Miracle-dz/UniFAR-FTUs huggingface dataset:
Effects of growth orientations and epitaxial strains on phase stability of 
HfO2
 thin films

The discovery of ferroelectricity in both pure and doped HfO$_2$-based thin films have revitalized the interest in using ferroelectrics for nanoscale device applications. To take advantage of this silicon-compatible ferroelectric, fundamental questions such as the origin of ferroelectricity and better approach to controlled realization of ferroelectricity at the nanoscale need to be addressed. The emergence of robust polarization in HfO$_2$-based thin films is considered as the cumulative effect of various extrinsic factors such as finite-size effects and surface/interface effects of small grains, compressive stress, dopants, oxygen vacancies, and electric fields. The kinetic effects of phase transitions and their potential impacts on the emergence of ferroelectricity in HfO$_2$ at the nanoscale are not well understood. In this work, we construct the transition paths between different polymorphs of hafnia with density functional theory calculations and variable-cell nudged elastic band technique. We find that the transition barriers depend strongly on the mechanical boundary conditions and the transition from the tetragonal phase to the polar orthorhombic phase is a fast process kinetically under clamping. The effects of growth orientations and epitaxial strains on the relative stability of different phases of HfO$_2$ are investigated. The two orthorhombic phases, polar $Pca2_1$ and non-polar $Pbca$, become thermodynamically stable in (111)-oriented thin films over a wide range of epitaxial strain conditions. This work suggests a potential avenue to better stabilize the ferroelectric phase in HfO$_2$ thin films through substrate orientation engineering.
A gradient expansion for cosmological backreaction

We address the issue of cosmological backreaction from non-linear structure formation by constructing an approximation for the time evolved metric of a dust dominated universe based on a gradient expansion. Our metric begins as a perturbation of a flat Friedmann-Robertson-Walker state described by a nearly scale invariant, Gaussian, power-law distribution, and evolves in time until non-linear structures have formed. After describing and attempting to control for certain complications in the implementation of this approach, this metric then forms a working model of the universe. We numerically calculate the evolution of the average scale factor in this model and hence the backreaction. We argue that, despite its limitations, this model is more realistic than previous models that have confronted the issue of backreaction. We find that the instantaneous effects of backreaction in this model could be as large as ~ 10% of the background. This suggests that a proper understanding of the cumulative effects of backreaction could be crucial for precision cosmology and any future exploration of the dark sector.
Heterotic string field theory with cyclic L∞ structure

We construct a complete heterotic string field theory that includes both the Neveu-Schwarz and Ramond sectors. We give a construction of general string products, which realizes a cyclic L-infinity structure and thus provides with a gauge-invariant action in the homotopy algebraic formulation. Through a map of the string fields, we also give the Wess-Zumino-Witten-like action in the large Hilbert space, and verify its gauge invariance independently.
Biologically Plausible Illusionary Contrast Perception with Spiking Neural Networks

Illusionary visual perception has been long used to shed light on biological vision pathways and mechanisms. In this work, we propose a biologically plausible spiking neural network with which spike events are used for iterative image reconstruction in which illusionary contrast perception, long known to manifest in human vision, is apparent. This parametric implementation allows us to examine this visual phenomenon in a biologically plausible computational framework, which may also account for differences in individual visual perception.
Dark matter response to galaxy assembly history

Aims. It is well known that the presence of baryons affects the dark matter host haloes. Exploring the galaxy assembly history together with the dark matter haloes properties through time can provide a way to measure these effects. Methods. We have studied the properties of four Milky Way mass dark matter haloes from the Aquarius project during their assembly history, between z = 0 − 4. In this work, we used a published SPH run and the dark matter only counterpart as case studies. To asses the robustness of our findings, we compared them with one of the haloes run using a moving-mesh technique and different sub-grid scheme. Results. Our results show that the cosmic evolution of the dark matter halo profiles depends on the assembly history of the baryons. We find that the dark matter profiles do not significantly change with time, hence they become stable, when the fraction of baryons accumulated in the central regions reaches 80 per cent of its present mass within the virial radius. Furthermore, the mass accretion history shows that the haloes that assembled earlier are those that contain a larger amount of baryonic mass aforetime, which in turn allows the dark matter halo profiles to reach a stable configuration earlier. For the SPH haloes, we find that the specific angular momentum of the dark matter particles within the five per cent of the virial radius at z = 0, remains approximately constant from the time at which 60 per cent of the stellar mass is gathered. We have explored different theoretical and empirical models for the contraction of the haloes through redshift. A model to better describe the contraction of the haloes through redshift evolution must depend on the stellar mass content in the inner regions.
A volume-limited survey of mCP stars within 100 pc – I. Fundamental parameters and chemical abundances

