although Bondi later remarked that it was "not much more than an examination exercise", his mathematical analysis of spherical accretion on to a point mass has found broad use across fields of astrophysics that were embryonic or non-existent at the time of the paper's publication. In this non-technical review, I describe the motivations for Bondi's work, and briefly discuss some of the applications of Bondi accretion in high energy astrophysics, galaxy formation, and star formation.
Compiling quantum circuits to realistic hardware architectures using temporal planners

To run quantum algorithms on emerging gate-model quantum hardware, quantum circuits must be compiled to take into account constraints on the hardware. For near-term hardware, with only limited means to mitigate decoherence, it is critical to minimize the duration of the circuit. We investigate the application of temporal planners to the problem of compiling quantum circuits to newly emerging quantum hardware. While our approach is general, we focus on compiling to superconducting hardware architectures with nearest neighbor constraints. Our initial experiments focus on compiling Quantum Alternating Operator Ansatz (QAOA) circuits whose high number of commuting gates allow great flexibility in the order in which the gates can be applied. That freedom makes it more challenging to find optimal compilations but also means there is a greater potential win from more optimized compilation than for less flexible circuits. We map this quantum circuit compilation problem to a temporal planning problem, and generated a test suite of compilation problems for QAOA circuits of various sizes to a realistic hardware architecture. We report compilation results from several state-of-the-art temporal planners on this test set. This early empirical evaluation demonstrates that temporal planning is a viable approach to quantum circuit compilation.
Game-Theoretic Analysis of the Hegselmann-Krause Model for Opinion Dynamics in Finite Dimensions

We consider the Hegselmann-Krause model for opinion dynamics and study the evolution of the system under various settings. We first analyze the termination time of the synchronous Hegselmann-Krause dynamics in arbitrary finite dimensions and show that the termination time in general only depends on the number of agents involved in the dynamics. To the best of our knowledge, that is the sharpest bound for the termination time of such dynamics that removes dependency of the termination time from the dimension of the ambient space, and connects the convergence speed of the dynamics to the eigenvalues of the adjacency matrix of the connectivity graph in the Hegselmann-Krause dynamics. This answers an open question in the paper by Bhattacharyya et al. on how to obtain a tighter upper bound for the termination time. Furthermore, we study the asynchronous Hegselmann-Krause model from a novel game-theoretic approach and show that the evolution of an asynchronous Hegselmann-Krause model is equivalent to a sequence of best response updates in a well-designed potential game. We then provide a polynomial upper bound for the expected time and expected number of switching topologies until the dynamic reaches an arbitrarily small neighborhood of its equilibrium points, provided that the agents update uniformly at random. This is a step toward analysis of heterogeneous Hegselmann-Krause dynamics. Finally, we consider the heterogeneous Hegselmann-Krause dynamics and provide a necessary condition for the finite termination time of such dynamics. In particular, we sketch some future directions toward more detailed analysis of the heterogeneous Hegselmann-Krause model.
Radiating Current Sheets in the Solar Chromosphere

An MHD model of a hydrogen plasma with flow, an energy equation, NLTE ionization and radiative cooling, and an Ohm's law with anisotropic electrical conduction and thermoelectric effects is used to self-consistently generate atmospheric layers over a 50 km height range. A subset of these solutions contains current sheets and has properties similar to those of the lower and middle chromosphere. The magnetic field profiles are found to be close to Harris sheet profiles, with maximum field strengths {approx}25-150 G. The radiative flux F{sub R} emitted by individual sheets is {approx}4.9 Multiplication-Sign 10{sup 5}-4.5 Multiplication-Sign 10{sup 6} erg cm{sup -2} s{sup -1}, to be compared with the observed chromospheric emission rate of {approx}10{sup 7} erg cm{sup -2} s{sup -1}. Essentially all emission is from regions with thicknesses {approx}0.5-13 km containing the neutral sheet. About half of F{sub R} comes from sub-regions with thicknesses 10 times smaller. A resolution {approx}< 5-130 m is needed to resolve the properties of the sheets. The sheets have total H densities {approx}10{sup 13}-10{sup 15} cm{sup -3}. The ionization fraction in the sheets is {approx}2-20 times larger, and the temperature is {approx}2000-3000 K higher than in the surrounding plasma. The Joule heating flux F{sub J} exceedsmore » F{sub R} by {approx}4%-34%, the difference being balanced in the energy equation mainly by a negative compressive heating flux. Proton Pedersen current dissipation generates {approx}62%-77% of the positive contribution to F{sub J} . The remainder of this contribution is due to electron current dissipation near the neutral sheet where the plasma is weakly magnetized.« less
Time-Dependent Two-Fluid Magnetohydrodynamic Model and Simulation of the Chromosphere

