Miracle-dz/UniFAR-FTUs huggingface dataset:
Local projection stabilized finite element modeling of viscoelastic two-phase flows

A three-field local projection stabilized finite element method is developed for computations of a 3D-axisymmetric buoyancy driven bubble rising in a liquid column in which either the bubble or the liquid column can be viscoelastic. The two-phase flow is described by the time-dependent incompressible Navier--Stokes equations, whereas the viscoelasticity is modeled by the Giesekus constitutive equation in a time-dependent domain. The arbitrary Lagrangian Eulerian~(ALE) formulation with finite elements is used to solve the governing equations in the time-dependent domain. The interface-resolved moving meshes in ALE allows to incorporate the interfacial tension force and jumps in the material parameters accurately. An one-level Local Projection Stabilization~(LPS), which is based on an enriched approximation space and a discontinuous projection space, where both spaces are defined on a same mesh is used to stabilize the model equations. The stabilized numerical scheme allows us to use equal order interpolation spaces for the velocity and the viscoelastic stress, whereas inf-sup stable finite elements are used for the velocity and the pressure. A comprehensive numerical investigation is performed for a Newtonian bubble rising in a viscoelastic fluid and a viscoelastic bubble rising in a Newtonian fluid. The influence of the viscosity ratio, Newtonian solvent ratio, Giesekus mobility factor and the Eotvos number on the bubble dynamics are analyzed. The numerical study shows that a Newtonian bubble rising in a viscoelastic fluid experiences an extended trailing edge with a cusp-like shape and also exhibits the negative wake phenomena. However, a viscoelastic bubble rising in a Newtonian fluid develops an indentation around the rear stagnation point with a dimpled shape.
Applicability of DFT + U to U metal and U-Zr alloy

In the Letter [J. Nucl. Mater. 444, 356 (2014)] and Comment [Phys Rev B 90, 157101 (2014)], Soderlind et al. argue that 1) DFT based on GGA already models U metal and U-Zr alloy accurately, and 2) DFT + U models them worse than DFT according to results they calculate or select from our recent study [Phys. Rev. B 88, 235128 (2013)]. Here we demonstrate in response to 1) that previously neglected and more recent experimental data indicate that DFT, even when implemented in all-electron methods, does not model the bulk modulus and elastic constants of {\alpha}U very accurately. Furthermore, Soderlind et al.'s claim that deficiency exists in our PAW calculation is unfounded and hence our results, including those that show DFT results compare unfavorably with experimental/computational references, are valid. We also demonstrate in response to 2) that Soderlind et al.'s arguments are unsound for three reasons. First, they focus on just the BCC phases {\gamma}U and {\gamma}(U,Zr)--which at the ab initio modeling temperature of 0 K are unstable and hence difficult to model and benchmar--as primary subjects of examination; however it is results for the stable phases mostly neglected by Soderlind et al. that are the primary evidence of our argument. Second, they make unfounded generalization of DFT + U results at selected U eff values to argue that DFT + U in general gives wrong or unsatisfactory results. Third, some key points in Soderlind et al.'s criticisms of DFT + U are not well supported, including the claims that for {\gamma}(U,Zr) DFT + U at Ueff = 1.24 eV gives positive deviations from linear dependence of composition that are unprecedentedly large and partially negative enthalpies of mixing that are inconsistent with the existence of miscibility gap in the experimental phase diagram. We therefore maintain our conclusion that DFT + U can be of value for modeling U and U-Zr.
The critical accretion luminosity for magnetized neutron stars

