ShantanuT01/DACTYL-Pretraining huggingface dataset:
Models of stellar structure and evolution are an indispensable tool in astrophysics, yet they are known to incorrectly reproduce the outer convective layers of stars. In the first paper of this series, we presented a novel procedure to include the mean structure of 3D hydrodynamical simulations on-the-fly in stellar models, and found it to significantly improve the outer stratification and oscillation frequencies of a standard solar model. In the present work, we extend the analysis of the method; specifically how the transition point between envelope and interior affects the models. We confirm the versatility of our method by successfully repeating the entire procedure for a different grid of 3D hydro-simulations. Furthermore, the applicability of the procedure was investigated across the HR diagram and an accuracy comparable to the solar case was found. Moreover, we explored the implications on stellar evolution and find that the red-giant branch is shifted about 40 K to higher effective temperatures. Finally, we present for the first time an asteroseismic analysis based on stellar models fully utilising the stratification of 3D simulations on-the-fly. These new models significantly reduce the asteroseismic surface term for the two selected stars in the Kepler field. We extend the analysis to red giants and characterise the shape of the surface effect in this regime. Lastly, we stress that the interpolation required by our method would benefit from new 3D simulations, resulting in a finer sampling of the grid.
In a series of recent papers, it has been proposed that high field magnetic white dwarfs are the result of close binary interaction and merging. Population synthesis calculations have shown that the origin of isolated highly magnetic white dwarfs is consistent with the stellar merging hypothesis. In this picture, the observed fields are caused by an alpha-Omega dynamo driven by differential rotation. The strongest fields arise when the differential rotation equals the critical break-up velocity and result from the merging of two stars (one of which has a degenerate core) during common envelope evolution or from the merging of two white dwarfs. We now synthesise a population of binary systems to investigate the hypothesis that the magnetic fields in the magnetic cataclysmic variables also originate during stellar interaction in the common envelope phase. Those systems that emerge from common envelope more tightly bound form the cataclysmic variables with the strongest magnetic fields. We vary the common envelope efficiency parameter and compare the results of our population syntheses with observations of magnetic cataclysmic variables. We find that common envelope interaction can explain the observed characteristics of these magnetic systems if the envelope ejection efficiency is low.
Transformer-based models, such as the Vision Transformer (ViT), can outperform onvolutional Neural Networks (CNNs) in some vision tasks when there is sufficient training data. However, (CNNs) have a strong and useful inductive bias for vision tasks (i.e. translation equivariance and locality). In this work, we developed a novel model architecture that we call a Mobile fish landmark detection network (MFLD-net). We have made this model using convolution operations based on ViT (i.e. Patch embeddings, Multi-Layer Perceptrons). MFLD-net can achieve competitive or better results in low data regimes while being lightweight and therefore suitable for embedded and mobile devices. Furthermore, we show that MFLD-net can achieve keypoint (landmark) estimation accuracies on-par or even better than some of the state-of-the-art (CNNs) on a fish image dataset. Additionally, unlike ViT, MFLD-net does not need a pre-trained model and can generalise well when trained on a small dataset. We provide quantitative and qualitative results that demonstrate the model's generalisation capabilities. This work will provide a foundation for future efforts in developing mobile, but efficient fish monitoring systems and devices.
Magnetic graphene-ribbon is a candidate for realizing future ultra high density 100 tera bit/inch2 class data storage media. Multiple spin state analysis was done based on the density function theory. A typical model was a super cell [C80H7] which having bare (radical) carbons on one side zigzag edge, whereas mono hydrogenated on another side. Optimizing atomic configuration, self consistent calculation demonstrated that a total energy of the highest spin state is more stable than that of lower one, which came from exchange coupling between carbons. This analysis suggested a capability of designing magnetic data track utilizing such chemically edge modified graphene ribbon. In order to increase areal magnetization density, bilayer and quadri-layer graphene-ribbon model were analyzed. Detailed calculation resulted that also the highest spin state is the most stable one. Multiplying the layer numbers is effective way to realize and enhance strong magnetism.
