Miracle-dz/UniFAR-FTUs huggingface dataset:
AGN feedback and multiphase gas in giant elliptical galaxies

Recent observations have found extended multi-phase gas in a significant fraction of massive elliptical galaxies. We perform high-resolution three-dimensional hydrodynamical simulations of two idealized elliptical galaxies -- one representing a typical galaxy characterized by initial conditions conducive to the development of thermal instability and the other one less likely to develop thermal instability -- in order to study the development of thermal instability and the formation of multi-phase structures. We analyze the interplay between radiative cooling, momentum-driven AGN feedback, star formation, and stellar feedback from both young and old stars. We find that in one class of elliptical galaxies, the entropy of the hot halo gas rises sharply as a function of radius, and the hot halo is thermally stable and run-away cooling can only happen in the very center of the galaxy. In other class of ellipticals, the hot halo gas has a cooling to free-fall time ratio close to 10, and the non-linear perturbation driven by AGN feedback can cause the hot gas to frequently precipitate into extended multi-phase filaments. Both multi- and single-phase elliptical galaxies experience cooling-driven AGN feedback cycles. Interestingly, AGN feedback maintains the multi- or single-phase nature of the halo but does not turn multi-phase galaxies into single-phase ones or vice versa. Some of the extended cold gas in the multi-phase galaxy also forms young stars. The level of star formation and its spatial distribution are in excellent agreement with {\it Hubble} observations of nearby elliptical galaxies.
On a Model of Magnetically Charged Black Hole with Nonlinear Electrodynamics

The Bronnikov model of nonlinear electrodynamics is investigated in general relativity. The magnetic black hole is considered and we obtain a solution giving corrections to the Reissner-Nordstrom solution. In this model spacetime at r → ∞ becomes Minkowski’s spacetime. We calculate the magnetic mass of the black hole and the metric function. At some parameters of the model there can be one, two or no horizons. The Hawking temperature and the heat capacity of black holes are calculated. We show that a second-order phase transition takes place and black holes are thermodynamically stable at some range of parameters.
Binary black hole growth by gas accretion in stellar clusters

We show that binaries of stellar-mass black holes formed inside a young protoglobular cluster, can grow rapidly inside the cluster’s core by accretion of the intracluster gas, before the gas may be depleted from the core. A black hole with mass of the order of eight solar masses can grow to values of the order of thirty five solar masses in accordance with recent gravitational waves signals observed by LIGO. Due to the black hole mass increase, a binary may also harden. The growth of binary black holes in a dense protoglobular cluster through mass accretion indicates a potentially important formation and hardening channel.
Strain tuning and anisotropic spin correlations in iron-based systems

Nematic order in the iron-based superconductors is closely tied to a lattice distortion and a structural transition from tetragonal to orthorhombic symmetry. External stress of the appropriate symmetry acts as a conjugate field of the nematic order parameter and can be utilized to detwin nematic domains but also smears an otherwise sharp nematic transition. On the other hand, applying stress in proper symmetry channels allows one to tune the nematic phase transition. Recent experiments analyzed the stress-induced changes of the nematic and magnetic phase transition temperature. Here we show that the observed trends can be understood in terms of spin-induced nematicity. The strain sensitivity is shown to be a fluctuation effect. The strong sensitivity to antisymmetric strain is a consequence of the anisotropic nature of the magnetic excitation spectrum. The formalism presented here can be naturally generalized to determine the strain-sensitivity of vestigial phases related to other magnetic states that have been observed in the iron-based systems, such as e.g.\ the spin-charge density wave and the spin-vortex crystals.
Construction of nonsingular pre-big-bang and ekpyrotic cosmologies and the resulting density perturbations

