Miracle-dz/UniFAR-FTUs huggingface dataset:
Chaotic mixing using micro-rotors in a confined domain

In this work we study chaotic mixing induced by point micro-rotors in a bounded two dimensional Stokes flow. The dynamics of the pair of rotors, modeled as rotlets, are non Hamiltonian in the bounded domain and produce chaotic advection of fluid tracers in subsets of the domain. A complete parametric investigation of the fluid mixing as a function of the initial locations of the rotlets is performed based on pseudo phase portraits. The mixing of fluid tracers as a function of relative positions of micro-rotors is studied using finite time entropy and locational entropy. The finite time locational entropy is used to identify regions of the fluid that produce good vs poor mixing and this is visualized by the stretching and folding of blobs of tracer particles. Unlike the case of the classic blinking vortex dynamics, the velocity field of the flow modeled using rotlets inside a circular boundary is smooth in time and satisfies the no slip boundary condition. This makes the considered model a more realistic case for studies of mixing in microfluidic devices using magnetic actuated microspheres.
On the origin of the FeK$\alpha$ line in the Seyfert 2 galaxy NGC 7172

The Seyfert 2 Galaxy NGC 7172 was observed twice by BeppoSAX narrow eld instruments approx- imately one year apart. As found in previous observations, the source is variable on short time scales (hours) by a factor of30%, conrming the presence of a type 1 nucleus at the center. A strong flux variability (by a factor of 2) on a longer time scale was observed between the two observations. Indeed, in November 1997, the lowest flux ever recorded was detected by BeppoSAX. The broad band spectra obtained with the BeppoSAX narrow eld instruments show marginal evidence of a reflection component. This structure could explain the very flat spectra previously observed in the 2{10 keV band. An FeK line was also detected in both observations. The line intensity appears to remain almost constant between the two observations even if the associated large errors cannot exclude some variability. In order to understand the problem of the origin of the line, data from previous observations, performed with other satellites, were also used. The scenario favored is one where the line is produced at a distance of approximatively 8 light years from the continuum source region, rather than having its origin in the accretion disk. In the framework of the standard unied models for AGN, this suggests that its origin is located in the molecular torus.
Gauge invariant wave equations in curved space-times and primordial magnetic fields

The inflationary production of magnetic field seeds for galaxies is discussed. The analysis is carried out by writing the wave equation of the electromagnetic field in curved space-times. The conformal invariance is broken by taking into account the interaction of the electromagnetic field with the curvature tensor of the form $\ensuremath{\lambda}{R}_{\ensuremath{\alpha}\ensuremath{\beta}\ensuremath{\gamma}\ensuremath{\delta}}{F}^{\ensuremath{\alpha}\ensuremath{\beta}}{F}^{\ensuremath{\gamma}\ensuremath{\delta}}$. Such a term induces an amplification of the magnetic field during the reheating phase of the universe, but no growth of the magnetic field occurs in the de Sitter epoch. The resulting primordial magnetic field turns out to have strengths of astrophysical interest.
Energizing the last phase of common-envelope removal

We propose a scenario where a companion that is about to exit a common envelope evolution (CEE) with a giant star accretes mass from the remaining envelope outside its deep orbit and launches jets that facilitate the removal of the remaining envelope. The jets that the accretion disk launches collide with the envelope and form hot bubbles that energize the envelope. Due to gravitational interaction with the envelope, that might reside in a circumbinary disk, the companion migrates further in, but the inner boundary of the circumbinary disk continues to feed the accretion disk. While near the equatorial plane mass leaves the system at a very low velocity, along the polar directions velocities are very high. When the primary is an asymptotic giant branch star, this type of flow forms a bipolar nebula with very narrow waists. We compare this envelope removal process with four others last-phase common envelope removal processes. We also note that the accreted gas from the envelope outside the orbit in the last-phase of the CEE might carry with it angular momentum that is antialigned to the orbital angular momentum. We discuss the implications to the possibly antialigned spins of the merging black hole event GW170104.
The disc-averaged star formation relation for Local Volume dwarf galaxies

