Miracle-dz/UniFAR-FTUs huggingface dataset:
Thermo-Statistics or Topology of the Microcanonical Entropy Surface

Boltzmann’s principle S ( E, N, V · · · ) = ln W ( E,N, V · · · ) allows the interpretation of Statistical Mechanics of a closed system as Pseudo-Riemannian geometry in the space of the conserved parameters E, N, V · · · (the conserved mechanical parameters in the language of Ruppeiner [1]) without invoking the thermodynamic limit. The topology is controlled by the curvature of S ( E, N, V · · · ). The most interesting region is the region of (wrong) positive maximum curvature, the region of phase-separation. This is demonstrated among others for the equilibrium of a typical non-extensive system, a self-gravitating and rotating cloud in a spherical container at various energies and angular-momenta. A rich variety of realistic conﬁgurations, as single stars, multi-star systems, rings and ﬁnally gas, are obtained as equilibrium microcanonical phases. The global phase diagram, the topology of the curvature, as function of energy and angular-momentum is presented. No exotic form of thermodynamics like Tsallis [2,3] non-extensive one is necessary. It is further shown that a ﬁnite (even mesoscopic) system approaches equilibrium with a change of its entropy ∆S ≥ 0 (Second Law) even when its Poincarr´e recurrence time is not large. Pseudo-Riemannian geometry.
Dwarf Cepheids in the Carina Dwarf Spheroidal Galaxy

We have discovered 20 dwarf Cepheids (DCs) in the Carina dwarf spheroidal galaxy from an analysis of individual CCD images obtained for a deep photometric study of the system. These short-period pulsating variable stars are by far the most distant (∼100 kpc) and faintest (V ∼ 23.0) DCs known. The Carina DCs obey a well-defined period-luminosity relation, allowing us to readily distinguish between overtone and fundamental pulsators in nearly every case. Unlike RR Lyrae stars, the pulsation mode turns out to be uncorrelated with light-curve shape, and the overtone pulsators do not tend toward shorter periods compared with the fundamental pulsators. Using the period-luminosity relations from Nemec, Nemec, & Lutz and McNamara, we derive (m - M)0 = 20.06 ± 0.12, for E(B - V) = 0.025 and [Fe/H] = -2.0, in good agreement with recent, independent estimates of the distance/reddening of Carina. The error reflects the uncertainties in the DC distance scale, and in the metallicity and reddening of Carina. The frequency of DCs among upper–main-sequence stars in Carina is approximately 3%. The ratio of dwarf Cepheids to RR Lyrae stars in Carina is 0.13 ± 0.10, though this result is highly sensitive to the star formation history of Carina and the evolution of the horizontal branch. We discuss how DCs may be useful to search effectively for substructure in the Galactic halo out to Galactocentric distances of ≲100 kpc.
Internal gas models and central black hole in 47 Tucanae using millisecond pulsars

Despite considerations of mass loss from stellar evolution suggesting otherwise, the content of gas in globular clusters seems poor and hence its measurement very elusive. One way of constraining the presence of ionized gas in a globular cluster is through its dispersive effects on the radiation of the millisecond pulsars included in the cluster. This effect led Freire et al. in 2001 to the first detection of any kind of gas in a globular cluster in the case of 47 Tucanae. By exploiting the results of 12 additional years of timing, as well as the observation of new millisecond pulsars in 47 Tucanae, we revisited this measurement: we first used the entire set of available timing parameters in order to measure the dynamical properties of the cluster and the three-dimensional position of the pulsars. Then we applied and tested various gas distribution models: assuming a constant gas density, we confirmed the detection of ionized gas with a number density of $n= 0.23\pm 0.05$ cm$^{-3}$, larger than the previous determination (at 2$\sigma$ uncertainty). Models predicting a decreasing density or following the stellar distribution density are highly disfavoured. We are also able to investigate the presence of an intermediate mass black hole in the centre of the cluster, showing that is not required by the available data, with an upper limit for the mass at $\sim 4000$ M$_{\odot}$.
Coexistence of multiple nonlinear states in a tristable passive kerr resonator