We consider the construction of nonsingular Pre-Big-Bang and Ekpyrotic type cosmological models realized by the addition to the action of specific higher-order terms stemming from quantum corrections. We study models involving general relativity coupled to a single scalar field with a potential motivated by the Ekpyrotic scenario. We find that the inclusion of the string loop and quantum correction terms in the string frame makes it possible to obtain solutions of the variational equations which are nonsingular and bouncing in the Einstein frame, even when a negative exponential potential is present, as is the case in the Ekpyrotic scenario. We analyze the spectra of perturbations produced during the bouncing phase and find that the spectrum of curvature fluctuations in the model proposed originally to implement the Ekpyrotic scenario has a large blue tilt ($n_R= 3$). Except for instabilities introduced on small scales, the result agrees with what is obtained by imposing continuity of the induced metric and of the extrinsic curvature across a constant scalar field (up to $k^2$ corrections equal to the constant energy density) matching surface between the contracting and the expanding Einstein Universes. We also discuss nonsingular cosmological solutions obtained when a Gauss-Bonnet term with a coefficient suitably dependent on the scalar matter field is added to the action in the Einstein frame with a potential for the scalar field present.
A Data-driven Study of RR Lyrae Near-IR Light Curves: Principal Component Analysis, Robust Fits, and Metallicity Estimates

RR Lyrae variables are widely used tracers of Galactic halo structure and kinematics, but they can also serve to constrain the distribution of the old stellar population in the Galactic bulge. With the aim of improving their near-infrared photometric characterization, we investigate their near-infrared light curves, as well as the empirical relationships between their light curve and metallicities using machine learning methods. We introduce a new, robust method for the estimation of the light-curve shapes, hence the average magnitudes of RR Lyrae variables in the KS band, by utilizing the first few principal components (PCs) as basis vectors, obtained from the PC analysis of a training set of light curves. Furthermore, we use the amplitudes of these PCs to predict the light-curve shape of each star in the J-band, allowing us to precisely determine their average magnitudes (hence colors), even in cases where only one J measurement is available. Finally, we demonstrate that the KS-band light-curve parameters of RR Lyrae variables, together with the period, allow the estimation of the metallicity of individual stars with an accuracy of ∼0.2–0.25 dex, providing valuable chemical information about old stellar populations bearing RR Lyrae variables. The methods presented here can be straightforwardly adopted for other classes of variable stars, bands, or for the estimation of other physical quantities.
Quantum geometrodynamics for black holes and wormholes

The geometrodynamics of spherical gravity with a self-gravitating thin dust shell as a source is constructed. The shell Hamiltonian constraint is derived and the corresponding Schr\"odinger equation is obtained. This equation appears to be a finite difference equation. Its solutions are required to be analytic functions on the relevant Riemannian surface. The method of finding discrete spectra is suggested based on the analytic properties of the solutions. The large black hole approximation is considered and the discrete spectra for bound states of quantum black holes and wormholes are found. They depend on two quantum numbers and are, in fact, quasicontinuous.
Constraints on the Equation of State of Dark Energy and the Hubble Constant from Stellar Ages and the Cosmic Microwave Background

We place constraints on the redshift-averaged, effective value of the equation of state of dark energy, w, using only the absolute ages of Galactic stars and the observed position of the first peak in the angular power spectrum of the cosmic microwave background (CMB). We find w < -0.8 at the 68% confidence level. If we further consider that w ≥ -1, this finding suggests that within our uncertainties, dark energy is indistinguishable from a classical vacuum energy term. We detect a correlation between the ages of the oldest galaxies and their redshift. This opens up the possibility of measuring w(z) by computing the relative ages of the oldest galaxies in the universe as a function of redshift, dz/dt. We show that this is a realistic possibility by computing dz/dt at z ~ 0 from Sloan Digital Sky Survey (SDSS) galaxies and obtain an independent estimate for the Hubble constant, H0 = 69 ± 12 km s-1 Mpc-1. The small number of galaxies considered at z > 0.2 does not yield, currently, a precise determination of w(z), but shows that the age-redshift relation is consistent with a standard ΛCDM universe with w = -1.
Links between quasi-periodic oscillations and accretion states in neutron star low-mass X-ray binaries

