Miracle-dz/UniFAR-FTUs huggingface dataset:
The velocities of light in modified QED vacua

QED vacua under the influence of external conditions (background fields, finite temperature, boundary conditions) can be considered as dispersive media whose complex behaviour can no longer be described in terms of a single universal vacuum velocity of light c. Beginning in the early 1950's (J.S. Toll), quantum field theoretic investigations have led to considerable insight into the relation between the vacuum structure and the propagation of light. Recent years have witnessed a significant growth of activity in this field of research. After a short overview, two characteristic situations are discussed: the propagation of light in a constant homogeneous magnetic field and in a Casimir vacuum. The latter appears to be particularly interesting because the Casimir vacuum has been found to exhibit modes of the propagation of light with phase and group velocities larger than c in the low frequency domain ω ≪ m where m is the electron mass. The impact of this result on the front velocity of light in a Casimir vacuum is discussed by means of the Kramers‐Kronig relations.
The Evolution of Massive Helium Stars, Including Mass Loss

The evolution of helium stars with initial masses in the range 1.6–120 is studied, including the effects of mass loss by winds. These stars are assumed to form in binary systems when their expanding hydrogenic envelopes are promptly lost just after helium ignition. Significant differences are found with single-star evolution, chiefly because the helium core loses mass during helium burning rather than gaining it from hydrogen shell burning. Consequently, presupernova stars for a given initial mass function have considerably smaller mass when they die and will be easier to explode. Even accounting for this difference, the helium stars with mass loss develop more centrally condensed cores that should explode more easily than their single-star counterparts. The production of low-mass black holes may be diminished. Helium stars with initial masses below 3.2 experience significant radius expansion after helium depletion, reaching blue supergiant proportions. This could trigger additional mass exchange or affect the light curve of the supernova. The most common black hole mass produced in binaries is estimated to be about 9 . A new maximum mass for black holes derived from pulsational pair-instability supernovae is derived, 46 , and a new potential gap at 10–12 is noted. Models pertinent to SN 2014ft are presented, and a library of presupernova models is generated.
Clearing the Smoke: Nebular Spectra of 100+ Type Ia Supernovae Exclude Single Degenerate Progenitors

We place statistical constraints on Type Ia supernova (SN Ia) progenitors using 226 nebular phase spectra of 110 SNe Ia. We find no evidence of stripped companion emission in any of the nebular phase spectra. Upper limits are placed on the amount of mass that could go undetected in each spectrum using recent hydrodynamic simulations. With these null detections, we place an observational $3\sigma$ upper limit on the fraction of SNe Ia that are produced through the classical H-rich non-degenerate companion scenario of $ < 5.6\%$. Additionally, we set a tentative upper limit on He star progenitor scenarios of $< 6.5\%$, although further theoretical modelling is required. As part of our analysis, we also derive a Nebular Phase Phillips Relation, which approximates the brightness of a SN Ia in the nebular phase using the peak magnitude and decline rate parameter $\Delta m_{15} (B)$.
Improved Spray Model for Viscous Annular Sheets in a Swirl Injector

A modified sheet breakup model was applied to a thin, viscous liquid film generated by a swirl injector similar to that installed in a liquid propellant rocket engine combustor. The sheet breakup model consists of three steps: determination of the swirl injector characteristics for the prediction of initial sheet conditions at the injector exit as input, linear stability analysis for primary sheet breakup, and the Taylor analogy breakup model for final drop formation. Under atmospheric pressure, the liquid sheet breakup occurs under a long-wave regime, sometimes according to simple theoretical analysis. But in high ambient pressure conditions, like a liquid propellant rocket engine combustor, the sheet breakup regime changes from a long wave to a short-wave regime due to a high gas Weber number (We 2 > 27/16), although the same injector was used. The sheet breakup model was, therefore, modified to be applicable to both long- and short-wave regimes and validated by the comparison of breakup length and Sauter mean diameter to experimental results. In both experimental and computational results, the spray cone angle and breakup length decreased as the ambient pressure increased, even though the pressure difference of the injector was constant. Local Sauter mean diameters, predicted by computation, were smaller at high ambient pressures. The comparative results show that the computational model is able to accurately predict sheet breakup length, spray cone angle, local Sauter mean diameter, and overall spray shape. Therefore, the model can be used as a design tool, ahead of analyzing spray characteristics of an injector in both atmospheric and high ambient pressure conditions.
Inverse problem for Hawking radiation