Pattern formation in optical devices known as passive Kerr resonators has been studied for decades, but recent theoretical work has suggested the existence of entirely new dynamics when operated in the highly nonlinear regime. New experiments confirm these predictions, which could lead to innovative new sources of laser-like light and provide new insight into nonlinear dynamics and pattern formation.
Thermionic refrigerators with non-Richardson current

Most models of solid-state thermionic devices assume that all electrons with energy in the direction of transport greater than the barrier height are transmitted and utilize the Richardson equation. Here we consider a number of thermionic systems where the electron energy spectrum differs from the Richardson model. The electron energy spectra for maximum refrigeration coefficient of performance and maximum power are presented. We then consider multilayer solid-state nanostructures with currents not given by the Richardson equation and discuss the optimization of their energy spectrum. Nanometre gap vacuum thermionic refrigerators are also treated, where significant current is provided by below the barrier tunnelling. Finally, equations are developed for devices that select electrons for emission according to their total momentum, rather than simply the value in the direction of transport as is the case with conventional devices.
Gravitational Lens Statistics for Generalized NFW Profiles: Parameter Degeneracy and Implications for Self-Interacting Cold Dark Matter

Strong lensing is a powerful probe of the distribution of matter in the cores of clusters of galaxies. Recent studies suggest that the cold dark matter model predicts cores that are denser than those observed in galaxies, groups, and clusters. One possible resolution of the discrepancy is that the dark matter has strong interactions (SIDM), which leads to lower central densities. A generalized form of the Navarro, Frenk, & White profile (Zhao profile) can be used to describe these halos. In this paper we examine gravitational lensing statistics for this class of model. The optical depth to multiple imaging is a very sensitive function of the profile parameters in the range of interest for SIDM halos around clusters of galaxies. Less concentrated profiles, which result from larger self-interaction cross sections, can produce many fewer lensed pairs. Furthermore, profiles that result in a small optical depth exhibit reduced typical splittings, but produce multiple images that are more highly magnified. However, the resulting increased magnification bias does not alter our conclusions. We find that lensing statistics based on profile parameters obtained from fits out to the virial radius are dependent on the minimization scheme adopted, and may be seriously in error. However, profile fits weighted toward the core region have parameter degeneracies that are approximately equivalent to those for strong-lensing cross sections. Lensing statistics provide a powerful test for SIDM. More realistic and observationally oriented calculations remain to be done; however, larger self-interaction cross sections may well be ruled out by the very existence of strong lenses on galaxy cluster scales. The inclusion of centrally dominant cluster galaxies should boost the cross section to multiple imaging. However, our preliminary calculations suggest that the additional multiple imaging rate is small with respect to the differences in multiple imaging rate for different halo profiles. In future statistical studies, it will be important to properly account for the scatter among halo profiles, since the optical depth to multiple imaging is dominated by the most concentrated members of a cluster population.
Resonant Cyclotron Radiation Transfer Model Fits to Spectra from Gamma-Ray Burst GRB 870303

We demonstrate that models of resonant cyclotron radiation transfer in a strong field (i.e., cyclotron scattering) can account for spectral lines seen at two epochs, denoted S1 and S2, in the Ginga data for GRB 870303. S1, which extends 4 s, exhibits one line at ≈20 keV, while S2, which extends 9 s, exhibits harmonically spaced lines at ≈20 and 40 keV. The midpoints of S1 and S2 are separated by 22.5 s. Using a generalized version of the Monte Carlo code of Wang et al., we model line formation by injecting continuum photons into a static plane-parallel slab of electrons threaded by a strong neutron star magnetic field (~1012 G) that may be oriented at an arbitrary angle relative to the slab normal. We examine two source geometries, which we denote "1-0" and "1-1," with the numbers representing the relative electron column densities above and below the continuum photon source plane. The 1-0 geometry may represent, e.g., a line formation region levitating above the surface of the neutron star, or possibly a plasma-filled flux tube illuminated from below. The 1-1 geometry, on the other hand, corresponds to line formation in a semi-infinite atmosphere at the surface of a neutron star. We apply rigorous statistical inference to compare azimuthally symmetric models, i.e., models in which the magnetic field is parallel to the slab normal, with models having more general magnetic field orientations. If the bursting source has a simple dipole field, these two model classes represent line formation at the magnetic pole, or elsewhere on the stellar surface. We find that the data of S1 and S2, considered individually, are consistent with both geometries, and with all magnetic field orientations, with the exception that the S1 data clearly favors line formation away from a polar cap in the 1-1 geometry, with the best-fit model placing the line-forming region at the magnetic equator. Within both geometries, fits to the combined (S1 + S2) data marginally favor models that feature equatorial line formation, and in which the observer's orientation with respect to the slab changes between the two epochs. We interpret this change as being due to neutron star rotation, and we place limits on the rotation period.
Hierarchical Modeling of Multifunctional Novel Carbon Nanotube Reinforced Hybrid Composites for Next Generation Polymeric Composites