We analysed the Rossi X-ray Timing Explorer data from a sample of bright accreting neutron star (NS) low-mass X-ray binaries (LMXBs). With the aim of studying the quasi-periodic variability as a function of the accretion regime, we carried out a systematic search of the quasi-periodic oscillations (QPOs) in the X-ray time series of these systems, using the integrated fractional variability as a tracker for the accretion states. We found that the three QPO types originally identified in the 1980s for the brightest LMXBs, the so-called Z sources, i.e. horizontal, normal and flaring branch oscillations (HBOs, NBOs and FBOs, respectively), are also identified in the slightly less bright NS LMXBs, the so-called atoll sources, where we see QPOs with a behaviour consistent with the HBOs and FBOs. We compared the quasi-periodic variability properties of our NS sample with those of a sample of black hole (BH) LMXBs. We confirm the association between HBOs, NBOs and FBOs observed in Z sources, with the type-C, type-B and type-A QPOs, respectively, observed in BH systems, and we extended the comparison to the HBO-like and FBO-like QPOs seen in atoll sources. We conclude that the variability properties of BH and weakly magnetized NS LMXBs show strong similarities, with QPOs only weakly sensitive to the nature of the central compact object in both classes of systems. We find that the historical association between kHz QPOs and high-frequency QPOs, seen around NSs and BHs, respectively, is not obvious when comparing similar accretion states in the two kinds of systems.
Detection of α Centauri at radio wavelengths: chromospheric emission and search for star–planet interaction

At radio wavelengths, solar type stars emit thermal free-free and gyroresonance, gyrosynchrotron, and impulsive coherent emission. Thermal free-free emission originates at layers where the optical depth is close to unit, while high brightness temperature, variable emission, can be due to flares via gyrosynchrotron emission. We observed the alf Cen system with the Australian Telescope Compact Array at 2 GHz for three days and 17 GHz for one day. Both stars have been detected at 17 GHz, while only an upper limit has been obtained at low frequency despite the longest integration time. The brightness temperatures are consistent with the temperature of the upper chromosphere of the Sun. Inverting the formulae of the free-free emission, the average electron density of the plasma has been inferred. The same procedure was applied to the data in the millimetre recently taken with ALMA. A comparison with the atmospheric solar models reveals a higher level of activity in alf Cen B, even if still at quiescent level. The non detection at low frequency allow us to put a lower limit in the filling factor of active regions. The claimed detection of an Earth size planet in close orbit to alf Cen B, although doubtful, open the opportunity to check the existence of Star-Planet Magnetic Interaction (SPMI). This could trigger Auroral Radio Emission due to Electron Cyclotron Maser in the stellar corona, similar to the Jupiter-Io interaction, which is very intense, polarized and highly beamed. However, no hints of SPMI has been found.
IMPROVEMENT OF THE SEMI-ANALYTICAL METHOD, FOR DETERMINING THE GEOMETRICALLY NON-LINEAR RESPONSE OF THIN STRAIGHT STRUCTURES. PART I: APPLICATION TO CLAMPED–CLAMPED AND SIMPLY SUPPORTED–CLAMPED BEAMS

Abstract In a previous series of papers (Benamar 1990 Ph.D. Thesis, University of Southampton ; Benamar et al. 1991 Journal of Sound and Vibration 149 , 179–195; 164 , 399–424 [1–3]) a general model based on Hamilton's principle and spectral analysis has been developed for non-linear free vibrations occurring at large displacement amplitudes of fully clamped beams and rectangular homogeneous and composite plates. The results obtained with this model corresponding to the first non-linear mode shape of a clamped–clamped (CC) beam and to the first non-linear mode shape of a CC plate are in good agreement with those obtained in previous experimental studies (Benamar et al. 1991 Journal of Sound and Vibration 149, 179–195; 164 , 399–424 [2, 3]). More recently, this model has been re-derived (Azar et al. 1999 Journal of Sound and Vibration 224 , 377–395; submitted [4, 5]) using spectral analysis, Lagrange's equations and the harmonic balance method, and applied to obtain the non-linear steady state forced periodic response of simply supported (SS), CC, and simply supported–clamped (SSC) beams. The practical application of this approach to engineering problems necessitates the use of appropriate software in each case or use of published tables of data, obtained from numerical solution of the non-linear algebraic system, corresponding to each problem. The present work was an attempt to develop a more practical simple “multi-mode theory” based on the linearization of the non-linear algebraic equations, written on the modal basis, in the neighbourhood of each resonance. The purpose was to derive simple formulae, which are easy to use, for engineering purposes. In this paper, two models are proposed. The first is concerned with displacement amplitudes of vibration W max / H , obtained at the beam centre, up to about 0·7 times the beam thickness and the second may be used for higher amplitudes W max / H up to about 1·5 times the beam thickness. This new approach has been successfully used in the free vibration case to the first, second and third non-linear modes shapes of CC beams and to the first non-linear mode shape of a CSS beam. It has also been applied to obtain the non-linear steady state periodic forced response of CC and CSS beams, excited harmonically with concentrated and distributed forces.
Information Flow in Finite Flocks with Topological Interactions.