GRB afterglows are well suited to extinction studies due to their brightness, simple power-law spectra and the occurrence of GRBs in distant star forming galaxies. In this paper we present results from the SED analysis of a sample of 41 GRB afterglows, from X-ray to NIR wavelengths. This is the largest sample of extinction curves outside the Local Group and, to date, the only extragalactic sample of absolute extinction curves based on spectroscopy. Visual extinction correlation with HI column density as well as total and gas-phase metal column density are examined. Approximately half the sample require a cooling break between the optical and X-ray regimes. The broken power-law SEDs show an average change in the spectral index of delta_beta=0.51 with a standard deviation of 0.02. This is consistent with the expectation from a simple synchrotron model. Of the sample, 63% are well described by the SMC-type extinction curve and have moderate or low extinction, with AV<0.65. Almost a quarter of our sample is consistent with no significant extinction (typically AV<0.1). The 2175AA extinction bump is detected unequivocally in 7% of our sample (3 GRBs), which all have A_V>1.0. We find an anti-correlation between gas-to-dust ratio and metallicity consistent with the Local Group relation. Our metals-to-dust ratios derived from the soft X-ray absorption are always larger (3-30 times) than the Local Group value, which may mean that GRB hosts may be less efficient at turning their metals into dust. However, we find that gas, dust, and metal column densities are all likely to be influenced by photo-ionization and dust destruction effects from the GRB. [abridged]
We show that Hermite's approximations to values of the exponential function at given algebraic numbers are nearly optimal when considered from an adelic perspective. We achieve this by taking into account the ratio of these values whenever they make sense in the various completions (Archimedean or $p$-adic) of a number field containing these algebraic numbers.
In this paper we prove a sparse equidistribution theorem for Gross points over the rational function field $\mathbb{F}_q(t)$. We apply this result to study the reduction map from CM Drinfeld modules to supersingular Drinfeld modules. Our proofs rely crucially on a period formula due to M. Papikian and F.-T. Wei/J. Yu, and a Lindel\"of-type bound for central values of Rankin-Selberg $L$-functions associated to twists of automorphic forms of Drinfeld-type by ideal class group characters.
Explosions of sub-Chandrasekhar-mass white dwarfs are one alternative to the standard Chandrasekhar-mass model of Type Ia supernovae. They are interesting since binary systems with sub-Chandrasekhar-mass primary white dwarfs should be common and this scenario would suggest a simple physical parameter which determines the explosion brightness, namely the mass of the exploding white dwarf. Here we perform one-dimensional hydrodynamical simulations, associated post-processing nucleosynthesis and multi-wavelength radiation transport calculations for pure detonations of carbon-oxygen white dwarfs. The light curves and spectra we obtain from these simulations are in good agreement with observed properties of Type Ia supernovae. In particular, for white dwarf masses from 0.97 - 1.15 Msun we obtain 56Ni masses between 0.3 and 0.8 Msun, sufficient to capture almost the complete range of Type Ia supernova brightnesses. Our optical light curve rise times, peak colours and decline timescales display trends which are generally consistent with observed characteristics although the range of B-band decline timescales displayed by our current set of models is somewhat too narrow. In agreement with observations, the maximum light spectra of the models show clear features associated with intermediate mass elements and reproduce the sense of the observed correlation between explosion luminosity and the ratio of the Si II lines at 6355 and 5972 Angstroms. We therefore suggest that sub-Chandrasekhar mass explosions are a viable model for Type Ia supernovae for any binary evolution scenario leading to explosions in which the optical display is dominated by the material produced in a detonation of the primary white dwarf.