Spatially resolved HI studies of dwarf galaxies have provided a wealth of precision data. However these high-quality, resolved observations are only possible for handful of dwarf galaxies in the Local Volume. Future HI surveys are unlikely to improve the current situation. We therefore explore a method for estimating the surface density of the atomic gas from global HI parameters, which are conversely widely available. We perform empirical tests using galaxies with resolved HI maps, and find that our approximation produces values for the surface density of atomic hydrogen within typically 0.5dex of the true value. We apply this method to a sample of 147 galaxies drawn from modern near-infrared stellar photometric surveys. With this sample we confirm a strict correlation between the atomic gas surface density and the star formation rate surface density, that is vertically offset from the Kennicutt-Schmidt relation by a factor of 10-30, and significantly steeper than the classical N=1.4 of Kennicutt (1998). We further infer the molecular fraction in the sample of low surface brightness, predominantly dwarf galaxies by assuming that the star formation relationship with molecular gas observed for spiral galaxies also holds in these galaxies, finding a molecular-to-atomic gas mass fraction within the range of 5-15%. Comparison of the data to available models shows that a model in which the thermal pressure balances the vertical gravitational field captures better the shape of the $\Sigma_{\rm SFR}-\Sigma_{\rm gas}$ relationship. However, such models fail to reproduce the data completely, suggesting that thermal pressure plays an important role in the disks of dwarf galaxies.
Evolution of magnetized, differentially rotating neutron stars: Simulations in full general relativity

We study the effects of magnetic fields on the evolution of differentially rotating neutron stars, which can be formed in stellar core collapse or binary neutron star coalescence. Magnetic braking and the magnetorotational instability (MRI) both act on differentially rotating stars to redistribute angular momentum. Simulations of these stars are carried out in axisymmetry using our recently developed codes which integrate the coupled Einstein-Maxwell-MHD equations. We consider stars with two different equations of state (EOS), a gamma-law EOS with $\ensuremath{\Gamma}=2$, and a more realistic hybrid EOS, and we evolve them adiabatically. Our simulations show that the fate of the star depends on its mass and spin. For initial data, we consider three categories of differentially rotating, equilibrium configurations, which we label normal, hypermassive and ultraspinning. Normal configurations have rest masses below the maximum achievable with uniform rotation, and angular momentum below the maximum for uniform rotation at the same rest mass. Hypermassive stars have rest masses exceeding the mass limit for uniform rotation. Ultraspinning stars are not hypermassive, but have angular momentum exceeding the maximum for uniform rotation at the same rest mass. We show that a normal star will evolve to a uniformly rotating equilibrium configuration. An ultraspinning star evolves to an equilibrium state consisting of a nearly uniformly rotating central core, surrounded by a differentially rotating torus with constant angular velocity along magnetic field lines, so that differential rotation ceases to wind the magnetic field. In addition, the final state is stable against the MRI, although it has differential rotation. For a hypermassive neutron star, the MHD-driven angular momentum transport leads to catastrophic collapse of the core. The resulting rotating black hole is surrounded by a hot, massive, magnetized torus undergoing quasistationary accretion, and a magnetic field collimated along the spin axis\char22{}a promising candidate for the central engine of a short gamma-ray burst.
Probing the classical field approximation—thermodynamics and decaying vortices

We review our version of the classical field approximation to the dynamics of a finite-temperature Bose gas. In the case of a periodic box potential, we investigate the role of the high-momentum cut-off, essential in the method. In particular, we show that the cut-off going to the infinity limit describes the particle number going to infinity with the scattering length going to zero. In this weak-interaction limit, the relative population of the condensate tends to unity. We also show that the cross-over energy, at which the probability distribution of the condensate occupation changes its character, grows with a growing scattering length. In the more physical case of the condensate in the harmonic trap we investigate the dissipative dynamics of a vortex. We compare the decay time and the velocities of the vortex with the available analytic estimates.
Density profiles of ultracompact minihalos: Implications for constraining the primordial power spectrum