The accretion flow around X-ray pulsars with a strong magnetic field is funnelled by the field to relatively small regions close to the magnetic poles of the neutron star (NS), the hotspots. During strong outbursts regularly observed from some X-ray pulsars, the X-ray luminosity can be so high, that the emerging radiation is able to stop the accreting matter above the surface via radiation-dominated shock, and the accretion column begins to rise. This border luminosity is usually called the "critical luminosity". Here we calculate the critical luminosity as a function of the NS magnetic field strength $B$ using exact Compton scattering cross section in strong magnetic field. Influence of the resonant scattering and photon polarization is taken into account for the first time. We show that the critical luminosity is not a monotonic function of the B-field. It reaches a minimum of a few 10^{36} erg s^{-1} when the cyclotron energy is about 10 keV and a considerable amount of photons from a hotspot have energy close to the cyclotron resonance. For small B, this luminosity is about 10^{37} erg s^{-1}, nearly independent of the parameters. It grows for the B-field in excess of 10^{12} G because of the drop in the effective cross-section of interaction below the cyclotron energy. We investigate how different types of the accretion flow and geometries of the accretion channel affect the results and demonstrate that the general behaviour of the critical luminosity on B-field is very robust. The obtained results are shown to be in a good agreement with the available observational data and provide a necessary ground for the interpretation of upcoming high quality data from the currently operating and planned X-ray telescopes.
DOUBLE SPECIAL RELATIVITY WITH A MINIMUM SPEED AND THE UNCERTAINTY PRINCIPLE

The present work aims to search for an implementation of a new symmetry in the spacetime by introducing the idea of an invariant minimum speed scale (V). Such a lowest limit V, being unattainable by the particles, represents a fundamental and preferred reference frame connected to a universal background field (a vacuum energy) that breaks Lorentz symmetry. So there emerges a new principle of symmetry in the spacetime at the subatomic level for very low energies close to the background frame (v ≈ V), providing a fundamental understanding for the uncertainty principle, i.e. the uncertainty relations should emerge from the spacetime with an invariant minimum speed.
Non-gaussianity in axion N-flation models: detailed predictions and mass spectra

We have recently shown that multi-field axion N-flation can lead to observable non-gaussianity in much of its parameter range, with the assisted inflation mechanism ensuring that the density perturbations are sufficiently close to scale invariance. In this paper we extend our analysis in several directions. In the case of equal-mass axions, we compute the probability distributions of observables and their correlations across the parameter space. We examine the case of unequal masses, and show that the mass spectrum must be very densely packed if the model is to remain in agreement with observations. The model makes specific testable predictions for all major perturbative observables, namely the spectral index, tensor-to-scalar ratio, bispectrum, and trispectrum.
Influence of convex spherical device on the local field distribution in the microwave reaction cavity

Uneven energy distribution and “hotspot” phenomenon are bottlenecks restricting the development of the microwave heating industry. The formation of high-intensity electric field aggregation areas can be effectively repressed by optimizing the reaction cavity structures. With a box-type microwave reaction cavity as the study object and a built-in convex spherical as the induction device, the influences of the structural parameters of different devices on the microwave local field distribution were analytically explored through the simulation technology, and a “hotspot” early warning method was proposed. This study provides a reference for inhibiting the “hotspot” phenomenon on microwave fields and optimally designing microwave reactors.
The chiral transition and $U(1)_A$ symmetry restoration from lattice QCD using Domain Wall Fermions

We present results on both the restoration of the spontaneously broken chiralsymmetry and the effective restoration of the anomalously broken U(1)_Asymmetry in finite temperature QCD at zero chemical potential using latticeQCD. We employ domain wall fermions on lattices with fixed temporal extentN_\tau = 8 and spatial extent N_\sigma = 16 in a temperature range of T = 139 -195 MeV, corresponding to lattice spacings of a \approx 0.12 - 0.18 fm. Inthese calculations, we include two degenerate light quarks and a strange quarkat fixed pion mass m_\pi = 200 MeV. The strange quark mass is set near itsphysical value. We also present results from a second set of finite temperaturegauge configurations at the same volume and temporal extent with slightlyheavier pion mass. To study chiral symmetry restoration, we calculate thechiral condensate, the disconnected chiral susceptibility, and susceptibilitiesin several meson channels of different quantum numbers. To study U(1)_Arestoration, we calculate spatial correlators in the scalar and pseudo-scalarchannels, as well as the corresponding susceptibilities. Furthermore, we alsoshow results for the eigenvalue spectrum of the Dirac operator as a function oftemperature, which can be connected to both U(1)_A and chiral symmetryrestoration via Banks-Casher relations.
Step-emulsification in nanofluidic device