What happens to the entropy increase principle as the Universe evolve to form the big-crunch singularity? What happens to the uncertainity relations along the process of gravitational collapses? What is the quantum mechanical description of a Radon atom in a rigid box when the distance of consecutive nodes and antinodes of $\psi$ is equal to or less than the diameter of the atom? What is the position-space wave function of two finite volume massive bosons if we take contact interaction into account? How a photon produce electron-positron pair with finite volume concentrate rest masses? What are the charges of the electron-positron pairs forming loops in the vacuum? How two particles with three-momentums $k_1, k_2$ $(k_1 \neq k_2)$ produced to form a loop at a space-time point always arrive at another spacial point simultaneously? What is the microscopic explanation in terms of particle exchanges of the force in the Casimir effect? What is the mechanism of the collapse of the momentum-space wave function of a particle knocking out an elctron from an atom? What is meant by $|\Psi> = {c_1 (t)}|\Psi_{U^{238}}> + {c_2 (t)}|\Psi_{Th^{234}}> ~?$ Quantum mechanically the region between the rigid walls (which is equiprobable in classical mechanics) is non-homogeneous for a particle in a rigid box. A photon can not reproduce Maxwell's equations apart from moving with velocity $c$. How can a process involving only a few photons be described starting from the Maxwell's equations? The large scale structure of the Universe is homogeneous.   What is the screen in our brains to view objects, as they are, of sizes larger than our brains?
The study of Majorana fermions is of great importance for the implementation of a quantum computer. These modes are topologically protected and very stable. It is now well known that a p-wave superconducting wire can sustain, in its topological non-trivial phase, Majorana quasi-particles at its ends. Since this type of superconductor is not found in nature, many methods have been devised to implement it. Most of them rely on the spin-orbit interaction. In this paper we study the superconducting properties of a two-band system in the presence of antisymmetric hybridization. We consider inter-band attractive interactions and also an attractive interaction in one of the bands. We show that superconducting fluctuations with p-wave character are induced in the non-interacting band due to the combined effects of inter-band coupling and hybridization. In the case of a wire, this type of induced superconductivity gives rise to four Majorana modes at its ends. The long range correlation between the different charge states of these modes offers new possibilities for the implementation of protected q-bits.
We consider the $L^2$-critical nonlinear Schrodinger equation with an inhomogeneous damping term. We prove that there exists an initial data such that the corresponding solution is global in $H^1(R^d)$ and we give the minimal time of the blow up for some initial data.
Suppose that two distant parties Alice and Bob share an entangled state $\rho_{AB}$, and they want to exchange the subsystems of $\rho_{AB}$ by local operations and classical communication (LOCC). In general, this LOCC task (i.e. the LOCC transformation of $\rho_{AB} \to V\rho_{AB} V$ with $V$ being a swap operator) is impossible deterministically, but becomes possible probabilistically. In this paper, we study how the optimal probability is related to the amount of entanglement in the framework of positive partial transposed (PPT) operations, and numerically show a remarkable class of states whose probability is the smallest among every state in two quantum bits.
Spectral energy distributions (SEDs) are some of the most important sources of information for galaxies, especially for high redshift ones. Here we review recent work on the subject. We discuss the integrated spectra of galaxies of different morphological and activity type, their application to derive K-corrections and classification of high redshift objects. We also discuss the radio to X-rays SEDs of Seyfert 2's, Starbursts and normal galaxies, their behavior as a function of the waveband, their bolometric fluxes and the wavebands that contribute most to it.
I will show that Be stars are, without exception, a class of rapidly rotating stars, which are in the majority of cases pulsating stars as well, while none of them does possess a large scale (i.e. with significant dipolar contribution) magnetic field.
A spin dynamics algorithm, combining checkerboard updating and a rotation algorithm based on the local second-rank ordering field, is developed for the Lebwohl-Lasher model of liquid crystals. The method is shown to conserve energy well and to generate simulation averages which are consistent with those obtained by Monte Carlo simulation. However, care must be taken to avoid the undesirable effects of director rotation, and a method for doing this is proposed.
The paper studies the time-homogeneous two-state Markov chains; the states are assumed to be binary symbols 0 and 1. The higher-order absolute differences taken from progressive states of a given chain are considered. A discrete capacity of subsets of natural series is defined and a limiting theorem for these differences, formulated in terms of Wiener criterion type relation, is presented.