This article provides an overview of the modeling of the effective thermomechanical properties of the multifunctional carbon nanotube (CNT) reinforced hybrid composites for advanced structural applications. The novel constructional feature of such multifunctional CNT-reinforced hybrid composite is that CNTs are radially grown on the circumferential surfaces of the carbon fiber reinforcements. Several micromechanical models have been developed to predict the effective thermomechanical properties of these multifunctional CNT-reinforced hybrid composites. The waviness of CNTs is intrinsic to many manufacturing processes and influences the thermomechanical behavior of CNT-reinforced composites. An endeavor has also been made to investigate the effect of wavy CNTs on the thermomechanical properties of the multifunctional CNT-reinforced hybrid composites. Radially aligned CNTs grown on the circumferential surfaces of the carbon fibers assure that the CNT-reinforced hybrid composites are truly multifunctional and may be a promising advanced next generation composite for structural applications.
Broadband Plasma Waves in the Boundary Layers

Boundary layers are commonly encountered in space and astrophysical plasmas. For example, interaction of solar wind plasma with the planets and comets produces magnetopause and cometopause boundary layers, respectively. Generally, the boundary layers are formed when plasmas with different characteristics interact with each other. The plasma sheet boundary layer in the Earth's magnetotail is formed owing to the interaction of hot dense plasma in the plasma sheet region with the rarefied plasma of the lobe region. Boundary layers are the site where energy and momentum are exchanged between two distinct plasmas. Boundary layers occurring in space plasmas can support a wide spectrum of plasma waves spanning a frequency range of a few mHz to 100 kHz and beyond. The purpose of this review is to describe the main characteristics and the possible generation mechanisms of the broadband plasma waves (with frequencies of > 1 Hz) observed in the Earth's magnetopause boundary layer, the Jovian magnetopause boundary layer, the plasma sheet boundary layer, and the Earth's polar cap boundary layer. The rapid pitch angle scattering of energetic particles via cyclotron resonant interactions with the waves can provide sufficient precipitated energy flux to the ionosphere to create the dayside aurora at Earth and a weak high-latitude auroral ring at Jupiter. In general, the broadband plasma waves may play an important part in the processes of local heating/acceleration of the boundary layer plasma. Recent exciting high time resolution results on the broadband plasma waves coming from Geotail, Polar, and FAST will be discussed.
The galaxy clustering crisis in abundance matching

Galaxy clustering on small scales is significantly under-predicted by sub-halo abundance matching (SHAM) models that populate (sub-)haloes with galaxies based on peak halo mass, $M_{\rm peak}$. SHAM models based on the peak maximum circular velocity, $V_{\rm peak}$, have had much better success. The primary reason $M_{\rm peak}$ based models fail is the relatively low abundance of satellite galaxies produced in these models compared to those based on $V_{\rm peak}$. Despite success in predicting clustering, a simple $V_{\rm peak}$ based SHAM model results in predictions for galaxy growth that are at odds with observations. We evaluate three possible remedies that could "save" mass-based SHAM: (1) SHAM models require a significant population of "orphan" galaxies as a result of artificial disruption/merging of sub-haloes in modern high resolution dark matter simulations; (2) satellites must grow significantly after their accretion; and (3) stellar mass is significantly affected by halo assembly history. No solution is entirely satisfactory. However, regardless of the particulars, we show that popular SHAM models based on $M_{\rm peak}$ cannot be complete physical models as presented. Either $V_{\rm peak}$ truly is a better predictor of stellar mass at $z\sim 0$ and it remains to be seen how the correlation between stellar mass and $V_{\rm peak}$ comes about, or SHAM models are missing vital component(s) that significantly affect galaxy clustering.
Magnetoresistance oscillations induced by high-intensity terahertz radiation