The Sun’s chromosphere is a highly dynamic, partially ionized region where spicules (hot jets of plasma) form. Here we present a two-fluid MHD model to study the chromosphere, which includes ion–neutral interaction and frictional heating. Our simulation recovers a magnetic-canopy shape that forms quickly, but it is also quickly disrupted by the formation of a jet. Our simulation produces a shock self-consistently, where the jet is driven by the frictional heating, which is much greater than the ohmic heating. Thus, our simulation demonstrates that the jet could be driven purely by thermal effects due to ion–neutral collisions and not by magnetic reconnection. We plan to improve the model to include photo-chemical effects and radiation.
Dynamic Coupling of Convective Flows and Magnetic Field during Flux Emergence

We simulate the buoyant rise of a magnetic flux rope from the solar convection zone into the corona to better understand the energetic coupling of the solar interior to the corona. The magnetohydrodynamic model addresses the physics of radiative cooling, coronal heating, and ionization, which allow us to produce a more realistic model of the solar atmosphere. The simulation illustrates the process by which magnetic flux emerges at the photosphere and coalesces to form two large concentrations of opposite polarities. We find that the large-scale convective motion in the convection zone is critical to form and maintain sunspots, while the horizontal converging flows in the near-surface layer prevent the concentrated polarities from separating. The footpoints of the sunspots in the convection zone exhibit a coherent rotation motion, resulting in the increasing helicity of the coronal field. Here, the local configuration of the convection causes the convergence of opposite polarities of magnetic flux with a shearing flow along the polarity inversion line. During the rising of the flux rope, the magnetic energy is first injected through the photosphere by the emergence, followed by energy transport by horizontal flows, after which the energy is subducted back to the convection zone by the submerging flows.
A comparison of frequency downshift models of wave trains on deep water

Frequency downshift (FD) in wave trains on deep water occurs when a measure of the frequency, typically the spectral peak or the spectral mean, decreases as the waves evolve. Many FD models rely on wind or wave breaking. We consider seven models that do not include these effects and compare their predictions with four sets of experiments that also do not include these effects. The models are the (i) nonlinear Schrodinger equation (NLS), (ii) dissipative NLS equation (dNLS), (iii) Dysthe equation, (iv) viscous Dysthe equation (vDysthe), (v) Gordon equation (Gordon), which has a free parameter, (vi) Islas-Schober equation (IS), which has a free parameter, and (vii) a new model, the dissipative Gramstad-Trulsen (dGT) equation. The dGT equation has no free parameters and addresses some of the difficulties associated with the vDysthe equation. We compare a measure of overall error and the evolution of the spectral amplitudes, means, and peaks. We find the following: (i) The NLS and Dysthe equations do not accurately predict the spectral amplitudes. (ii) The Gordon equation, which is a successful model of FD in optics, does not accurately model FD in water waves, regardless of the choice of free parameter. (iii) The dNLS, vDysthe, dGT, and IS (with optimized free parameter) models do a reasonable job predicting the measured spectral amplitudes, but none captures all spectral evolutions. (iv) The vDysthe, dGT, and IS models most accurately predict the observed evolution of the spectral peak and the spectral mean. (v) The IS and vDysthe models have the smallest overall errors.Frequency downshift (FD) in wave trains on deep water occurs when a measure of the frequency, typically the spectral peak or the spectral mean, decreases as the waves evolve. Many FD models rely on wind or wave breaking. We consider seven models that do not include these effects and compare their predictions with four sets of experiments that also do not include these effects. The models are the (i) nonlinear Schrodinger equation (NLS), (ii) dissipative NLS equation (dNLS), (iii) Dysthe equation, (iv) viscous Dysthe equation (vDysthe), (v) Gordon equation (Gordon), which has a free parameter, (vi) Islas-Schober equation (IS), which has a free parameter, and (vii) a new model, the dissipative Gramstad-Trulsen (dGT) equation. The dGT equation has no free parameters and addresses some of the difficulties associated with the vDysthe equation. We compare a measure of overall error and the evolution of the spectral amplitudes, means, and peaks. We find the following: (i) The NLS and Dysthe equations do not accu...
Premelting, fluctuations, and coarse-graining of water-ice interfaces

