Miracle-dz/UniFAR-FTUs huggingface dataset:
Superfluid density and critical velocity near the fermionic Berezinskii-Kosterlitz-Thouless transition

We theoretically investigate superfluidity in a strongly interacting Fermi gas confined to two dimensions at finite temperature. Using a Gaussian pair fluctuation theory in the superfluid phase, we calculate the superfluid density and determine the critical temperature and chemical potential at the Berezinskii-Kosterlitz-Thouless transition. We propose that the transition can be unambiguously demonstrated in cold-atom experiments by stirring the superfluid Fermi gas using a red detuned laser beam, to identify the characteristic jump in the local Landau critical velocity at the superfluidnormal interface, as the laser beam moves across the cloud.
Nodeless superconductivity in the SnAs-based van der Waals-type superconductor NaSn2As2

We grew the single crystals of the SnAs-based van der Waals (vdW)-type superconductor NaSn2As2 and systematically measured its resistivity, specific heat, and ultralow-temperature thermal conductivity. The superconducting transition temperature of our single crystal is 0.3 K higher than that previously reported. A weak but intrinsic anomaly situated at 193 K is observed in both resistivity and specific heat, which likely arises from a charge-density-wave (CDW) instability. Ultralow-temperature thermal conductivity measurements reveal a fully gapped superconducting state with a negligible residual linear term in zero magnetic field, and the field dependence of further suggests NaSn2As2 is an s-wave superconductor.
Gain spectra in GaAs double−heterostructure injection lasers

Gain spectra for GaAs double−heterostructure junction lasers have been obtained with high resolution. This is accomplished by using an automated data aquisition system to analyze the Fabry−Perot resonance modulation in the spontaneous emission spectra. For active regions doped with Ge at a level of 4×1017 cm−3, the gain in the TE polarization at a fixed wavelength increases linearly with current, below lasing threshold. However, the peak gain (at a variable wavelength) increases slightly faster than linearly with current. The photon energy at which gain is a maximum increases logarithmically with current. Gain in the TM polarization depicts the same general behavior as that for the TE case, except that it is slightly less than the TE gain. It is concluded that for this particular doping the spectral gain characteristics are intermediate between those for undoped and heavily doped active regions. Above the threshold for lasing in the TE mode the TE gain spectra are well saturated, with new fine details rev.
2D Bayesian automated tilted-ring fitting of disc galaxies in large H I galaxy surveys: 2dbat

We present a novel algorithm based on a Bayesian method for 2D tilted-ring analysis of disk galaxy velocity fields. Compared to the conventional algorithms based on a chi-squared minimisation procedure, this new Bayesian-based algorithm suffers less from local minima of the model parameters even with highly multi-modal posterior distributions. Moreover, the Bayesian analysis, implemented via Markov Chain Monte Carlo (MCMC) sampling, only requires broad ranges of posterior distributions of the parameters, which makes the fitting procedure fully automated. This feature will be essential when performing kinematic analysis on the large number of resolved galaxies expected to be detected in neutral hydrogen (HI) surveys with the Square Kilometre Array (SKA) and its pathfinders. The so-called '2D Bayesian Automated Tilted-ring fitter' (2DBAT) implements Bayesian fits of 2D tilted-ring models in order to derive rotation curves of galaxies. We explore 2DBAT performance on (a) artificial HI data cubes built based on representative rotation curves of intermediate-mass and massive spiral galaxies, and (b) Australia Telescope Compact Array (ATCA) HI data from the Local Volume HI Survey (LVHIS). We find that 2DBAT works best for well-resolved galaxies with intermediate inclinations (20 deg < i < 70 deg), complementing three-dimensional techniques better suited to modelling inclined galaxies.
Wind inhibition by X-ray irradiation in HMXBs: the influence of clumping and the final X-ray luminosity

