ShantanuT01/DACTYL-Pretraining huggingface dataset:
We present a theoretical study of the effects and signatures of realistic velocity field and atmospheric inhomogeneities associated with convective motions at the surface of cool late-type stars on the emergent profiles of iron spectral lines for a large range in stellar parameters. We compute 3D spectral line flux profiles under the assumption of local thermodynamic equilibrium (LTE) by employing state-of-the-art, time-dependent, 3D, radiative-hydrodynamical atmosphere models from the Stagger-grid. A set of 35 real unblended, optical FeI and FeII lines of varying excitation potential are considered. Additionally, fictitious Fe i and Fe ii lines (5000A and 0, 2, 4 eV) are used to construct general curves of growth and enable comparison of line profiles with the same line strength to illustrate systematical trends stemming from the intrinsic structural differences among 3D model atmospheres with different stellar parameters. Theoretical line shifts and bisectors are derived to analyze the shapes, shifts, and asymmetries imprinted in the full 3D line profiles emerging self-consistently from the convective simulations with velocity fields and atmospheric inhomogeneities. We find systematic variations in line strength, shift, width, and bisectors, that can be related to the respective physical conditions at the height of the line formation in the stellar atmospheric environment, in particular the amplitude of the vertical velocity field. Line shifts and asymmetries arise due to the presence of convective velocities and the granulation pattern that are ubiquitously found in observed stellar spectra of cool stars.
[abridged] Previous analyses of lithium abundances in main sequence and red giant stars have revealed the action of mixing mechanisms other than convection in stellar interiors. Beryllium abundances in stars with lithium abundance determinations can offer valuable complementary information on the nature of these mechanisms. Our aim is to derive beryllium abundances along the whole evolutionary sequence of an open cluster, IC 4651. These Be abundances are used together with previously determined Li abundances, in the same sample stars, to investigate the mixing mechanisms in a range of stellar masses and evolutionary stages. New beryllium abundances are determined from high-resolution, high signal-to-noise UVES spectra using spectrum synthesis and model atmospheres. The careful synthetic modelling of the Be lines region is used to calculate reliable abundances in rapidly rotating stars. The observed behavior of Be and Li is compared to theoretical predictions from stellar models including rotation-induced mixing, internal gravity waves, atomic diffusion, and thermohaline mixing. Beryllium is detected in all the main sequence and turn-off sample stars, both slow- and fast-rotating stars, including the Li-dip stars, but was not detected in the red giants. Confirming previous results, we find that the Li dip is also a Be dip, although the depletion of Be is more modest than that of Li in the corresponding effective temperature range. For post-main-sequence stars, the Be dilution starts earlier within the Hertzsprung gap than expected from classical predictions as does the Li dilution. A clear dispersion in the Be abundances is also observed. Theoretical stellar models including the hydrodynamical transport processes mentioned above are able to reproduce well all the observed features.
X-shaped radio galaxies are defined by their peculiar large-scale radio morphology. In addition to the classical double-lobed structure they have a pair of low-luminosity wings that straddles the nucleus at almost right angles to the active lobes, thus giving the impression of an 'X'. In this paper we study for the first time the optical spectral properties of this object class using a large sample (~50 sources). We find that the X-shaped radio population is composed roughly equally of sources with weak and strong emission line spectra, which makes them, in combination with the well-known fact that they preferentially have radio powers intermediate between those of Fanaroff-Riley type I (FR I) and type II (FR II) radio galaxies, the archetypal transition population. We do not find evidence in support of the proposition that the X-shape is the result of a recent merger: X-shaped radio sources do not have unusually broad emission lines, their nuclear environments are in general not dusty, and their host galaxies do not show signs of enhanced star formation. Instead, we observe that the nuclear regions of X-shaped radio sources have relatively high temperatures. This finding favours models, which propose that the X-shape is the result of an overpressured environment.