In this work we study the inverse problem related to the emission of Hawking radiation. We first show how the knowledge of greybody factors of different angular contributions $l$ can be used to constrain the width of the corresponding black hole perturbation potentials. Afterwards we provide a framework to recover the greybody factors from the actual energy emission spectrum, which has to be treated as sum over all multipole numbers. The underlying method for the reconstruction of the potential widths is based on the inversion of the Gamow formula, a parabolic expansion and the Poschl-Teller potential. We define a `normalized' energy emission spectrum that turns out to be very beneficial for the numerical fitting process, as well as for an improved qualitative understanding of how much information of the black hole potentials are actually imprinted in the spectrum. The connection to recent studies on the inverse problem using the quasi-normal spectra of ultra compact stars and exotic compact objects is discussed as well. In the appendix we show that the spectrum can be approximated surprisingly well and simply with a parabolic expansion of the peak of the classical black hole scattering potentials.
Late Bloomer Galaxies: Growing Up in Cosmic Autumn

Late bloomers (LBs) are massive ( ) galaxies at z < 1 that formed the majority of their stars within ∼2 Gyr of the epoch of observation. Our improved methodology for deriving star formation histories (SFHs) of galaxies at redshifts 0.45 < z < 0.75 from the Carnegie-Spitzer-IMACS Survey includes confidence intervals that robustly distinguish LBs from “old” galaxies. We use simulated SFHs to test for “false positives” and contamination from old galaxies to demonstrate that the late-bloomer population is not an artifact of our template modeling technique. We show that LBs account for ∼20% of z ∼ 0.6 galaxies with masses of the modern Milky Way, with a moderate dependence on mass. We take advantage of a 1% overlap of our sample with HST (CANDELS) imaging to construct a “gold standard” catalog of 74 galaxies with high-confidence SFHs, SEDs, basic data, and HST images to facilitate comparison with future studies by others. This small subset suggests that galaxies with both old and young SFHs cover the full range of morphology and environment (excluding rich groups or clusters), albeit with a mild but suggestive correlation with the local environment. We begin the investigation of whether LBs of sufficient mass and frequency are produced in current-generation ΛCDM-based semianalytic models of galaxy formation. In terms of halo growth, we find a late-assembling halo fraction within a factor of two of our late bloomer fraction. However, sufficiently delaying star formation in such halos may be a challenge for the baryon component of such models.
A Deep Learning Approach to Galaxy Cluster X-Ray Masses

We present a machine-learning (ML) approach for estimating galaxy cluster masses from Chandra mock images. We utilize a Convolutional Neural Network (CNN), a deep ML tool commonly used in image recognition tasks. The CNN is trained and tested on our sample of 7896 Chandra X-ray mock observations, which are based on 329 massive clusters from the simulation. Our CNN learns from a low resolution spatial distribution of photon counts and does not use spectral information. Despite our simplifying assumption to neglect spectral information, the resulting mass values estimated by the CNN exhibit small bias in comparison to the true masses of the simulated clusters (−0.02 dex) and reproduce the cluster masses with low intrinsic scatter, 8% in our best fold and 12% averaging over all. In contrast, a more standard core-excised luminosity method achieves 15%–18% scatter. We interpret the results with an approach inspired by Google DeepDream and find that the CNN ignores the central regions of clusters, which are known to have high scatter with mass.
Submillimeter spatial oscillations of Newton’s constant: Theoretical models and laboratory tests