Context. In wind-powered X-ray binaries, the radiatively driven stellar wind from the primary may be inhibited by the X-ray irradiation. This creates the feedback that limits the X-ray luminosity of the compact secondary. Wind inhibition might be weakened by the effect of small-scale wind inhomogeneities (clumping) possibly affecting the limiting X-ray luminosity. Aims. We study the influence of X-ray irradiation on the stellar wind for different radial distributions of clumping. Methods. We calculate hot star wind models with external irradiation and clumping using our global wind code. The models are calculated for different parameters of the binary. We determine the parameters for which the X-ray wind ionization is so strong that it leads to a decrease of the radiative force. This causes a decrease of the wind velocity and even of the mass-loss rate in the case of extreme X-ray irradiation. Results. Clumping weakens the effect of X-ray irradiation because it favours recombination and leads to an increase of the wind mass-loss rate. The best match between the models and observed properties of high-mass X-ray binaries (HMXBs) is derived with radially variable clumping. We describe the influence of X-ray irradiation on the terminal velocity and on the mass-loss rate in a parametric way. The X-ray luminosities predicted within the Bondi-Hoyle-Lyttleton theory agree nicely with observations when accounting for X-ray irradiation. Conclusions. The ionizing feedback regulates the accretion onto the compact companion resulting in a relatively stable X-ray source. The wind-powered accretion model can account for large luminosities in HMXBs only when introducing the ionizing feedback. There are two possible states following from the dependence of X-ray luminosity on the wind terminal velocity and mass-loss rate. One state has low X-ray luminosity and a nearly undisturbed wind, and the second state has high X-ray luminosity and exhibits a strong influence of X-rays on the flow.
Dense Molecular Gas in the Starburst Nucleus of NGC 1808

Dense molecular gas tracers in the central 1 kpc region of the superwind galaxy NGC 1808 have been imaged by ALMA at a resolution of 1″ (∼50 pc). Integrated intensities and line intensity ratios of HCN (1–0), H13CN (1–0), HCO+ (1–0), H13CO+ (1–0), HOC+ (1–0), HCO+ (4–3), CS (2–1), C2H (1–0), and previously detected CO (1–0) and CO (3–2) are presented. SiO (2–1) and HNCO (4–3) are detected toward the circumnuclear disk (CND), indicating the presence of shocked dense gas. There is evidence that an enhanced intensity ratio of HCN (1–0)/HCO+ (1–0) reflects star formation activity, possibly in terms of shock heating and electron excitation in the CND and a star-forming ring at radius ∼300 pc. A non-local thermodynamic equilibrium analysis indicates that the molecular gas traced by HCN, H13CN, HCO+, and H13CO+ in the CND is dense ( ) and warm (20 K ≲ Tk ≲ 100 K). The calculations yield a low average gas density of for a temperature of in the nuclear outflow. Dense gas tracers HCN (1–0), HCO+ (1–0), CS (2–1), and C2H (1–0) are detected for the first time in the superwind of NGC 1808, confirming the presence of a velocity gradient in the outflow direction.
Condensation energy in strongly coupled superconductors

We consider the condensation energy E c of strongly coupled magnetically mediated superconductors within the context of the spin-fermion model. We argue that the actual physics behind the condensation energy is much richer than in BCS theory, and that it is vital to take both the fermionic and bosonic contributions to the condensation energy into account. We argue that at strong coupling λ >> 1, the gain in the condensation energy is a result of the feedback on spin excitations, while the fermionic contribution to E c is positive due to an "undressing" feedback on the fermions. In addition we argue that the same feedback effect accounts for a gain in the kinetic energy at strong coupling. We also found that the BCS relation E c Δ 2 , where A is the pairing gap, only holds for λ ≤ 1. At larger λ, Δ keeps increasing and eventually saturates, while E c passes through a maximum at λ∼2 and then exhibits a decrease in the strong-coupling regime.
The VIMOS Ultra Deep Survey: On the nature, ISM properties, and ionizing spectra of CIII]1909 emitters at z=2-4