The SUrvey for Pulsars and Extragalactic Radio Bursts ran from 2014 April to 2019 August, covering a large fraction of the southern hemisphere at mid- to high-galactic latitudes, and consisting of 9-minute pointings taken with the 20-cm multibeam receiver on the Parkes Radio Telescope. Data up to 2017 September 21 have been searched using standard Fourier techniques, single-pulse searches, and Fast Folding Algorithm searches. We present 19 new discoveries, bringing the total to 27 discoveries in the programme, and we report the results of follow-up timing observations at Parkes for 26 of these pulsars, including the millisecond pulsar PSR J1421-4409; the faint, highly-modulated, slow pulsar PSR J1646-1910; and the nulling pulsar PSR J1337-4441. We present new timing solutions for 23 pulsars, and we report flux densities, modulation indices, and polarization properties.
The Maximum Degree and Diameter Bounded Subgraph Problem (MaxDDBS) asks: given a host graph G, a bound on maximum degree \Delta, and a diameter D, what is the largest subgraph of the host graph with degree bounded by \Delta and diameter bounded by D? In this paper, we investigate this problem when the host graph is the k-dimensional mesh. We provide lower bounds for the size of the largest subgraph of the mesh satisfying MaxDDBS for all k and \Delta > 3 that agree with the known upper bounds up to the first two terms, and show that for \Delta = 3, the lower bounds are at least the same order of growth as the upper bounds.
This paper aims to precisely determine the masses and detect pulsation modes in the two massive components of Beta Cen with BRITE-Constellation photometry. In addition, seismic models for the components are considered and the effects of fast rotation are discussed. This is done to test the limitations of seismic modeling for this very difficult case. A simultaneous fit of visual and spectroscopic orbits is used to self-consistently derive the orbital parameters, and subsequently the masses, of the components. The derived masses are equal to 12.02 +/- 0.13 and 10.58 +/- 0.18 M_Sun. The parameters of the wider, A - B system, presently approaching periastron passage, are constrained. Analysis of the combined blue- and red-filter BRITE-Constellation photometric data of the system revealed the presence of 19 periodic terms, of which eight are likely g modes, nine are p modes, and the remaining two are combination terms. It cannot be excluded that one or two low-frequency terms are rotational frequencies. It is possible that both components of Beta Cen are Beta Cep/SPB hybrids. An attempt to use the apparent changes of frequency to distinguish which modes originate in which component did not succeed, but there is potential for using this method when more BRITE data become available. Agena seems to be one of very few rapidly rotating massive objects with rich p- and g-mode spectra, and precisely known masses. It can therefore be used to gain a better understanding of the excitation of pulsations in relatively rapidly rotating stars and their seismic modeling. Finally, this case illustrates the potential of BRITE-Constellation data for the detection of rich-frequency spectra of small-amplitude modes in massive pulsating stars.
We present the perturbation theory for lattice magnon fields of $D$-dimensional O(3) Heisenberg ferromagnet. The effective Hamiltonian for the lattice magnon fields is obtained starting from the effective Lagrangian, with two dominant contributions that describe magnon-magnon interactions identified as a usual gradient term for the unit vector field and a part originating in the Wess-Zumino-Witten term of effective Lagrangian. Feynman diagrams for lattice scalar fields with derivative couplings are introduced, on basis of which we investigate the influence of magnon-magnon interactions on magnon self-energy and ferromagnet free energy. We also comment appearance of spurious terms in the low-temperature series for the free energy by examining magnon-magnon interactions and internal symmetry of the effective Hamiltonian (Lagrangian).
Recent studies about collisionless shocks in partially ionized plasmas showed that some of neutral particles leak into the shock upstream region from the downstream region. In this paper, we perform a linear analysis and show that acoustic waves are unstable in the neutral precursor region. The acoustic instability amplifies fluctuations of magnetic field and density in the upstream region. The fluctuations are indispensable for the diffusive shock acceleration and could be important for the downstream turbulence.