We investigate the viability of sub-millimeter wavelength oscillating deviations from the Newtonian potential at both the theoretical and the experimental/observational level. At the theoretical level such deviations are generic predictions in a wide range of extensions of General Relativity (GR) including $f(R)$ theories, massive Brans-Dicke theories, compactified extra dimension models and nonlocal extensions of GR. However, the range of parameters associated with such oscillating deviations is usually connected with instabilities. An exception emerges in nonlocal gravity theories where oscillating deviations from Newtonian potential occur naturally on sub-millimeter scales without instabilities. As an example of a model with unstable Newtonian oscillations we review an $f(R)$ expansion around General Relativity of the form $f(R)=R+\frac{1}{6 m^2} R^2$ with $m^2<0$ pointing out possible stabilization mechanisms. As an example of a model with stable Newtonian oscillations we discuss nonlocal gravity theories. If such oscillations are realized in Nature on sub-millimeter scales, a signature is expected in torsion balance experiments testing Newton's law. We search for such a signature in the torsion balance data of the Washington experiment (combined torque residuals) testing Newton's law at sub-millimeter scales. We show that an oscillating residual ansatz with spatial wavelength $\lambda \simeq 0.1mm$ provides a better fit to the data compared to the residual Newtonian constant ansatz by $\Delta \chi^2 = -15$. Similar improved fits, also occur in about $10\%$ of Monte Carlo realizations of Newtonian data. Thus, the significance level of this improved fit is at a level of not more than $2\sigma$. The energy scale corresponding to this best fit wavelength is identical to the dark energy length scale $\lambda_{de} \equiv\sqrt[4]{\hbar c/\rho_{ de}}\approx 0.1mm$.
Radio spectral ageing in a random magnetic field

I study the ageing of radio synchrotron emission from relativistic electrons in a random magnetic field. There is a range of break frequencies corresponding to the range in field strength, so that the sharp break in the spectrum given by the Jaffe-Perola model is not always seen, and the spectra can be very similar to that of the Kardashev-Pacholczyk model. This explains the good fit of the Kardashev-Pacholczyk model to observations, even though the Jaffe-Perola model is more physically reasonable. The lack of an exponential break in the spectrum does not mean that pitch angle scattering does not occur. In the presence of inverse Compton losses, the spectral shape is strongly dependent on rms field strength, allowing equipartition estimates to be checked
Ab initio modeling of open systems: Charge transfer, electron conduction, and molecular switching of a C 60 device

We present an ab initio analysis of electron conduction through a ${\mathrm{C}}_{60}$ molecular device. Charge transfer from the device electrodes to the molecular region is found to play a crucial role in aligning the lowest unoccupied molecular orbital of the ${\mathrm{C}}_{60}$ to the Fermi level of the electrodes. This alignment induces a substantial device conductance of $\ensuremath{\sim}2.2\ifmmode\times\else\texttimes\fi{}{(2e}^{2}/h). $ A gate potential can inhibit charge transfer, and introduce a conductance gap near ${E}_{F},$ changing the current-voltage characteristics from metallic to semiconducting, thereby producing a field-effect molecular current switch.
A Close Look at the State Transitions of Galactic Black Hole Transients during Outburst Decay

We characterize the evolution of spectral and temporal properties of several Galactic black hole transients during outburst decay using the data from well-sampled Rossi X-Ray Timing Explorer Proportional Counter Array observations close to the transition to the low/hard state. We find several global patterns of evolution for spectral and temporal parameters before, during, and after the transition. We show that the changes in temporal properties (sudden increase or decrease in the rms amplitude of variability) are much sharper than the changes in the spectral properties, and it is much easier to identify a state transition with the temporal properties. The spectral index shows a drop 3-5 days before the transition for some of our sources. The ratio of the power-law flux to the total flux in the 3-25 keV band increases close to the transition, which may mean that the system must be dominated by the coronal emission for the transition to occur. We also show that the power-law flux shows a sharp change along with the temporal properties during the transitions, which may indicate a threshold transition volume for the corona. The evolution of the spectral and temporal properties after the transition is consistent with the idea that the inner accretion disk moves away from the black hole. Based on the evolution of spectral and temporal parameters and changes during the transitions, we discuss possible scenarios of how the transition is happening.
Low-redshift quasars in the SDSS Stripe 82: associated companion galaxies and signature of star formation