We present the first results of a volume-limited survey of main sequence (MS) magnetic chemically peculiar (mCP) stars. The sample consists of all identified intermediate-mass MS stars (mCP and non-mCP) within a heliocentric distance of $100\,{\rm pc}$ as determined using Hipparcos parallaxes. The two populations are compared in order to determine the unique properties that allow a small fraction of MS stars with masses $\gtrsim1.4\,M_\odot$ to host strong, large scale magnetic fields. A total of 52 confirmed mCP stars are identified using published magnetic, spectroscopic, and photometric observations along with archived and newly obtained spectropolarimetric (Stokes $V$) observations. We derive the fundamental parameters (effective temperatures, luminosities, masses, and evolutionary states) of the mCP and non-mCP populations using homogeneous analyses. A detailed analysis of the mCP stars is performed using the {\sc llmodels} code, which allows observed spectral energy distributions to be modeled while incorporating chemical peculiarities and magnetic fields. The surface gravities and mean chemical abundances are derived by modelling averaged spectra using the {\sc gssp} and {\sc zeeman} spectral synthesis codes. Masses and stellar ages are derived using modern, densely calculated evolutionary model grids. We confirm a number of previously reported evolutionary properties associated with mCP stars including a conspicuously high incidence of middle-aged MS stars with respect to the non-mCP subsample; the incidence of mCP stars is found to sharply increase with mass from $0.3$~per~cent at $1.5\,M_\odot$ to $\approx11$~per~cent at $3.8\,M_\odot$. Finally, we identify clear trends in the mean photospheric chemical abundances with stellar age.
From radio-quiet to radio-silent: low-luminosity Seyfert radio cores

A strong effort has been devoted to understand the physical origin of radio emission from low-luminosity AGN (LLAGN), but a comprehensive picture is still missing. We used high-resolution ($\le$1 arcsec), multi-frequency (1.5, 5.5, 9 and 14 GHz) NSF's Karl G. Jansky Very Large Array (VLA) observations to characterise the state of the nuclear region of ten Seyfert nuclei, which are the faintest members of a complete, distance-limited sample of 28 sources. With the sensitivity and resolution guaranteed by the VLA-A configuration, we measured radio emission for six sources (NGC3185, NGC3941, NGC4477, NGC4639, NGC4698 and NGC4725), while for the remaining four (NGC0676, NGC1058, NGC2685 and NGC3486) we put upper limits at tens uJy/beam level, below the previous 0.12 mJy/beam level of Ho&Ulvestad (2001), corresponding to luminosities down to L$\le10^19$ W/Hz at 1.5 GHz for the highest RMS observation. Two sources, NGC4639 and NGC4698, exhibit spectral slopes compatible with inverted spectra ($\alpha\le$0, $S_\nu\,\propto\,\nu^-\alpha$), hint for radio emission from an optically-thick core, while NGC4477 exhibits a steep (+0.52$\pm$0.09) slope. The detected sources are mainly compact on scales $\le$ arcseconds, predominantly unresolved, except NGC3185 and NGC3941, in which the resolved radio emission could be associated to star-formation processes. A significant X-ray - radio luminosities correlation is extended down to very low luminosities, with slope consistent with inefficient accretion, expected at such low Eddington ratios. Such sources will be one of the dominant Square Kilometre Array (SKA) population, allowing a deeper understanding of the physics underlying such faint AGN.
ALL-SKY INTERFEROMETRY WITH SPHERICAL HARMONIC TRANSIT TELESCOPES