Using statistical field theory supplemented with molecular dynamics simulations, we consider premelting on the surface of ice as a generic consequence of broken hydrogen bonds at the boundary between the condensed and gaseous phases. A procedure for coarse-graining molecular configurations onto a continuous scalar order parameter field is discussed, which provides a convenient representation of the interface between locally crystal-like and locally liquid-like regions. A number of interfacial properties are straightforwardly evaluated using this procedure such as the average premelting thickness and surface tension. The temperature and system size dependence of the premelting layer thickness calculated in this way confirms the characteristic logarithmic growth expected for the scalar field theory that the system is mapped onto through coarse-graining, though remains finite due to long-ranged interactions. Finally, from explicit simulations the existence of a premelting layer is shown to be insensitive to bulk lattice geometry, exposed crystal face, and curvature.
Coulomb interaction and the Fermi liquid state: solution by bosonization

We investigate the effects of the Coulomb two-body interaction on Fermi liquids via bosonization in two and three spatial dimensions. The Coulomb interaction is singular in the limit of low momentum transfer, and recent interest in the possibility that some singular interactions might destroy the Fermi liquid state motivate us to reexamine it. We calculate the exact boson correlation function to show that the Fermi liquid state is retained in the case of Coulomb interactions in two and three dimensions. Spin and charge degrees of freedom propagate together at the same velocity and collective charge excitations (plasmons) exhibit the expected energy gap in three dimensions. Non-Fermi liquid behaviour occurs in two dimensions, however, for a super-long-range interaction studied recently by Bares and Wen.
Do Periodicities in Extinction—with Possible Astronomical Connections—Survive a Revision of the Geological Timescale?

A major revision of the geological timescale was published in 2012. We re-examine our past finding of a 27 Myr periodicity in marine extinction rates by re-assigning dates to the extinction data used previously. We find that the spectral power in this period is somewhat increased, and persists at a narrow bandwidth, which supports our previous contention that the Nemesis hypothesis is untenable as an explanation for the periodicity that was first noted by Raup & Sepkoski in the 1980s. We enumerate a number of problems in a recent study comparing extinction rates with time series models.
Evolving modular genetic regulatory networks with a recursive, top-down approach

Being able to design genetic regulatory networks (GRNs) to achieve a desired cellular function is one of the main goals of synthetic biology. However, determining minimal GRNs that produce desired time-series behaviors is non-trivial. In this paper, we propose a 'top-down' approach to evolving small GRNs and then use these to recursively boot-strap the identification of larger, more complex, modular GRNs. We start with relatively dense GRNs and then use differential evolution (DE) to evolve interaction coefficients. When the target dynamical behavior is found embedded in a dense GRN, we narrow the focus of the search and begin aggressively pruning out excess interactions at the end of each generation. We first show that the method can quickly rediscover known small GRNs for a toggle switch and an oscillatory circuit. Next we include these GRNs as non-evolvable subnetworks in the subsequent evolution of more complex, modular GRNs. Successful solutions found in canonical DE where we truncated small interactions to zero, with or without an interaction penalty term, invariably contained many excess interactions. In contrast, by incorporating aggressive pruning and the penalty term, the DE was able to find minimal or nearly minimal GRNs in all test problems.
Training a neural network for Gibbs and noise removal in diffusion MRI

Purpose To develop and evaluate a neural network-based method for Gibbs artifact and noise removal. Methods A convolutional neural network (CNN) was designed for artifact removal in diffusion-weighted imaging data. Two implementations were considered: one for magnitude images and one for complex images. Both models were based on the same encoder-decoder structure and were trained by simulating MRI acquisitions on synthetic non-MRI images. Results Both machine learning methods were able to mitigate artifacts in diffusion-weighted images and diffusion parameter maps. The CNN for complex images was also able to reduce artifacts in partial Fourier acquisitions. Conclusions The proposed CNNs extend the ability of artifact correction in diffusion MRI. The machine learning method described here can be applied on each imaging slice independently, allowing it to be used flexibly in clinical applications.
Kubo–Greenwood approach to conductivity in dense plasmas with average atom models