Unsupervised image-to-image translation aims at learning a mapping between two visual domains. However, learning a translation across large geometry variations always ends up with failure. In this work, we present a novel disentangle-and-translate framework to tackle the complex objects image-to-image translation task. Instead of learning the mapping on the image space directly, we disentangle image space into a Cartesian product of the appearance and the geometry latent spaces. Specifically, we first introduce a geometry prior loss and a conditional VAE loss to encourage the network to learn independent but complementary representations. The translation is then built on appearance and geometry space separately. Extensive experiments demonstrate the superior performance of our method to other state-of-the-art approaches, especially in the challenging near-rigid and non-rigid objects translation tasks. In addition, by taking different exemplars as the appearance references, our method also supports multimodal translation. Project page: https://wywu.github.io/projects/TGaGa/TGaGa.html
In this paper we study ergodic backward stochastic differential equations (EBSDEs) dropping the strong dissipativity assumption needed in the previous work. In other words we do not need to require the uniform exponential decay of the difference of two solutions of the underlying forward equation, which, on the contrary, is assumed to be non degenerate. We show existence of solutions by use of coupling estimates for a non-degenerate forward stochastic differential equations with bounded measurable non-linearity. Moreover we prove uniqueness of "Markovian" solutions exploiting the recurrence of the same class of forward equations. Applications are then given to the optimal ergodic control of stochastic partial differential equations and to the associated ergodic Hamilton-Jacobi-Bellman equations.
We study the dimensional crossover from 2D to 1D type behavior, which takes place in the thermal excited rippling of a graphene honeycomb lattice, when one of the dimensions of the layer is reduced. Through a joint study, by Monte Carlo (MC) atomistic simulations using a quasi-harmonic potential and analytical calculations, we find that the normal-normal correlation function does not change its power law behavior in the long wavelength limit. However the system size dependency of the square of out of plane displacement $ <h^2>$ changes its scaling behavior when going from a layer to a nanoribbon. We show that a new scaling law appears which corresponds to a truly 1D behavior and we estimate the ratio of the sample dimensions where the crossover takes place as $R_{2D \leftrightarrow 1D}\approx 1.609$. Having explored a wide number of realistic systems sizes, we conclude that narrow ribbons present stronger corrugations than the square graphene sheets and we discuss the implications for the electronic properties of freestanding graphene systems.
Within a perturbative approach to Quantum Chromodynamics (QCD), we show how to extend ordinary DGLAP longitudinal evolution equations to include the radiative transverse momentum generated in the collinear branching regime. Considering Semi-inclusive Deep Inelastic Scattering as a reference process, we perform such a generalization both in the current and in the target fragmentation region. These distributions are then used to predict semi-inclusive Deep Inelastic Scattering cross-sections onto the whole phase space of the detected hadron.
We review the history and the current status of the understanding of the processes that regulate Lyman alpha emission from star-forming galaxies. We present some of the most recent results of our study to image local starburst galaxies in the Lyman alpha emission line using the Advanced Camera for Surveys on the Hubble Space Telescope. Particular attention is dedicated to our study of the low-metallicity, dust-poor Blue Compact Galaxy ESO338-IG04. We discuss some of our local observational results with reference to the interpretation of results of high-redshift Lyman alpha surveys and recent simulations of the detection properties of high-z Lyman alpha emitting objects performed by our group.
The discovery of jets from tidal disruption events (TDEs) rejuvenated the old field of relativistic jets powered by accretion onto supermassive black holes. In this Chapter, we first review the extensive multi-wavelength observations of jetted TDEs. Then, we show that these events provide valuable information on many aspects of jet physics from a new prospective, including the on-and-off switch of jet launching, jet propagation through the ambient medium, $\gamma/$X-ray radiation mechanism, jet composition, and the multi-messenger picture. Finally, open questions and future prospects in this field are summarized.