In this paper, we describe the spherical harmonic transit telescope through the use of a novel formalism for the analysis of transit radio telescopes. This all-sky approach bypasses the curved-sky complications of traditional interferometry and so is particularly well-suited to the analysis of wide-field radio interferometers. It enables compact and computationally efficient representations of the data and its statistics, which allow new ways of approaching important problems like map-making and foreground removal. In particular, we show how it enables the use of the Karhunen-Loève transform as a highly effective foreground filter, suppressing realistic foreground residuals for our fiducial example by at least a factor 20 below the 21 cm signal, even in highly contaminated regions of the sky. This is despite the presence of the mode-mixing inherent in real-world instruments with frequency-dependent beams. We show, using Fisher forecasting, that foreground cleaning has little effect on power spectrum constraints compared to hypothetical foreground-free measurements. Beyond providing a natural real-world data analysis framework for 21 cm telescopes now under construction and future experiments, this formalism allows accurate power spectrum forecasts to be made that include the interplay of design constraints and realistic experimental systematics with 21st century 21 cm science.
URBAN TRANSPORT INFRASTRUCTURE FOR PEOPLE WITH DISABILITIES IN THE CITY OF TSHWANE, SOUTH AFRICA: AN OBSERVATION AUDIT

People with disabilities often find it difficult to access public transport. The purpose of this study was to identify issues with urban transport infrastructure in the City of Tshwane that contribute to inaccessible transportation. An observational checklist was prepared to collect data, and the checklist was based on guidelines and best practices for universally accessible transport. The infrastructure elements considered in this study were pavements, street crossings, street furniture, bus stops, bus station, taxi ranks and train stations. To a large extent, the design of transport infrastructure in the City of Tshwane does not comply with universal design principles and, in areas where there was compliance, there was a distinct lack of consistency. The study results revealed that the urban transport infrastructure in the City of Tshwane is not designed to cater to the needs of people with disability. The results also revealed that existing transport infrastructure lacks maintenance. It is recommended that the city train city planners and built environment professionals on disability building regulations. City planners and built environment professionals should be conscious of the needs of different groups of people when planning and designing city infrastructure.
Energy-momentum tensor of a Casimir apparatus in a weak gravitational field: Scalar case

Recent work in the literature had evaluated the energy-momentum tensor of a Casimir apparatus in a weak gravitational field, for an electromagnetic field subject to perfect conductor boundary conditions on parallel plates. The Casimir apparatus was then predicted to experience a tiny push in the upward direction, and the regularized energy-momentum tensor was evaluated to first order in the gravitational acceleration. This analysis made it desirable to assess what happens in a simpler case. For this purpose, the present paper studies a free, real massless scalar field subject to homogeneous Dirichlet conditions on the parallel plates. Working again to first order in the constant gravity acceleration, the resulting regularized and renormalized energy-momentum tensor is found to be covariantly conserved, while the trace anomaly vanishes if the massless scalar field is conformally coupled to gravity. Conformal coupling also ensures a finite Casimir energy and finite values of the pressure upon parallel plates. (Less)
The Li–age correlation: the Sun is unusually Li deficient for its age

The present work aims to examine in detail the depletion of lithium in solar twins to better constrain stellar evolution models and investigate its possible connection with exoplanets. We employ spectral synthesis in the region of the asymmetric 6707.75 \AA Li I line for a sample of 77 stars plus the Sun. As in previous works based on a smaller sample of solar twins, we find a strong correlation between Li depletion and stellar age. In addition, for the first time we show that the Sun has the lowest Li abundance in comparison with solar twins at similar age (4.6 $\pm$ 0.5 Gyr). We compare the lithium content with the condensation temperature slope for a sub-sample of the best solar twins and determine that the most lithium depleted stars also have fewer refractory elements. We speculate whether the low lithium content in the Sun might be related to the particular configuration of our Solar system.
A CENSUS OF LARGE-SCALE (≥10 PC), VELOCITY-COHERENT, DENSE FILAMENTS IN THE NORTHERN GALACTIC PLANE: AUTOMATED IDENTIFICATION USING MINIMUM SPANNING TREE