In this paper we present a comprehensive study of the step-emulsification process for high-throughput production of (sub-)$\mu$m-size monodisperse droplets. The microfluidic device combines a Hele-Shaw nanofluidic cell with a step-like outlet to a deep and wide reservoir. The proposed theory based on Hele-Shaw hydrodynamics provides the quasi-static shape of the free boundary between the disperse liquid phase engulfed by the co-flowing continuous phase prior to transition to oscillatory step-emulsification at low enough capillary number. At the transition the proposed theory anticipates a simple condition for critical capillary number as a function of the Hele-Shaw cell geometry. The transition threshold is in excellent agreement with experimental data. A simple closed-form expression for the size of the droplets generated in step-emulsification regime derived using simple geometric arguments also shows a very good agreement with the experimental results.
THE ORIGIN OF METALS IN THE CIRCUMGALACTIC MEDIUM OF MASSIVE GALAXIES AT z = 3

We present a detailed study of the metal-enriched circumgalactic medium (CGM) of a massive galaxy at z = 3 using results from “ErisMC,” a new cosmological hydrodynamic “zoom-in” simulation of a disk galaxy with mass comparable to the Milky Way. The reference run adopts a blast wave scheme for supernova feedback that generates galactic outflows without explicit wind particles, a star formation recipe based on a high gas density threshold and high-temperature metal cooling. ErisMC's main progenitor at z = 3 resembles a “Lyman break” galaxy of total mass Mvir = 2.4 × 1011 M☉, virial radius Rvir = 48 kpc, and star formation rate 18 M☉ yr−1, and its metal-enriched CGM extends as far as 200 (physical) kpc from its center. Approximately 41%, 9%, and 50% of all gas-phase metals at z = 3 are locked in a hot (T > 3 × 105 K), warm (3 × 105 K > T > 3 × 104 K), and cold (T < 3 × 104 K) medium, respectively. We identify three sources of heavy elements: (1) the main host, responsible for 60% of all the metals found within 3 Rvir; (2) its satellite progenitors, which shed their metals before and during infall, and are responsible for 28% of all the metals within 3 Rvir, and for only 5% of those beyond 3 Rvir; and (3) nearby dwarfs, which give origin to 12% of all the metals within 3 Rvir and 95% of those beyond 3 Rvir. Late (z < 5) galactic “superwinds”—the result of recent star formation in ErisMC—account for only 9% of all the metals observed beyond 2 Rvir, the bulk having been released at redshifts 5 ≲ z ≲ 8 by early star formation and outflows. In the CGM, lower overdensities are typically enriched by “older,” colder metals. Heavy elements are accreted onto ErisMC along filaments via low-metallicity cold inflows and are ejected hot via galactic outflows at a few hundred km s−1. The outflow mass-loading factor is of order unity for the main halo, but can exceed a value of 10 for nearby dwarfs. We stress that our “zoom-in” simulation focuses on the CGM of a single massive system and cannot describe the enrichment history of the intergalactic medium as a whole by a population of galaxies with different masses and star formation histories.
ON THE ROLE OF PSEUDODISK WARPING AND RECONNECTION IN PROTOSTELLAR DISK FORMATION IN TURBULENT MAGNETIZED CORES