Enhanced density fluctuations on small scales would lead to the formation of numerous dark matter minihalos, so limits on the minihalo abundance can place upper bounds on the small-scale primordial power spectrum. In particular, the ultracompact minihalo (UCMH), a dark matter structure hypothesized to possess a $\rho\propto r^{-9/4}$ density profile due to its formation at $z\geq 1000$, has been used to establish an upper bound on the primordial power spectrum at scales smaller than 2 Mpc. The extreme slope of this density profile amplifies the observational signals of UCMHs. However, we recently showed via N-body simulations that the $\rho\propto r^{-9/4}$ density profile does not develop in realistic formation scenarios, throwing UCMH-derived power spectrum constraints into question. Instead, minihalos develop shallower inner profiles with power-law indices between $-3/2$ and $-1$. In this paper, we expand on that result and discuss its implications. Using a model that is calibrated to simulation results and predicts halo structures in spiked power spectra based on their formation times, we calculate new upper bounds on the primordial power spectrum based on limits on the dark matter annihilation rate within the Galaxy. We find that despite assuming shallower profiles, this minihalo model actually yields stronger constraints than the previous UCMH picture owing to its inclusion of all minihalos instead of only the earliest-forming ones.
The Orbital Parameters of the Eclipsing High-mass X-Ray Binary Pulsar IGR J16493–4348 from Pulsar Timing

IGR J16493–4348 is an eclipsing supergiant high-mass X-ray binary (sgHMXB), where accretion onto the compact object occurs via the radially outflowing stellar wind of its early B-type companion. We present an analysis of the system’s X-ray variability and periodic modulation using pointed observations (2.5–25 keV) and Galactic bulge scans (2–10 keV) from the Rossi X-ray Timing Explorer (RXTE) Proportional Counter Array (PCA), along with Swift Burst Alert Telescope (BAT) 70-month snapshot (14–195 keV) and transient monitor (15–50 keV) observations. The orbital eclipse profiles from the PCA scan and BAT light curves are modeled using asymmetric and symmetric step and ramp functions. We obtain an improved orbital period measurement of 6.7828 ± 0.0004 days from an observed minus calculated (O–C) analysis of mid-eclipse times derived from the BAT transient monitor and PCA scan data. No evidence is found for the presence of a strong photoionization or accretion wake. We refine the superorbital period to 20.067 ± 0.009 days from the discrete Fourier transform (DFT) of the BAT transient monitor light curve. A pulse period of 1093.1036 ± 0.0004 s is measured from a pulsar timing analysis using pointed PCA observations spanning ∼1.4 binary orbits. We present pulse times of arrival (ToAs), circular and eccentric timing models, and calculations of the system’s Keplerian binary orbital parameters. We derive an X-ray mass function of M⊙ and find a spectral type of B0.5 Ia for the supergiant companion through constraints on the mass and radius of the donor. Measurements of the eclipse half-angle and additional parameters describing the system geometry are provided.
Macroscopic Observables

We study macroscopic observables deﬁned as the total value of a physical quantity over a collection of quantum systems. We show that previous results obtained for inﬁnite ensemble of identically prepared systems lead to incorrect conclusions for ﬁnite ensembles. In particular, exact measurement of a macroscopic observable signiﬁcantly disturbs the state of any ﬁnite ensemble. However, we show how this disturbance can be made arbitrarily small when the measurement are of ﬁnite accuracy. We demonstrate a tradeoﬀ between state disturbance and measurement coarseness as a function of the size of the ensemble. Using this tradeoﬀ, we show that the histories generated by any sequence of ﬁnite accuracy macroscopic measurements always generate a consistent family in the absence of large scale entanglement, for suﬃciently large ensembles. Hence, macroscopic observables behave “classically” provided that their accuracy is coarser than the quantum correlation length-scale of the system. The role of these observable is also discussed in the context of NMR quantum information processing and bulk ensemble quantum state tomography.
OXYGEN ABUNDANCES IN LOW SURFACE BRIGHTNESS DISK GALAXIES