The atmospheres of novae at early times in their outbursts are very extended, expanding shells with low densities. Models of these atmospheres show that NLTE effects are very important and must be included in realistic calculations. We have, therefore, been improving our atmospheric studies by increasing the number of ions treated in NLTE. One of the most important ions is Fe II which has a complex structure and numerous lines in the observable spectrum. In this paper we investigate NLTE effects for Fe II for a wide variety of parameters. We use a detailed Fe II model atom with 617 level and 13675 primary lines, treated using a rate-operator formalism. We show that the radiative transfer equation in nova atmospheres {\em must} be treated with sophisticated numerical methods and that simple approximations, such as the Sobolev method, {\em cannot} be used because of the large number of overlapping lines in the co-moving frame.   Our results show that the formation of the Fe II lines is strongly affected by NLTE effects. For low effective temperatures, $\Teff < 20,000\,$K, the optical Fe II lines are most influenced by NLTE effects, while for higher $\Teff$ the UV lines of Fe II are very strongly affected by NLTE. The departure coefficients are such that Fe II tends to be overionized in NLTE when compared to LTE. Therefore, Fe II-NLTE must be included with sophisticated radiative transfer in nova atmosphere models in order to reliably analyze observed nova spectra.
We are studying the impact of HII regions on star formation in their associated molecular clouds. In this paper we present JCMT RxA molecular line observations of S175 and environs. This is the first within a sample of ten HII regions and their surrounding molecular clouds selected for our study. We first make 7'x 7' maps in $^{12}$CO(2-1), which are used to investigate the structure of the cloud and to identify individual clumps. Single point observations were made in $^{13}$CO(2-1) and CS(5-4) at the peak of the $^{12}$CO(2-1) emission within each clump in order to measure the physical properties of the gas. Densities, temperatures, clump masses, peak velocities, and line widths were measured and calculated using these observations. We have identified two condensations (S175A and S175B) in the molecular cloud associated with this HII region. S175A is adjacent to the ionization front and is expected to be affected by the HII region while S175B is too distant to be disturbed. We compare the structure and gas properties of these two regions to investigate how the molecular gas has been affected by the HII region.   S175A has been heated by the HII region and partially compressed by the ionized gas front, but contrary to our expectation it is a quiescent region while S175B is very turbulent and dynamically active. Our investigation for the source of turbulence in S175B resulted in the detection of an outflow within this region.
Spatially averaged (> 50'') EUV spectral lines in the transition region of solar quiet regions are known to be redshifted. Because the mechanism underlying this phenomenon is unclear, we require additional physical information on the lower corona for limiting the theoretical models. To acquire this information, we measured the Doppler shifts over a wide coronal temperature range (log T[K]=5.7--6.3) using the spectroscopic data taken by the Hinode EUV Imaging Spectrometer. By analyzing the data over the center-to-limb variations covering the meridian from the south to the north pole, we successfully measured the velocity to an accuracy of 3 km/s. Below log T[K] = 6.0, the Doppler shifts of the emission lines were almost zero with an error of 1--3 km/s; above this temperature, they were blueshifted with a gradually increasing magnitude, reaching - 6.3 +/- 2.1 km/s at log T[K]=6.25.
If the fourth generation fermions exist, the new quarks could influence the branching ratios of the decays of $B\to X_s \gamma$ and $B\to X_sl^+l^-$. We obtain two solutions of the fourth generation CKM factor $V^{*}_{t^{'}s}V_{t^{'}b}$ from the decay of $B\to X_s \gamma$. We use these two solutions to calculate the new contributions of the fourth generation quark to Wilson coefficients of the decay of $B\to X_sl^+l^-$. The branching ratio and the forward-backward asymmetry of the decay of $B\to X_sl^+l^-$ in the two cases are calculated. Our results are quite different from that of SM in one case, almost same in another case. If Nature chooses the formmer, the $B$ meson decays could provide a possible test of the forth generation existence.
We present the latest developments of the MadGraph/MadEvent Monte Carlo event generator and several applications to hadron collider physics. In the current version events at the parton, hadron and detector level can be generated directly from a web interface, for arbitrary processes in the Standard Model and in several physics scenarios beyond it (HEFT, MSSM, 2HDM). The most important additions are: a new framework for implementing user-defined new physics models; a standalone running mode for creating and testing matrix elements; generation of events corresponding to different processes, such as signal(s) and backgrounds, in the same run; two platforms for data analysis, where events are accessible at the parton, hadron and detector level; and the generation of inclusive multi-jet samples by combining parton-level events with parton showers. To illustrate the new capabilities of the package some applications to hadron collider physics are presented:   1) Higgs search in pp \to H \to W^+W^-: signal and backgrounds.   2) Higgs CP properties: pp \to H jj$in the HEFT.   3) Spin of a new resonance from lepton angular distributions.   4) Single-top and Higgs associated production in a generic 2HDM.   5) Comparison of strong SUSY pair production at the SPS points.   6) Inclusive W+jets matched samples: comparison with the Tevatron data.