Context: Ultraviolet (UV) emission lines spectra are used to spectroscopically-confirm high-z galaxies and increasingly also to determine their physical properties. Aims: To interpret the observed UV spectra of distant galaxies in terms of the dominant radiation field and the physical condition of the interstellar medium. Methods: We construct a large grid of photoionization models and derive new spectral UV line diagnostics using equivalent widths (EWs) of CIII]1909 doublet, CIV1549 doublet and the line ratios of CIII], CIV, and HeII1640 recombination line. We apply these diagnostics to a sample of 450 CIII]-emitting galaxies at z=2-4 identified in the VIMOS Ultra Deep Survey by Le Fevre et al. (2017). Results: We show that the average star-forming galaxy (EW(CIII])~2A) is well described by stellar photoionization from single and binary stars. The inferred metallicity and ionization parameter is typically Z=0.3-0.5Zsun and logU=-2.7 to -3, in agreement with earlier work at similar redshifts. The models also indicate an average age of 50-200Myr since the beginning of the current star-formation, and an ionizing photon production rate, xi_ion, of log(xi_ion)~25.4Hz/erg. Among the sources with EW(CIII])=10-20A, ~30% are likely AGNs. Their derived metallicity is low, Z=0.02-0.2Zsun, and the ionization parameter higher (logU=-1.7). To explain the average UV observations of the strongest but rarest CIII] emitters (EW(CIII])>20A), we find that stellar photoionization is clearly insufficient. A radiation field consisting of a mix of a young stellar population (log(xi_ion)=25.6-25.8Hz/erg) plus an AGN component is required. Furthermore an enhanced C/O abundance ratio is needed for metallicities Z=0.1-0.2Zsun and logU=-1.7 to -1.5. Conclusions: The UV diagnostics we propose should serve as an important basis for the interpretation of observations of high redshift galaxies. [abridged]
Nonlinear microscopic relaxation of uniform magnetization precession

Dynamic relaxation for nonlinear magnetization excitation is analyzed. For direct processes, such as magnon–electron scattering and two-magnon scattering, the relaxation rate is determined from the linear case simply by utilizing the magnetization oscillation frequency for nonlinear excitation. For an indirect process, such as slow-relaxing impurities, the analysis gives an additional relaxation term proportional to the excitation level. In all cases the effective magnetization damping is increased compared to Landau–Lifshitz–Gilbert damping.
A catalog of spectroscopic binary candidate stars derived from a comparison of Gaia DR2 with other radial velocity catalogs

Using the recently published Gaia second data release which includes measurements of the mean radial velocity of about 7.2 million stars, we performed a systematic comparison with other existing radial velocity catalogues in order to search for variations in the radial velocity measurements, with the goal that detected differences may indicate that these stars are possibly spectroscopic binaries stars with only one visible component (SB1). We present a spectroscopic binary candidate stars catalogue containing 35,246 stars, compiled to encourage follow-up observations obtaining spectra at different epochs of these stars orbits in order to verify their binarity and to study these systems using radial velocity curves. Comparing the Gaia DR2 database with the K-M dwarf catalogue we found 16 stars that show radial velocity variations. In a comparison with the Pulkovo radial velocity catalogue of Hipparcos stars we identified a total of 539 SB1 candidate stars. In the largest radial velocity catalogue available, the RAVE catalogue, we found a total of 34,691 stars that show radial velocity variations when compared to the Gaia DR2 data.
Linear viscoelasticity of entangled wormlike micelles bridged by telechelic polymers: An experimental model for a double transient network

We survey the linear viscoelasticity of a new type of transient network: bridged wormlike micelles, whose structure has been characterized recently by Ramos and Ligoure [Macromolecules 40, 1248–1251 (2007)]. This composite material is obtained by adding telechelic copolymers (water-soluble chains with hydrophobic stickers at each extremity) to a solution of entangled wormlike micelles (WM). For comparison, naked WM and WM decorated by amphiphilic copolymers are also investigated. While these latter systems exhibit almost a same single ideal Maxwell behavior, solutions of bridged WM can be described as two Maxwell fluids component blends, characterized by two markedly different characteristic times, τfast and τslow, and two elastic moduli, Gfast and Gslow, with Gfast⪢Gslow. We show that the slow mode is related to the viscoelasticity of the transient network of entangled WM, and the fast mode to the network of telechelic active chains (i.e., chains that do not form loops but bridge two micelles). The dependence of the viscoelasticity with the surfactant concentration, ϕ, and the sticker-to-surfactant molar ratio, β, is discussed. In particular, we show that Gfast is proportional to the number of active chains in the material, ϕβ. Simple theoretical expectations then allow evaluation of the bridges/loops ratio for the telechelic polymers.We survey the linear viscoelasticity of a new type of transient network: bridged wormlike micelles, whose structure has been characterized recently by Ramos and Ligoure [Macromolecules 40, 1248–1251 (2007)]. This composite material is obtained by adding telechelic copolymers (water-soluble chains with hydrophobic stickers at each extremity) to a solution of entangled wormlike micelles (WM). For comparison, naked WM and WM decorated by amphiphilic copolymers are also investigated. While these latter systems exhibit almost a same single ideal Maxwell behavior, solutions of bridged WM can be described as two Maxwell fluids component blends, characterized by two markedly different characteristic times, τfast and τslow, and two elastic moduli, Gfast and Gslow, with Gfast⪢Gslow. We show that the slow mode is related to the viscoelasticity of the transient network of entangled WM, and the fast mode to the network of telechelic active chains (i.e., chains that do not form loops but bridge two micelles). The depen.
B decay shape variables and the precision determination of |V cb | and m b