We present optical spectroscopy of the close companions of 22 low redshift (z<0.5) quasars (QSO) selected from a larger sample of QSO in the SDSS Stripe82 region for which both the host galaxy and the large scale environments have been investigated in our previous work. The new observations extend the number of QSO studied in our previous paper on close companion galaxies of 12 quasars. Our analysis here covers all 34 quasars from both this work and the previously published paper. We find that half of them (15 QSO; $\sim$44%) have at least one associated galaxy. Many (12 galaxies; $\sim$67%) of the associated companions exhibit [OII] 3727 A emission line as signature of recent star formation. The star formation rate (SFR) of these galaxies is modest (median SFR $\sim$ 4.3 M$_{\odot}$ yr$^{-1}$). For 8 QSO we are also able to detect the starlight of the host galaxy from which 3 have a typical spectrum of a post-starburst galaxy. Our results suggest that quasars do not have a strong influence on the star formation of their companion galaxies.
Absorption-Line Study of Halo Gas in NGC 3067 toward the Background Quasar 3C 232

We present new H I 21 cm absorption data and ultraviolet spectroscopy from Hubble Space Telescope/Space Telescope Imaging Spectrograph of the QSO/galaxy pair 3C 232/NGC 3067. The QSO sight line lies near the minor axis and 1. ′8 (11 h kpc) above the plane of NGC 3067, a nearby luminous (cz = 1465 ± 5 km s-1, L = 0.5 L*) starburst galaxy with a moderate star formation rate of 1.4 M☉ yr-1. The UV spectra show that the Si IV and C IV doublets have the same three velocity components at cz = 1369, 1417, and 1530 km s-1 found in Ca II H and K, Na I D, Mg I, Mg II, and Fe II, implying that the low- and high-ionization gas are both found in three distinct absorbing clouds (only the strongest component at 1420 km s-1 is detected in H I 21 cm). The new Lyα observation allows the first measurements of the spin and kinetic temperatures of halo gas: Ts = 435 ± 140 K and Tk/Ts ≈ 1. However, while a standard photoionization model can explain the low ions, the C IV and Si IV are explained more easily as collisionally ionized boundary layers of the photoionized clouds. Because of their small inferred space velocity offsets (Δv = -260, -130, and +170 km s-1) relative to the nucleus of NGC 3067 and the spatial coincidence of low- and high-ionization gas, we propose that these absorbers are analogous to Galactic high-velocity clouds (HVCs). A comparison of the NGC 3067 clouds and Galactic HVCs finds similar H I column densities, kinematics, metallicities, spin temperatures, and inferred sizes. We find no compelling evidence that any halo gas along this sight line is escaping the gravitational potential of NGC 3067, despite its modest starburst.
The Changing-look Quasar Mrk 590 Is Awakening

Mrk 590 was originally classified as a Seyfert 1 galaxy, but then it underwent dramatic changes: the nuclear luminosity dropped by over two orders of magnitude and the broad emission lines all but disappeared from the optical spectrum. Here we present follow-up observations to the original discovery and characterization of this “changing-look” active galactic nucleus (AGN). The new Chandra and Hubble Space Telescope observations from 2014 show that Mrk 590 is awakening, changing its appearance again. While the source continues to be in a low state, its soft excess has re-emerged, though not to the previous level. The UV continuum is brighter by more than a factor of two and the broad Mg ii emission line is present, indicating that the ionizing continuum is also brightening. These observations suggest that the soft excess is not due to reprocessed hard X-ray emission. Instead, it is connected to the UV continuum through warm Comptonization. Variability of the Fe Kα emission lines suggests that the reprocessing region is within ∼10 lt-yr or 3 pc of the central source. The change in AGN type is neither due to obscuration nor due to one-way evolution from Type 1 to Type 2, as suggested in the literature, but may be related to episodic accretion events.
Dynamically Encircling Exceptional Points: 
In situ
 Control of Encircling Loops and the Role of the Starting Point