We simulate the Vicsek model utilising topological neighbour interactions and estimate information theoretic quantities as a function of noise, the variability in the extent to which each animal aligns with its neighbours, and the flock direction. We show that these quantities, mutual information and global transfer entropy, are in fact dependent on observation time, and in comparison to the canonical Vicsek model which utilises range-based interactions, the topological variant converges to the long-term limiting behaviour with smaller observation windows. Finally, we show that in contrast to the metric model, which exhibits maximal information flow for the ordered regime, the topological model maintains this maximal information flow beyond the phase transition and into the disordered regime.
FC-nilpotent and FC-soluble groups

Let an element of a group be called an FC element if it has only a finite number of conjugates in the group. Baer(1) and Neumann (8) have discussed groups in which every element is FC, and called them FC-groups. Both Abelian and finite groups are trivially FC-groups; Neumann has studied the properties common to FC-groups and Abelian groups, and Baer the properties common to FC-groups and finite groups. Baer has also shown that, for an arbitrary group G, the set H1 of all FC elements is a characteristic subgroup. Haimo (3) has defined the FC-chain of a group G by Hi/Hi−1 is the subgroup of all FC elements in G/Hi−1.
A heuristic quantum theory of the integer quantum Hall effect

Contrary to common belief, the current emitted by a contact embedded in a two-dimensional electron gas (2DEG) is quantized in the presence of electric and magnetic fields. This observation suggests a simple, clearly defined model for the quantum current through a Hall device that does not invoke disorder or interactions as the cause of the integer quantum Hall effect (QHE), but is based on a proper quantization of the classical electron drift motion. The theory yields a quantitative description of the breakdown of the QHE at high current densities that is in agreement with experimental data. Furthermore, several of its key points are in line with recent findings of experiments that address the dependency of the QHE on the 2DEG bias voltage, results that are not easily explained within the framework of conventional QHE models.
Two roads to hydrodynamic effective actions: a comparison

Author(s): Haehl, Felix M; Loganayagam, R; Rangamani, Mukund | Abstract: We make a detailed comparison between two attempts in recent years to construct hydrodynamic effective actions: we compare our work [1-7] with that of Crossley-Glorioso-Liu [8] and Glorioso-Liu [9]. The general philosophy espoused by the two approaches has a degree of overlap, despite various differences. We will try to outline the similarities to eke out the general lessons that have been uncovered, hoping that it will ease the access to the subject for interested readers.
A study of singly deuterated cyclopropenylidene c-C3HD in the protostar IRAS 16293–2422

Cyclic-C3HD (c-C3HD) is a singly deuterated isotopologue of c-C3H2, which is one of the most abundant and widespread molecules in our Galaxy. We observed IRAS 16293-2422 in the 3 mm band with a single frequency setup using the EMIR heterodyne 3 mm receiver of the IRAM 30m telescope. We observed seven lines of c-C3HD and three lines of c-C3H2. Observed abundances are compared with astrochemical simulations using the NAUTILUS gas-grain chemical model. Our results clearly show that c-C3HD can be used as an important supplement for studying chemistry and physical conditions for cold environments. Assuming that the size of the protostellar envelope is 3000 AU and same excitation temperatures for both c-C3H2 and c-C3HD, we obtain a deuterium fraction of $14_{-3}^{+4}\%$.
Electronic properties of intercalation complexes of the transition metal dichalcogenides