Large-scale gaseous filaments with lengths up to the order of 100 pc are on the upper end of the filamentary hierarchy of the Galactic interstellar medium (ISM). Their association with respect to the Galactic structure and their role in Galactic star formation are of great interest from both an observational and theoretical point of view. Previous “by-eye” searches, combined together, have started to uncover the Galactic distribution of large filaments, yet inherent bias and small sample size limit conclusive statistical results from being drawn. Here, we present (1) a new, automated method for identifying large-scale velocity-coherent dense filaments, and (2) the first statistics and the Galactic distribution of these filaments. We use a customized minimum spanning tree algorithm to identify filaments by connecting voxels in the position–position–velocity space, using the Bolocam Galactic Plane Survey spectroscopic catalog. In the range of , we have identified 54 large-scale filaments and derived mass ( ), length (10–276 pc), linear mass density (54–8625 pc−1), aspect ratio, linearity, velocity gradient, temperature, fragmentation, Galactic location, and orientation angle. The filaments concentrate along major spiral arms. They are widely distributed across the Galactic disk, with 50% located within ±20 pc from the Galactic mid-plane and 27% run in the center of spiral arms. An order of 1% of the molecular ISM is confined in large filaments. Massive star formation is more favorable in large filaments compared to elsewhere. This is the first comprehensive catalog of large filaments that can be useful for a quantitative comparison with spiral structures and numerical simulations.
A systematic study of low-mass X-ray binaries in the M31 globular cluster system

We investigate low mass X-ray binaries (LMXBs) in the M31 globular cluster (GC) system using data from the 2XMMi catalogue. These X-ray data are based on all publicly available XMM-Newton observations of the galaxy. This new survey provides the most complete and homogeneous X-ray survey of M31’s GCs to date, covering > 80% of the confirmed old clusters in the galaxy. We associate 41 X-ray sources with confirmed old clusters in the M31 cluster catalogue of Peacock et al. (2010). Comparing these data with previous surveys of M31, it is found that three of these clusters are newly identified, including a bright transient source in the cluster B128. Four additional clusters, that are not detected in these 2XMMi data, have previously been associated with X-ray sources from Chandra or ROSAT observations. Including these clusters, we identify 45 clusters in M31 which are associated with X-ray emission. By considering the latest optical GC catalogues, we identify that three of the previously proposed X-ray clusters are likely to be background galaxies and two have stellar profiles. We consider the properties of LMXB-hosting clusters and confirm significant trends between the presence of an LMXB and the metallicity, luminosity and stellar collision rate of a cluster. We consider the relationship between the luminosity and stellar collision rate of a cluster and note that LMXB hosting clusters have higher than average stellar collision rates for their mass. Our findings strongly suggest that the stellar collision rate is the dominant parameter related to the presence of LMXBs. This is consistent with the formation of LMXBs in GCs through dynamical interactions.
Investigating magnetic activity in very stable stellar magnetic fields: long-term photometric and spectroscopic study of the fully convective M4 dwarf V374 Peg

The ultrafast-rotating ($P_\mathrm{rot}\approx0.44 d$) fully convective single M4 dwarf V374 Peg is a well-known laboratory for studying intense stellar activity in a stable magnetic topology. As an observable proxy for the stellar magnetic field, we study the stability of the light curve, and thus the spot configuration. We also measure the occurrence rate of flares and coronal mass ejections (CMEs). We analyse spectroscopic observations, $BV(RI)_C$ photometry covering 5 years, and additional $R_C$ photometry that expands the temporal base over 16 years. The light curve suggests an almost rigid-body rotation, and a spot configuration that is stable over about 16 years, confirming the previous indications of a very stable magnetic field. We observed small changes on a nightly timescale, and frequent flaring, including a possible sympathetic flare. The strongest flares seem to be more concentrated around the phase where the light curve indicates a smaller active region. Spectral data suggest a complex CME with falling-back and re-ejected material, with a maximal projected velocity of $\approx$675km/s. We observed a CME rate much lower than expected from extrapolations of the solar flare-CME relation to active stars.
VERTICAL EQUILIBRIUM, ENERGETICS, AND STAR FORMATION RATES IN MAGNETIZED GALACTIC DISKS REGULATED BY MOMENTUM FEEDBACK FROM SUPERNOVAE