We present expressions for shape variables of B decay distributions in several different mass schemes, to order $\alpha_s^2\beta_0$ and (Lambda_{QCD}/mb)^3. Such observables are sensitive to the b quark mass and matrix elements in the heavy quark effective theory, and recent measurements allow precision determinations of some of these parameters. We perform a combined fit to recent experimental results from CLEO, BABAR, and DELPHI, and discuss the theoretical uncertainties due to nonperturbative and perturbative effects. We discuss the possible discrepancy between the OPE prediction, recent BABAR results and the measured branching fraction to D and D* states. We find |Vcb| = (40.8 +- 0.9) x 10^{-3} and mb^{1S} = 4.74 +- 0.10 GeV, where the errors are dominated by experimental uncertainties.
3D global simulations of RIAFs: convergence, effects of azimuthal extent, and dynamo

We study the long-term evolution of non-radiative geometrically thick (H/R approximate to 0.5) accretion flows using 3D global ideal magnetohydrodynamic simulations and a pseudo-Newtonian gravity. We find that resolving the scale height with 42 grid points is adequate to obtain convergence with the product of quality factors similar to > > >= 300 and magnetic tilt angle theta(B) similar to 13 degrees-14 degrees. Like previous global isothermal thin disc simulations, we find stronger mean magnetic fields for the restricted azimuthal domains. Imposing periodic boundary conditions with the azimuthal extent smaller than 2 pi makes the turbulent field at low m appear as a mean field in the runs with smaller azimuthal extent. But unlike previous works, we do not find a monotonic trend in turbulence with the azimuthal extent. We conclude that the minimum azimuthal extent should be >= pi/2 to capture the flow structure, but a full 2 pi extent is necessary to study the dynamo. We find an intermittent dynamo cycle, with alpha-quenching playing an important role in the non-linear saturated state. Unlike previous local studies, we find almost similar values of kinetic and magnetic alpha-s, giving rise to an irregular distribution of dynamo-alpha. The effects of dynamical quenching are shown explicitly for the first time in global simulations of accretion flows.
A Concordance Picture of FRB 121102 as a Flaring Magnetar Embedded in a Magnetized Ion–Electron Wind Nebula

The fast radio burst FRB 121102 has repeated multiple times, enabling the identification of its host galaxy and of a spatially coincident, compact, steady (“persistent”) radio synchrotron source. It was proposed that FRB 121102 is powered by a young flaring magnetar, embedded within a decades-old supernova remnant. Using a time-dependent one-zone model, we show that a single expanding magnetized electron–ion nebula (created by the same outbursts likely responsible for the fast radio bursts) can explain all of the basic properties of the persistent source (size, flux, self-absorption constraints) and the large but decreasing rotation measure (RM) of the bursts. The persistent emission is powered by relativistic thermal electrons heated at the termination shock of the magnetar wind, while the RM originates from non-relativistic electrons injected earlier in the nebula’s evolution and cooled through expansion and radiative losses. The model contains few free parameters, which are tightly constrained by observations: the total energy injected into the nebula over its history, ∼1050−1051 erg, agrees with the magnetic energy of a millisecond magnetar; the baryon loading of the magnetar outflow (driven by intermittent flares) is close to the neutron star escape speed; the predicted source age ∼10–40 yr is consistent with other constraints on the nebula size. For an energy input rate following the onset of magnetar activity, we predict secular decay of the RM and persistent source flux, which approximately follow RM ∝ t−(6+α)/2 and , respectively.
Detailed background dynamics and trans-planckian effects in loop quantum cosmology