We prove, using variational methods, the existence in dimension two of positive vector ground states solutions for the Bose-Einstein type systems \begin{equation} \begin{cases} -\Delta u+\lambda_1u=\mu_1u(e^{u^2}-1)+\beta v\left(e^{uv}-1\right) \text{ in } \Omega, &\\ -\Delta v+\lambda_2v=\mu_2v(e^{v^2}-1)+\beta u\left(e^{uv}-1\right)\text{ in } \Omega, &\\ u,v\in H^1_0(\Omega) \end{cases} \end{equation} where $\Omega$ is a bounded smooth domain, $\lambda_1,\lambda_2>-\Lambda_1$ (the first eigenvalue of $(-\Delta,H^1_0(\Omega))$, $\mu_1,\mu_2>0$ and $\beta$ is either positive (small or large) or negative (small). The nonlinear interaction between two Bose fluids is assumed to be of critical exponential type in the sense of J. Moser. For `small' solutions the system is asymptotically equivalent to the corresponding one in higher dimensions with power-like nonlinearities.
A comparative study of the non-equilibrium magnetic phenomena (magnetic blocking, memory, exchange bias and aging effect) has been presented for ferrimagnetic Co$_{1.75}$Fe$_{1.25}$O$_4$ (CFO) and its composite with non-magnetic BaTiO$_3$ (BTO). Synchrotron X-Ray diffraction patterns have confirmed coexistence of CFO and BTO structures in composite, but magnetic spin dynamics have been remarkably modified. The blocking phenomenon of ferrimagnetic domains below the room temperature has been studied by different modes of (zero field cooled and field cooled) magnetic measurements in collaboration with magnetic fields ON and OFF modes and time dependent magnetization. The applications of unconventional protocols during time dependent magnetization measurement at different stages of the temperature and field dependence of the magnetization curves have been useful to reveal the non-equilibrium dynamics of magnetic spin order. The applying of off-field relaxation experiments has made possible to tune the magnetic state and coercivity of the systems. The role of interfacial coupling between magnetic and non-magnetic particles has been understood on different magnetic phenomena (meta-stable magnetic state, exchange bias and memory effect) by comparing the experimental results of Co$_{1.75}$Fe$_{1.25}$O$_4$ spinel oxide and its composite with BaTiO$_3$ particles.
We investigate in this note the dynamics of a one-dimensional Keller-Segel type model on the half-line. On the contrary to the classical configuration, the chemical production term is located on the boundary. We prove, under suitable assumptions, the following dichotomy which is reminiscent of the two-dimensional Keller-Segel system. Solutions are global if the mass is below the critical mass, they blow-up in finite time above the critical mass, and they converge to some equilibrium at the critical mass. Entropy techniques are presented which aim at providing quantitative convergence results for the subcritical case. This note is completed with a brief introduction to a more realistic model (still one-dimensional).
Phase transitions generically occur in random matrix models as the parameters in the joint probability distribution of the random variables are varied. They affect all main features of the theory and the interpretation of statistical models . In this paper a brief review of phase transitions in invariant ensembles is provided, with some comments to the singular values decomposition in complex non-hermitian ensembles.
We have developed a method to determine the transient surface density and transient rate for any given survey, using Monte-Carlo simulations. This method allows us to determine the transient rate as a function of both the flux and the duration of the transients in the whole flux-duration plane rather than one or a few points as currently available methods do. It is applicable to every survey strategy that is monitoring the same part of the sky, regardless the instrument or wavelength of the survey, or the target sources. We have simulated both top-hat and Fast Rise Exponential Decay light curves, highlighting how the shape of the light curve might affect the detectability of transients. Another application for this method is to estimate the number of transients of a given kind that are expected to be detected by a survey, provided that their rate is known.