The oxygen abundances in the \HII regions of a sample of low surface brightness (LSB) disk galaxies are presented. In general, LSB galaxies are found to be metal poor ($Z < {1 \over 3} Z\solar$). Indeed, some LSB galaxies rival the lowest abundance extragalactic objects known. These low metallicities indicate that LSB galaxies evolve slowly, forming relatively few stars over a Hubble time. The low metallicities of LSB galaxies occur even though many are comparable in size and mass to the prominent spirals which define the Hubble sequence. As well as being low in surface brightness, these galaxies tend to be isolated. This suggests that surface mass density and environment are more relevant to galaxy evolution than gross size. Despite the low surface brightness of the disks, massive ($M > 60 M\solar$) stars are inferred to be present and no abnormality of the IMF is indicated. Many low excitation \HII regions exist at low metallicity in LSB galaxies, and the ionization parameter is not tightly correlated with metallicity. However, there does seem to be a significant envelope of maximum ionization at a given metallicity.
Bohmian mechanics for instrumentalists

We formulate Bohmian mechanics (BM) such that the main objects of concern are macroscopic phenomena, while microscopic particle trajectories only play an auxiliary role. Such a formulation makes it easy to understand why BM always makes the same measurable predictions as standard quantum mechanics (QM), irrespective of the details of microscopic trajectories. Relativistic quantum field theory (QFT) is interpreted as an effective long-distance theory that at smaller distances must be replaced by some more fundamental theory. Analogy with condensed-matter physics suggests that this more fundamental theory could have a form of nonrelativistic QM, offering a simple generic resolution of an apparent conflict between BM and relativistic QFT.
Cepheid Calibration of the Peak Brightness of Type Ia Supernovae. XI. SN 1998aq in NGC 3982

Repeated imaging observations have been made of NGC 3982 with the Hubble Space Telescope between 2000 March and May, over an interval of 53 days. Images were obtained on 12 epochs in the F555W band and on five epochs in the F814W band. The galaxy hosted the Type Ia supernova (SN Ia) SN 1998aq. A total of 26 Cepheid candidates were identified, with periods ranging from 10 to 45 days, using photometry with the DoPHOT program. The dereddened distance to NGC 3982 is estimated from these data using various criteria to maximize signal-to-noise ratio and reliability: the values lie between 31.71 and 31.82, with uncertainties in the mean of typically ±0.14 mag for each case. A parallel analysis using photometry with HSTphot discovered 13 variables, yielding a distance modulus of 31.85 ± 0.16. The final adopted modulus is (M-m)0 = 31.72 ± 0.14 (22 ± 1.5 Mpc). Photometry of SN 1998aq that is available in the literature is used in combination with the derived distance to NGC 3982 to obtain the peak absolute magnitude of this supernova. The lower limit (no extinction within the host galaxy) for MV is -19.47 ± 0.15 mag. Corrections for decline rate and intrinsic color to carry these to the reduced system of Parodi and collaborators have been performed. The derived luminosities at hand are fully consistent with the mean of the eight normal SNe Ia previously calibrated with Cepheids. Together they yield H0 ≈ 60 ± 2(internal) km s-1 Mpc-1 based on an assumed LMC distance modulus of 18.50. We point out that correcting some of the systematic errors and including uncertainty estimates due to them leads to H0 = 58.7 ± 6.3(internal) km s-1 Mpc-1.
Twin Peaks kHz QPOs : Mathematics of the 3:2 Orbital Resonance

Using the method of multiple scales, one can derive an analytic solution that describes the behaviour of weakly coupled, non-linear oscillations in nearly Keplerian discs around neutron stars or black holes close to the 3:2 orbital epicyclic resonance. The obtained solution agrees with a previous numerical simulation. Such a result may be relevant to the kilohertz quasi-periodic variability in X-ray fluxes observed in many Galactic black hole and neutron star sources. With a particular choice of tunable parameters, the solution fits accurately the observational data for Sco X-1.
Observations of Seyfert Galaxies by OSSE and Parameters of Their X-Ray/Gamma-Ray Sources

We present a summary of spectra of Seyfert galaxies observed by the OSSE detector aboard Compton Gamma Ray Observatory. We obtain average spectra of Seyfert galaxies of types 1 and 2 and find they are well fitted by thermal Comptonization. We present detailed parameter ranges for the plasma temperature and the Compton parameter in the cases of spherical and slab geometries. We find both the average and individual OSSE spectra of Seyfert 2s are significantly harder than those of Seyfert 1s, which difference can be due to anisotropy of Compton reflection and/or Thomson-thick absorption.
Conical diffraction in honeycomb lattices