The formation of rotationally supported protostellar disks is suppressed in ideal MHD in non-turbulent cores with aligned magnetic fields and rotation axes. A promising way to resolve this so-called “magnetic braking catastrophe” is through turbulence. The reason for the turbulence-enabled disk formation is usually attributed to the turbulence-induced magnetic reconnection, which is thought to reduce the magnetic flux accumulated in the disk-forming region. We advance an alternative interpretation, based on magnetic decoupling-triggered reconnection of severely pinched field lines close to the central protostar and turbulence-induced warping of the pseudodisk of Galli and Shu. Such reconnection weakens the central split magnetic monopole that lies at the heart of the magnetic braking catastrophe under flux freezing. We show, through idealized numerical experiments, that the pseudodisk can be strongly warped, but not completely destroyed, by a subsonic or sonic turbulence. The warping decreases the rates of angular momentum removal from the pseudodisk by both magnetic torque and outflow, making it easier to form a rotationally supported disk. More importantly, the warping of the pseudodisk out of the disk-forming, equatorial plane greatly reduces the amount of magnetic flux threading the circumstellar, disk-forming region, further promoting disk formation. The beneficial effects of pseudodisk warping can also be achieved by a misalignment between the magnetic field and rotation axis. These two mechanisms of disk formation, enabled by turbulence and field-rotation misalignment respectively, are thus unified. We find that the disks formed in turbulent magnetized cores are rather thick and significantly magnetized. Implications of these findings, particularly for the thick young disk inferred in L1527, are briefly discussed.
Observational constraints to boxy/peanut bulge formation time

Boxy/peanut bulges are considered to be part of the same stellar structure as bars and both could be linked through the buckling instability. The Milky Way is our closest example. The goal of this Letter is to determine if the mass assembly of the different components leaves an imprint in their stellar populations allowing the estimation the time of bar formation and its evolution. To this aim, we use integral field spectroscopy to derive the stellar age distributions, SADs, along the bar and disc of NGC 6032. The analysis clearly shows different SADs for the different bar areas. There is an underlying old (≥12 Gyr) stellar population for the whole galaxy. The bulge shows star formation happening at all times. The inner bar structure shows stars of ages older than 6 Gyr with a deficit of younger populations. The outer bar region presents an SAD similar to that of the disc. To interpret our results, we use a generic numerical simulation of a barred galaxy. Thus, we constrain, for the first time, the epoch of bar formation, the buckling instability period and the posterior growth from disc material. We establish that the bar of NGC 6032 is old, formed around 10 Gyr ago while the buckling phase possibly happened around 8 Gyr ago. All these results point towards bars being long-lasting even in the presence of gas.
Unveiling the remarkable photodissociation region of Messier 8

Aims. Messier 8 (M8) is one of the brightest HII regions in the sky. We collected an extensive dataset comprising multiple sub- millimeter spectral lines from neutral and ionized carbon and from CO. Based on this dataset, we aim to understand the morphology of M8 and that of its associated photodissociation region (PDR) and to carry out a quantitative analysis of the physical conditions of these regions such as kinetic temperatures and volume densities. Methods. We used the Stratospheric Observatory For Infrared Astronomy (SOFIA), the Atacama Pathfinder Experiment (APEX) 12 m, and the Institut de Radioastronomie Millimétrique (IRAM) 30 m telescopes to perform a comprehensive imaging survey of the emission from the fine structure lines of [C II] and [C I] and multiple rotational transitions of carbon monoxide (CO) isotopologs within 1.3 × 1.3 pc around the dominant Herschel 36 (Her 36) system, which is composed of at least three massive stars. To further explore the morphology of the region, we compared archival infrared, optical, and radio images of the nebula with our newly obtained fine structure line and CO data, and in particular with the velocity information these data provide. We performed a quantitative analysis, using both LTE and non-LTE methods to determine the abundances of some of the observed species, kinetic temperatures, and volume densities. Results. Bright CO, [C II] and [C I] emission have been found toward the HII region and the PDR in M8. Our analysis places the bulk of the molecular material in the background of the nebulosity illuminated by the bright stellar systems Her 36 and 9 Sagitarii. Since the emission from all observed atomic and molecular tracers peaks at or close to the position of Her 36, we conclude that the star is still physically close to its natal dense cloud core and heats it. A veil of warm gas moves away from Her 36 toward the Sun and its associated dust contributes to the foreground extinction in the region. One of the most prominent star forming regions in M8, the Hourglass Nebula, is particularly bright due to cracks in this veil close to Her 36. We obtain H2 densities ranging from ~104–106 cm–3 and kinetic temperatures of 100–150 K in the bright PDR caused by Her 36 using radiative transfer modeling of various transitions of CO isotopologs.
New Results on the Thermodynamic Properties of the Climate System