The aim of this paper is to deal with congruences for Jacobi sums of order $2l^{2}$ over a finite field $\mathbb{F}_{q}, q=p^{r}$, $p^{r}\equiv 1\ (mod \ 2l^{2})$, where $l>3$ and $p$ are primes. Further, we also calculate Jacobi sums $J_{2l^{2}}(1,n)$ of order $2l^{2}$ in terms of Dickson-Hurwitz sums.
aims: We study the recently discovered twisting motion of bright penumbral filaments with the aim of constraining their geometry and the associated magnetic field. methods: A large sunspot located $40\degr$ from disk center was observed at high resolution with the 1-m Swedish Solar Telescope. Inversions of multi-wavelength polarimetric data and speckle reconstructed time series of continuum images were used to determine proper motions, as well as the velocity and magnetic structure in penumbral filaments. results: The continuum movie reveals apparent lateral motions of bright and dark structures inside bright filaments oriented parallel to the limb, confirming recent Hinode results. In these filaments we measure upflows of $\approx 1.1 \mathrm{km/s}$ on their limbward side and weak downflows on their centerward side. The magnetic field in them is significantly weaker and more horizontal than in the adjacent dark filaments. conclusions: The data indicate the presence of vigorous convective rolls in filaments with a nearly horizontal magnetic field. These are separated by filaments harbouring stronger, more vertical fields. Because of reduced gas pressure, we see deeper into the latter. When observed near the limb, the disk-centerward side of the horizontal-field filaments appear bright due to the \textit{hot wall} effect known from faculae. We estimate that the convective rolls transport most of the energy needed to explain the penumbral radiative flux.
We investigate propagation of few-photon pulses in waveguides coupled to a two-level system by means of the method of distribution functions in coordinate-momentum space that provides a detailed description of photon systems. We find that the distribution function of the transmitted pulse can be negative for the nonclassical input (i.e., single-photon Fock state). This reveals the quasiprobability nature of photon distribution. Analytical expressions for photon densities in the momentum space as well as in the coordinate space are obtained for the mentioned single-photon Gaussian input. We also study evolution of the multimode coherent-state input for an arbitrary photon number. Time-dependent differential equations describing average densities and fluctuations of outgoing photons are derived and solved. Influence of the number of input photons, pulse width, and radiation-atom interaction strength on the statistical properties of the fluctuations is investigated.
We deal with the distribution of the fractional parts of $p^{\lambda}$, $p$ running over the prime numbers and $\lambda$ being a fixed real number lying in the interval $(0,1)$. Roughly speaking, we study the following question: Given a real $\theta$, how small may $\delta>0$ be choosen if we suppose that the number of primes $p\le N$ satisfying ${p^{\lambda}-\theta<\delta}$ is close to the expected one? We improve some results of Balog and Harman on this question for $\lambda<5/66$ if $\theta$ is rational and for $\lambda<1/5$ if $\theta$ is irrational.   Our improvement is based on incorporating the zero detection argument into Harman's method and on using new mean value estimates for products of shifted and ordinary (unshifted) Dirichlet polynomials.
Let $(M,g)$ be a four dimensional compact Riemannian manifold with boundary and $(N,h)$ be a compact Riemannian manifold without boundary. We show the existence of a unique, global weak solution of the heat flow of extrinsic biharmonic maps from $M$ to $N$ under the Dirichlet boundary condition, which is regular with the exception of at most finitely many time slices. We also discuss the behavior of solution near the singular times. As an immediate application, we prove the existence of a smooth extrinsic biharmonic map from $M$ to $N$ under any Dirichlet boundary condition.
We give a new proof of Makar-Limanov's theorem, which states that Russell's hypersurface is not isomorphic to affine three space.