Received 16 March 2009; published 18 May 2009Conical diffraction in honeycomb lattices is analyzed. This phenomenon arises in nonlinear Schrodingerequations with honeycomb lattice potentials. In the tight-binding approximation the wave envelope is governedby a nonlinear classical Dirac equation. Numerical simulations show that the Dirac equation and the latticeequation have the same conical diffraction properties. Similar conical diffraction occurs in both the linear andnonlinear regimes. The Dirac system reveals the underlying mechanism for the existence of conical diffractionin honeycomb lattices.DOI: 10.1103/PhysRevA.79. 053830 PACS number s : 42.65. Tg, 42.70. Qs
First-principles results for electromagnetic properties of sd shell nuclei

In this work we present $ab~initio$ shell-model calculations for electric quadrupole moments and magnetic dipole moments of $sd$ shell nuclei using valence-space Hamiltonians derived with two $ab~initio$ approaches: the in-medium similarity renormalization group (IM-SRG) and the coupled-cluster effective interaction (CCEI). Results are in a reasonable agreement with the available experimental data as well as with the results from the phenomenological USDB effective interaction. This work will add more information to the available $ab~initio$ results for the spectroscopy of $sd$ shell nuclei.
VELOCITY BIAS IN CLUSTERS

Hierarchical gravitational clustering creates galaxies that usually do not fully share the dynamical history of an average particle in the mass field. In particular, galaxy tracers identified in numerical simulations can have individual velocity dispersions in virialized regions a factor \bvs\ lower than the dark matter. The field average of the pairwise velocity dispersion depends on the statistical weighting of collapsed regions, so that the tracer pairwise dispersion is a different factor, \bvp, times the density field value. A model of a cool equilibrium tracer population demonstrates that mass to light segregation is very sensitive to single particle velocity bias. For the $\phi=-GM/(r+a)$ potential a $\bvs=0.9$ tracer indicates a virial mass about a factor of 5 low. The likely value of \bvs\ is estimated and the simple equilibrium model is tested for applicability using a $10^6$ particle simulation of the formation of a single cluster from cosmological initial conditions. From this simulation, the value of \bvs\ is estimated as $0.8\pm0.1$. The pairwise velocity dispersion bias, \bvp, which is equal to \bvs\ augmented with any anti-bias of galaxies against high velocity dispersion clusters. The value of \bvp\ is estimated to be 15\% less than \bvs, consequently $\bvp=0.6^{+0.2}_{-0.1}$. Comparison of cluster mass and luminosity profiles at large radii is a test for the existence of single particle velocity bias. [compressed postscript file cluster.ps. Z via anonymous ftp from this http URL in ~ftp/pub/hpcc, or carlberg@astro.this http URL]
Early asymmetric growth of planetary stagnant lids

Abstract Convection within planetary bodies is often modelled using a temperature-dependent rheology which, when cooled from the surface, naturally leads to the formation of a so-called stagnant lid at the cold outer surface. However, for sufficiently large planets the phase diagram describing the partially molten system may depend significantly on pressure in addition to temperature, leading to significant variations in solid fraction. The aggregate rheology may therefore exhibit significant dependence on both the temperature and pressure, and hence may exhibit marked dependence on depth in addition to the dependence on the thermal structure due to convection. Here, we consider the growth and stability of a planetary stagnant lid. We first characterise the effect of a pressure- and temperature-dependent rheology on the evolution of a symmetric, planetary stagnant lid. This analysis further suggests that the pressure dependence of the rheology may lead to an instability of the growing stagnant lid which, importantly, may lead to asymmetric lid growth. We find that the most unstable mode is at the longest wavelengths, and discuss the implications for stagnant-lid convection and the growth of asymmetric surfaces of planetary bodies. In particular, we discuss the possibility that this instability has implications for the formation of the crustal dichotomy found on the Moon.