Recent hydrodynamic (HD) simulations have shown that galactic disks evolve to reach well-defined statistical equilibrium states. The star formation rate (SFR) self-regulates until energy injection by star formation feedback balances dissipation and cooling in the interstellar medium (ISM), and provides vertical pressure support to balance gravity. In this paper, we extend our previous models to allow for a range of initial magnetic field strengths and configurations, utilizing three-dimensional, magnetohydrodynamic (MHD) simulations. We show that a quasi-steady equilibrium state is established as rapidly for MHD as for HD models unless the initial magnetic field is very strong or very weak, which requires more time to reach saturation. Remarkably, models with initial magnetic energy varying by two orders of magnitude approach the same asymptotic state. In the fully saturated state of the fiducial model, the integrated energy proportions E turb : E th : δ E mag : E ¯ mag ? > are 0.35:0.39:0.15:0.11, while the proportions of midplane support P turb : P th : δ &Pgr; mag : &Pgr; ¯ mag ? > are 0.49:0.18:0.18:0.15. Vertical profiles of total effective pressure satisfy vertical dynamical equilibrium with the total gas weight at all heights. We measure the “feedback yields” &eegr; c ≡ P c / &Sgr; SFR ? > (in suitable units) for each pressure component, finding that &eegr; turb ∼ 3.5 − 4 ? > and &eegr; th ∼ 1.1 − 1.4 ? > are the same for MHD as in previous HD simulations, and δ &eegr; mag ∼ 1.3 − 1.5 . > These yields can be used to predict the equilibrium SFR for a local region in a galaxy based on its observed gas and stellar surface densities and velocity dispersions. As the ISM weight (or dynamical equilibrium pressure) is fixed, an increase in η from turbulent magnetic fields reduces the predicted &Sgr; SFR ? > by ∼ 20 − 30 % ? > relative to the HD case.
Average extinction curves and relative abundances for quasi-stellar object absorption-line systems at 1 ≤zabs < 2

We have studied a sample of 809 Mg II absorption systems with 1.0 ≤ z abs ≤ 1.86 in the spectra of Sloan Digital Sky Survey quasi-stellar objects (QSOs), with the aim of understanding the nature and abundance of the dust and the chemical abundances in the intervening absorbers. Normalized, composite spectra were derived, for abundance measurements, for the full sample and several subsamples, chosen on the basis of the line strengths and other absorber and QSO properties. Average extinction curves were obtained for the subsamples by comparing their geometric mean spectra with those of matching samples of QSOs without absorbers in their spectra. There is clear evidence for the presence of dust in the intervening absorbers. The 2175-A feature is not present in the extinction curves, for any of the subsamples. The extinction curves are similar to the Small Magellanic Cloud (SMC) extinction curve with a rising ultraviolet (UV) extinction below 2200 A. The absorber rest-frame colour excess, E(B - V), derived from the extinction curves, depends on the absorber properties and ranges from <0.001 to 0.085 for various subsamples. The column densities of Mg II, Al II, Si II, Ca II, Ti II, Cr II, Mn II, Fe II, Co II, Ni II and Zn II do not show such a correspondingly large variation. The overall depletions in the high E(B - V) samples are consistent with those found for individual damped Lyman a systems, the depletion pattern being similar to halo clouds in the Galaxy. Assuming an SMC gas-to-dust ratio, we find a trend of increasing abundance with decreasing extinction; systems with N H1 ∼ 10 20 cm -2 show solar abundance of Zn. The large velocity spread of strong Mg II systems seems to be mimicked by weak lines of other elements. The ionization of the absorbers, in general appears to be low: the ratio of the column densities of Al III to Al II is always less than 1/2. QSOs with absorbers are, in general, at least three times as likely to have highly reddened spectra as compared to QSOs without any absorption systems in their spectra.