In this paper we propose a novel method to study critical systems numerically by a combined collective-mode algorithm and Renormalization Group on the lattice. This method is an improved version of MCRG in the sense that it has all the advantages of cluster algorithms. As an application we considered the 2D Ising model and studied wether scale invariance or universality are possible underlying mechanisms responsible for the approximate "universal fluctuations" close to a so-called bulk temperature $T^*(L)$. "Universal fluctuations" was first proposed in [1] and stated that the probability density function of a global quantity for very dissimilar systems, like a confined turbulent flow and a 2D magnetic system, properly normalized to the first two moments, becomes similar to the "universal distribution", originally obtained for the magnetization in the 2D XY model in the low temperature region. The results for the critical exponents and the renormalization group flow of the probability density function are very accurate and show no evidence to support that the approximate common shape of the PDF should be related to both scale invariance or universal behavior.
Context. Some of the most dynamic active regions are associated with complex photospheric magnetic configurations such as quadrupolar regions, and especially ones with a $\delta$-spot configuration and a strong Polarity Inversion Line (PIL). Aims. We study the formation and eruption of magnetic flux ropes in quadrupolar regions. Methods. 3D MHD simulations of the partial emergence of a highly twisted flux tube from the solar interior into a non-magnetized stratified atmosphere. Results. We emerge two $\Omega$-shaped loops forming a quadrupolar region. The emerging flux forms two initially separated bipoles, that later come in contact creating a $\delta$-spot central region. Above the two bipoles, two magnetic lobes expand and interact through a series of current sheets at the interface between them. Two recurrent confined eruptions are produced. In both cases, reconnection between sheared low-lying field lines forms a flux rope. Reconnection between the two lobes high in the atmosphere forms retracting field lines that push against the flux rope, creating a current sheet between them. It also forms a third magnetic lobe between the two emerged ones, that later acts as a strapping field. The flux rope eruptions are triggered when the reconnection between the flux ropes and the field above them becomes efficient enough to remove the tension of the overlying field. These reconnection events occur internally in the system. The first erupting flux rope almost fully reconnects with the overlying field. The second eruption is confined by the overlying field. During the confined eruption, the flux rope is enhanced in size, flux and twist, similar to confined-flare-to-flux-rope observations. Proxies of the emission reveal the two erupting filaments channels. A flare arcade is formed only in the second eruption due to the longer-lasting and more efficient reconnection below the flux rope.
The power sum $1^n + 2^n + \cdots + x^n$ has been of interest to mathematicians since classical times. Johann Faulhaber, Jacob Bernoulli, and others who followed expressed power sums as polynomials in $x$ of degree $n+1$ with rational coefficients. Here we consider the denominators of these polynomials, and prove some of their properties. A remarkable one is that such a denominator equals $n+1$ times the squarefree product of certain primes $p$ obeying the condition that the sum of the base-$p$ digits of $n+1$ is at least $p$. As an application, we derive a squarefree product formula for the denominators of the Bernoulli polynomials.
Two examples of Microcanonical Potts models, 2-dimensional nearest neighbor and mean field, are considered via exact enumeration of states and analytical asymptotic methods. In the interval of energies corresponding to a first order phase transition, both of these models exhibit a convex dip in the entropy vs energy plot and a region with negative specific heat within the dip. It is observed that in the nearest neighbor model the dip flattens and disappears as the lattice size grows, while in the mean field model the dip persists even in the limit of an infinite system. If formal transitions from microcanonical to canonical ensembles and back are performed for an infinite but non-extensive system, the convex dip in the microcanonical entropy plot disappears.
A new hybrid scheme for numerical relativity will be presented. The scheme will employ a 3-dimensional spacelike lattice to record the 3-metric while using the standard 3+1 ADM equations to evolve the lattice. Each time step will involve three basic steps. First, the coordinate quantities such as the Riemann and extrinsic curvatures are extracted from the lattice. Second, the 3+1 ADM equations are used to evolve the coordinate data, and finally, the coordinate data is used to update the scalar data on the lattice (such as the leg lengths). The scheme will be presented only for the case of vacuum spacetime though there is no reason why it could not be extended to non-vacuum spacetimes. The scheme allows any choice for the lapse function and shift vectors. An example for the Kasner $T^3$ cosmology will be presented and it will be shown that the method has, for this simple example, zero discretisation error.