The most intriguing properties of non-Hermitian systems are found near the exceptional points (EPs) at which the Hamiltonian matrix becomes defective. Due to the complex topological structure of the energy Riemann surfaces close to an EP and the breakdown of the adiabatic theorem due to non-Hermiticity, the state evolution in non-Hermitian systems is much more complex than that in Hermitian systems. For example, recent experimental work [Doppler et al. Nature 537, 76 (2016)] demonstrated that dynamically encircling an EP can lead to chiral behaviors, i.e., encircling an EP in different directions results in different output states. Here, we propose a coupled ferromagnetic waveguide system that carries two EPs and design an experimental setup in which the trajectory of state evolution can be controlled in situ using a tunable external field, allowing us to dynamically encircle zero, one or even two EPs experimentally. The tunability allows us to control the trajectory of encircling in the parameter space, including the size of the encircling loop and the starting/end point. We discovered that whether or not the dynamics is chiral actually depends on the starting point of the loop. In particular, dynamically encircling an EP with a starting point in the parity-time-broken phase results in non-chiral behaviors such that the output state is the same no matter which direction the encircling takes. The proposed system is a useful platform to explore the topology of energy surfaces and the dynamics of state evolution in non-Hermitian systems and will likely find applications in mode switching controlled with external parameters.
Curvature and isocurvature perturbations in a three-fluid model of curvaton decay

We study the evolution of the cosmological perturbations after inflation in curvaton models where the non-relativistic curvaton decays into both radiation and a cold dark matter component. We calculate the primordial curvature and correlated isocurvature perturbations inherited by the radiation and cold dark matter after the curvaton has decayed. We give the transfer coefficient in terms of the initial curvaton density relative to the curvaton decay rate.
The Ks-band luminosity and stellar mass functions of galaxies in z ∼ 1 clusters

We present the near-infrared (K s -band) luminosity function of galaxies in two z ∼ 1 cluster candidates, 3C 336 and Q1335+28. A third cluster, 3C 289, was observed but found to be contaminated by a foreground system. Our wide-field imaging data reach to K s = 20.5 (5σ), corresponding to ∼ M* + 2.7 with respect to passive evolution. The near-infrared luminosity traces the stellar mass of a galaxy due to its small sensitivity to the recent star formation history. Thus the luminosity function can be transformed to the stellar mass function of galaxies using the J - K s colours with only a small correction (factor? 2) for the effects of ongoing star formation. The derived stellar mass function spans a wide range in mass from ∼3 x 10 1 1 M O . down to ∼6 x 10 9 M O . (set by the magnitude limit). The form of the mass function is very similar to lower-redshift counterparts such as that from 2MASS/LCRS clusters (given by Balogh et al.) and the z = 0.31 clusters (given by Barger et al.). This indicates little evolution of galaxy masses from z = 1 to the present day. Combined with colour data suggesting that star formation is completed early (z » 1) in the cluster core, it seems that the galaxy formation processes (both star formation and mass assembly) are strongly accelerated in dense environments and have been largely completed by z = 1. We investigate whether the epoch of mass assembly of massive cluster galaxies is earlier than that predicted by the semi-analytic hierarchical galaxy formation models. These models predict the increase of characteristic mass by more than a factor of ∼3 between z = 1 and the present day. This seems incompatible with our data.
Star Formation and Chemical Evolution in Damped LY alpha Clouds

Using the redshift evolution of the neutral hydrogen density, as inferred from observations of damped Ly$\alpha$ clouds, we calculate the evolution of star formation rates and elemental abundances in the universe. For most observables our calculations are in rough agreement with previous results based on the instantaneous re-cycling approximation (IRA). However, for the key metallicity tracer Zn, we find a better match to the observed abundance at high redshift than that given by the constant-yield IRA model. We investigate whether the redshift evolution of deuterium, depressions in the diffuse extragalactic gamma-ray background, and measurement of the MeV neutrino background may help determine if observational bias due to dust obscuration is important. We also indicate how the importance of dust on the calculations can be significantly reduced if correlations of the HI column density with metallicity are present. The possibilities for measuring $q_o$ with observations of elemental abundances in damped Ly$\alpha$ systems are discussed.