Cosmology appears as the most promising way to test and constrain quantum gravity theories. Loop quantum gravity is among the most advanced attempts to perform a non-perturbative quantization of general relativity. Its cosmological counterpart, loop quantum cosmology, has clear predictions both for the cosmological background and for the perturbations. In particular, the initial Big Bang singularity is replaced by a bounce due to quantum geometry effects. In this proceeding I will focus on new results obtained in loop quantum cosmology: i) the prediction of the duration of inflation as a function of all the unknown parameters of the model and ii) new primordial power spectra obtained with modified dispersion relations accounting for trans-planckian effects.
Precision Counting of Small Black Holes

It has recently been proposed that a class of supersymmetric higher-derivative interactions in = 2 supergravity may encapsulate an infinite number of finite size corrections to the microscopic entropy of certain supersymmetric black holes. If this proposal is correct, it allows one to probe the string theory description of black-hole micro-states to far greater accuracy than has been possible before. We test this proposal for ``small'' black holes whose microscopic degeneracies can be computed exactly by counting the corresponding perturbative BPS states. We also study the ``black hole partition sum'' using general properties of of BPS degeneracies. This complements and extends our earlier work in [1].
Determination of the characteristic polarization states of the target scattering matrix [S(AB)] for the coherent, monostatic, and reciprocal propagation space

A problem originating in radar polarimetry is considered for which the radar target is to be characterized by its coherent polarization state properties, given complete coherent backscattering scattering matrix data sets at one frequency and for one target aspect angle. For the monostatic reciprocal case, it is shown that there exist in total five pairs of characteristic polarization states. These include the orthogonal cross-polarization null and copolarization maximum state pairs and the orthogonal cross polarization maximum state pairs, as well as a newly identified pair, the orthogonal cross-polarization saddle point extrema which are normal to the plane spanned by the other four pairs. With this complete and unique mathematical description of Huynen's polarization fork concept, it is now possible to study the polarimetric radar target optimization problem more rigorously.
Robust pole placement for second-order linear systems using velocity-plus-acceleration feedback

This paper considers the robust pole assignment problem using combined velocity and acceleration feedbacks for matrix second-order linear systems. The necessary and sufficient conditions which ensure solvability are derived. Based on recently developed parametric solution to the eigenstructure assignment problem by velocity-plus-acceleration feedback, a new technique is described to perform robust pole placement for second-order systems. The available degrees-of-freedom offered by the velocity-plus-acceleration feedback in selecting the associated eigenvectors are utilised to improve robustness of the closed-loop system. The main advantage of the described approach is that the problem is tackled in the second-order form without transformation into the first-order form. Finally, several examples are introduced to demonstrate the effectiveness of the proposed approach.
Design of a high power synchrotron radiation absorber for HERA

In the framework of the HERA Luminosity Upgrade Project it is foreseen to move the final focus quadrupole magnets of the proton machine 16 m closer to the interaction region. As the electrons must not be affected by these magnets, the beam pipes for electrons and protons have to be well separated at these magnets. This implies rather sharp bends with bending radii down to 360 m for the electron orbit in the interaction region. At an electron energy of 30 GeV and a beam current of 58 mA these bends cause a high level of synchrotron radiation. The synchrotron radiation will be guided through the interaction region and will be absorbed far downstream at low power densities. However, it is unavoidable to stop parts of the synchrotron radiation beam at high linear power densities of up to 2 kW/cm rather close to the interaction point where the electron and proton vacuum systems are separated. In order to protect the proton final focus magnet and the septum beam pipe from this synchrotron radiation, a high power synchrotron radiation absorber was designed. This absorber not only has to withstand the heat load of the synchrotron radiation, but it also has to be designed to minimize the backward scattering of the radiation, because these scattered photons might hit sensitive detector components in the interaction region. This paper will first give an overview of the geometry of the interaction region with special emphasis on the synchrotron radiation. Then the geometrical and thermal requirements for the high power absorber will be described and finally the layout of the absorber will be presented.