AbstractIn this paper the authors exploit two equivalent formulations of the average rate of material entropy production in the climate system to propose an approximate splitting between contributions due to vertical and eminently horizontal processes. This approach is based only on 2D radiative fields at the surface and at the top of atmosphere. Using 2D fields at the top of atmosphere alone, lower bounds to the rate of material entropy production and to the intensity of the Lorenz energy cycle are derived. By introducing a measure of the efficiency of the planetary system with respect to horizontal thermodynamic processes, it is possible to gain insight into a previous intuition on the possibility of defining a baroclinic heat engine extracting work from the meridional heat flux. The approximate formula of the material entropy production is verified and used for studying the global thermodynamic properties of climate models (CMs) included in the Program for Climate Model Diagnosis and Intercomparison (P.
Velocity Anisotropy in Self-gravitating Molecular Clouds. I. Simulation

The complex interplay between turbulence, magnetic fields, and self-gravity leads to the formation of molecular clouds out of the diffuse interstellar medium (ISM). One avenue of studying this interplay is by analyzing statistical features derived from observations, where the interpretation of these features is greatly facilitated by comparisons with numerical simulations. Here we focus on the statistical anisotropy present in synthetic maps of velocity centroid data, which we derive from three-dimensional magnetohydrodynamic simulations of a turbulent, magnetized, self-gravitating patch of ISM. We study how the orientation and magnitude of the velocity anisotropy correlate with the magnetic field and with the structures generated by gravitational collapse. Motivated by recent observational constraints, our simulations focus on the supersonic (sonic Mach number  ≈ 2 – 17 ) but sub- to trans-alfvénic (alfvénic Mach number  A ≈ 0.2 – 1.2 ) turbulence regime, and we consider clouds that are barely to mildly magnetically supercritical (mass-to-flux ratio equal to once or twice the critical value). Additionally we explore the impact of the turbulence driving mechanism (solenoidal or compressive) on the velocity anisotropy. While we confirm previous findings that the velocity anisotropy generally aligns well with the plane-of-sky magnetic field, our inclusion of the effects of self-gravity reveals that in regions of higher column density, the velocity anisotropy may be destroyed or even reoriented to align with the gravitationally formed structures. We provide evidence that this effect is not necessarily due to the increase of  A inside the high-density regions.
The Broad Absorption Line Tidal Disruption Event iPTF15af: Optical and Ultraviolet Evolution

We present multiwavelength observations of the tidal disruption event (TDE) iPTF15af, discovered by the intermediate Palomar Transient Factory survey at redshift z = 0.07897. The optical and ultraviolet (UV) light curves of the transient show a slow decay over 5 months, in agreement with previous optically discovered TDEs. It also has a comparable blackbody peak luminosity of . The inferred temperature from the optical and UV data shows a value of (3–5) × 104 K. The transient is not detected in X-rays up to within the first 5 months after discovery. The optical spectra exhibit two distinct broad emission lines in the He ii region, and at later times also Hα emission. Additionally, emission from [N iii] and [O iii] is detected, likely produced by the Bowen fluorescence effect. UV spectra reveal broad emission and absorption lines associated with high-ionization states of N v, C iv, Si iv, and possibly P v. These features, analogous to those of broad absorption line quasars (BAL QSOs), require an absorber with column densities cm−2. This optically thick gas would also explain the nondetection in soft X-rays. The profile of the absorption lines with the highest column density material at the largest velocity is opposite that of BAL QSOs. We suggest that radiation pressure generated by the TDE flare at early times could have provided the initial acceleration mechanism for this gas. Spectral UV line monitoring of future TDEs could test this proposal.