Abstract A new formulation of the Kubo–Greenwood conductivity for average atom models is given. The new formulation improves upon previous treatments by explicitly including the ionic-structure factor. Calculations based on this new expression lead to much improved agreement with ab initio results for DC conductivity of warm dense hydrogen and beryllium, and for thermal conductivity of hydrogen. We also give and test a slightly modified Ziman–Evans formula for the resistivity that includes a non-free electron density of states, thus removing an ambiguity in the original Ziman–Evans formula. Again, results based on this expression are in good agreement with ab initio simulations for warm dense beryllium and hydrogen. However, for both these expressions, calculations of the electrical conductivity of warm dense aluminum lead to poor agreement at low temperatures compared to ab initio simulations.
Categorified canonical bases and framed BPS states

We consider a cluster variety associated to a triangulated surface without punctures. The algebra of regular functions on this cluster variety possesses a canonical vector space basis parametrized by certain measured laminations on the surface. To each lamination, we associate a graded vector space, and we prove that the graded dimension of this vector space gives the expansion in cluster coordinates of the corresponding basis element. We discuss the relation to framed BPS states in $${\mathcal {N}}=2$$ field theories of class $${\mathcal {S}}$$.
Vacuum non-expanding horizons and shear-free null geodesic congruences

We investigate the geometry of a particular class of null surfaces in spacetime called vacuum non-expanding horizons (NEHs). Using the spin-coefficient equation, we provide a complete description of the horizon geometry, as well as fixing a canonical choice of null tetrad and coordinates on a NEH. By looking for particular classes of null geodesic congruences which live exterior to NEHs but have the special property that their shear vanishes at the intersection with the horizon, a good cut formalism for NEHs is developed which closely mirrors asymptotic theory. In particular, we show that such null geodesic congruences are generated by arbitrary choice of a complex worldline in a complex four-dimensional space, each such choice induces a CR structure on the horizon, and a particular worldline (and hence CR structure) may be chosen by transforming to a privileged tetrad frame.
Unitary Thermodynamics from Thermodynamic Geometry II: Fit to a Local-Density Approximation

Strongly interacting Fermi gasses at low density possess universal thermodynamic properties that have recently seen very precise PVT measurements by a group at MIT. This group determined local thermodynamic properties of a system of ultracold $$^6\text{ Li }$$ atoms tuned to Feshbach resonance. In this paper, I analyze the MIT data with a thermodynamic theory of unitary thermodynamics based on ideas from critical phenomena. This theory was introduced in the first paper of this sequence and characterizes the scaled thermodynamics by the entropy per particle $$z= S/N k_B$$ and the energy per particle Y(z), in units of the Fermi energy. Y(z) is in two segments, separated by a second-order phase transition at $$z=z_c$$ : a “superfluid” segment for $$z<z_c$$ and a “normal” segment for $$z>z_c$$ . For small z, the theory obeys a series $$Y(z)=y_0+y_1 z^{\alpha }+y_2 z^{2 \alpha }+\cdots ,$$ where $$\alpha $$ is a constant exponent and $$y_i$$ ( $$i\ge 0$$ ) are constant series coefficients. For large z, the theory obeys a perturbation of the ideal gas $$Y(z)= \tilde{y}_0\,\text{ exp }[2\gamma z/3]+ \tilde{y}_1\,\text{ exp }[(2\gamma /3-1)z]+ \tilde{y}_2\,\text{ exp }[(2\gamma /3-2)z]+\cdots $$ , where $$\gamma $$ is a constant exponent and $$\tilde{y}_i$$ ( $$i\ge 0$$ ) are constant series coefficients. This limiting form for large z differs from the series used in the first paper and was necessary to fit the MIT data. I fit the MIT data by adjusting four free independent theory parameters: $$(\alpha ,\gamma ,\tilde{y}_0,\tilde{y}_1)$$ . This fit process was augmented by trap integration and comparison with earlier thermal data taken at Duke University. The overall match to both the data sets was good and had $$\alpha =1.21(3)$$ , $$\gamma =1.21(3)$$ , $$z_c=0.69(2)$$ , scaled critical temperature $$T_c/T_F=0.161(3)$$ , where $$T_F$$ is the Fermi temperature, and Bertsch parameter $$\xi _B=0.368(5)$$ . I also discuss the virial expansion in the context of this thermodynamic geometric theory.
Chiral determinant on the lattice - anomalies and instantons