Abstract Intercalation of the layer type transition metal dichalcogenides by a variety of organic molecules, alkali metals, or ‘3d’ transition metals, provides a powerful way to finely tune the electron occupation of the relatively narrow ‘d’ bands met in these solids. These transition metal dichalcogenides are highly anisotropic solids, sometimes referred to as ‘two-dimensional’ solids, and the intercalant molecules which are electron donors enter between the layers. This can result in profound changes in the electronic properties of the host lattice, and these changes can be understood in terms of charge transfer and increased interlayer separation. The phenomena discussed include optical properties, transport properties, super-conductivity, order-disorder phenomena and phase changes, staging, magnetic properties, metal-insulator transitions, Anderson localization, and fast-ion conduction. Some possible practical applications are also considered.
A Galaxy at z = 6.545 and Constraints on the Epoch of Reionization

We report the discovery of a Lyα-emitting galaxy at redshift z = 6.545 serendipitously identified in the course of spectroscopic follow-up of hard X-ray sources on behalf of the Serendipitous Extragalactic X-Ray Source Identification (SEXSI) survey. The line flux of the galaxy, 2.1 × 10-17 ergs cm-2 s-1, is similar to line fluxes probed by narrowband imaging surveys; the 5.2 arcmin2 surveyed implies a surface density of z ≈ 6.5 Lyα emitters somewhat higher than that inferred from narrowband surveys. This source marks the sixth Lyα-emitting galaxy identified at z ≈ 6.5, a redshift putatively beyond the epoch of reionization when the damping wings of the neutral hydrogen of the intergalactic medium is capable of severely attenuating Lyα emission. By comparing the Lyα luminosity functions at z ≈ 5.7 and z ≈ 6.5, we infer that the intergalactic medium may remain largely reionized from the local universe out to z ≈ 6.5.
Relationship between Human Resource Management Practices and Employee Engagemen

Purpose: Employee Engagement is mainstream attention for organizations in the current business scenario. The purpose of the current research focused on analysing the relationship between HRM Practices and Employee Engagement considering employees working in various IT industries, especially considering employees working in HR Department. Design/Methodology/Approach: The research was cross-sectional in nature and survey method was employed to collect the data. Exploratory Factor Analysis, Confirmatory Factor Analysis, Structural Equation Modelling were used to analyse the hypothesis. Data was collected among 345 employees employed in the HR department of various private sector organizations. Results: The model fit indices were adequate and acceptable. The model fit indices obtained were: CMIN/DF = 2.909; Goodness of Fit index (GFI) = 0.945; adjusted goodness of fit index (AGFI) = 0.909; incremental fit index (IFI) = 0.976; Tucker-Lewis index (TLI) = 0.981; comparative fit index (CFI) = 0.966; root mean square error of approximation (RMSEA) = 0.06. Findings: The results of the study disclose that HRM practices and Employee Engagement were related to each other. HRM practices in organizations empowered employees and made them more engaged to perform better in their job roles. The study results imply that HRM practices need to be considered as priority in business organizations for the long term success. Research Limitations: Non probabilistic sample method was adopted and it was possible to gather data only from 345 employees working in the HR Department of various private sector organizations. Practical Implications: Business organizations are constantly working towards adopting new strategies and programs in the workplace to empower employees and keep them engaged in their work roles and responsibilities. Therefore, organizations to focus on human resource management practices and implement them effectively to make their employees committed and engaged towards their job. In this context, the present research attempts to analyse the association between human resource practices and employee engagement. The results provide insights for business managers on the importance of having effective Human Resource practices to enhance employees level of engagement towards their work roles. Originality/ Value: Current research contributes to the existing literature on Human Resource Practices and Employee Engagement. While considering the current business scenario, it becomes very important to understand the role of human resource management practices on the engagement level of employees.