Abstract An expression for the lattice effective action induced by chiral fermions in any even dimensions in terms of an overlap of two states is shown to have promising properties in two and four dimensions: The correct abelian anomaly is reproduced andgauge field configurations with non-zero topological charge are completely suppressed.
TED: A Pretrained Unsupervised Summarization Model with Theme Modeling and Denoising

Text summarization aims to extract essential information from a piece of text and transform the text into a concise version. Existing unsupervised abstractive summarization models leverage recurrent neural networks framework while the recently proposed transformer exhibits much more capability. Moreover, most of previous summarization models ignore abundant unlabeled corpora resources available for pretraining. In order to address these issues, we propose TED, a transformer-based unsupervised abstractive summarization system with pretraining on large-scale data. We first leverage the lead bias in news articles to pretrain the model on millions of unlabeled corpora. Next, we finetune TED on target domains through theme modeling and a denoising autoencoder to enhance the quality of generated summaries. Notably, TED outperforms all unsupervised abstractive baselines on NYT, CNN/DM and English Gigaword datasets with various document styles. Further analysis shows that the summaries generated by TED are highly abstractive, and each component in the objective function of TED is highly effective.
The design and operation of the Keck Observatory archive

The Infrared Processing and Analysis Center (IPAC) and the W. M. Keck Observatory (WMKO) operate an archive for the Keck Observatory. At the end of 2013, KOA completed the ingestion of data from all eight active observatory instruments. KOA will continue to ingest all newly obtained observations, at an anticipated volume of 4 TB per year. The data are transmitted electronically from WMKO to IPAC for storage and curation. Access to data is governed by a data use policy, and approximately two-thirds of the data in the archive are public.
Two-dimensional partially ionized magnetohydrodynamic turbulence

Ionization occurs in the upper atmospheres of hot Jupiters and in the interiors of gas giant planets, leading to magnetohydrodynamic (MHD) effects that couple the momentum and the magnetic field, thereby significantly altering the dynamics. In regions of moderate temperatures, the gas is only partially ionized, which also leads to interactions with neutral molecules. To explore the turbulent dynamics of these regions, we utilize partially ionized magnetohydrodynamics (PIMHD), a two-fluid model – one neutral and one ionized – coupled by a collision term proportional to the difference in velocities. Motivated by planetary settings where rotation constrains the large-scale motions to be mostly two-dimensional, we perform a suite of simulations to examine the parameter space of two-dimensional PIMHD turbulence and pay particular attention to collisions and their role in the dynamics, dissipation and energy exchange between the two species. We arrive at, and numerically confirm, an expression for the energy loss due to collisions in both the weakly and strongly collisional limits, and show that, in the latter limit, the neutral fluid couples to the ions and behaves as an MHD fluid. Finally, we discuss some implications of our findings to current understanding of gas giant planet atmospheres.
Inference for modulated stationary processes

We study statistical inferences for a class of modulated stationary processes with time-dependent variances. Due to non-stationarity and the large number of unknown parameters, existing methods for stationary or locally stationary time series are not applicable. Based on a self-normalization technique, we address several inference problems, including self-normalized central limit theorem, self-normalized cumulative sum test for the change-point problem, long-run variance estimation through blockwise self-normalization, and self-normalization-based wild boot-strap. Monte Carlo simulation studies show that the proposed self-normalization-based methods outperform stationarity-based alternatives. We demonstrate the proposed methodology using two real data sets: annual mean precipitation rates in Seoul during 1771–2000, and quarterly U.S. Gross National Product growth rates during 1947–2002.
Quantum theory of structured monochromatic light

Applications that envisage utilizing the orbital angular momentum (OAM) at the single photon level assume that the OAM degrees of freedom of the photons are orthogonal. To test this critical assumption, we quantize the beam-like solutions of the vector Helmholtz equation from first principles. We show that although the photon operators of a diffracting monochromatic beam do not in general satisfy the canonical commutation relations, implying that the photon states in Fock space are not orthogonal, the states are bona fide eigenstates of the number and Hamiltonian operators. As a result, the representation for the photon operators presented in this work form a natural basis to study structured monochromatic light at the single photon level.