We report on observation of pronounced terahertz radiation-induced magnetoresistivity oscillations in AlGaAs/GaAs two-dimensional electron systems, the terahertz analog of the microwave induced resistivity oscillations (MIRO). Applying high-power radiation of a pulsed molecular laser we demonstrate that MIRO, so far observed at low power only, are not destroyed even at very high intensities. Experiments with radiation intensity ranging over five orders of magnitude from 0.1 to ${10}^{4}\phantom{\rule{0.16em}{0ex}}{\mathrm{W}/\mathrm{cm}}^{2}$ reveal high-power saturation of the MIRO amplitude, which is well described by an empirical fit function $I/{(1+I/{I}_{s})}^{\ensuremath{\beta}}$ with $\ensuremath{\beta}\ensuremath{\sim}1$. The saturation intensity ${I}_{s}$ is of the order of tens of watts per square centimeter and increases by a factor of 6 by increasing the radiation frequency from 0.6 to 1.1 THz. The results are discussed in terms of microscopic mechanisms of MIRO and compared to nonlinear effects observed earlier at significantly lower excitation frequencies.
Energy nonequipartition in systems of inelastic, rough spheres

We calculate and verify with simulations the ratio between the average translational and rotational energies of systems with rough, inelastic particles, either forced or freely cooling. The ratio shows a nonequipartition of energy. In stationary flows, this ratio depends mainly on the particle roughness, but in nonstationary flows, such as freely cooling granular media, it also depends strongly on the normal dissipation. The approach presented here unifies and simplifies different results obtained by more elaborate kinetic theories. We observe that the boundary induced energy flux plays an important role.
Minimal model for extragalactic cosmic rays and neutrinos

We aim to explain in a unified way the experimental data on ultrahigh energy cosmic rays (UHECR) and neutrinos, using a single source class and obeying limits on the extragalactic diffuse gamma-ray background (EGRB). If UHECRs only interact hadronically with gas around their sources, the resulting diffuse CR flux can be matched well to the observed one, providing at the same time large neutrino fluxes. However, air showers in the Earth's atmosphere induced by UHECRs with energies $E>3\times 10^{18}$ eV would reach in such a case their maxima too high. Therefore additional photo-hadronic interactions of UEHCRs close to the accelerator have to be present, in order to modify the nuclear composition of CRs in a relatively narrow energy interval. We include thus both photon and gas backgrounds, and combine the resulting CR spectra with the high-energy part of the Galactic CR fluxes predicted by the escape model. As result, we find a good description of experimental data on the total CR flux, the mean shower depth $X_\max$ and its width $RMS(X_\max)$ in the whole energy range above $E\simeq 10^{17}$ eV. The predicted high-energy neutrino flux matches IceCube measurements, while the contribution to the EGRB is of order 30%.
Variability of summer rainfall over tropical north Africa (1906–92): Observations and modelling

The nature and causes of seasonal (July to September (JAS)) rainfall variability over tropical north Africa are investigated using a combination of empirical and modelling approaches. Concentration is focused on three regions: the Sahel, Soudan and Guinea Coast. The variability of seasonal rainfall through the twentieth century is analysed for each region. The well known dipole of anomalies between the Sahel and Guinea Coast is evident, and new analysis reveals that this fluctuates primarily on time-scales of five years or less. Attention is then focussed on the causes of rainfall variability in each region, by examining the relationships with global sea-surface-temperature (SST) patterns; a partitioning of the data into low- and high-frequency components is found to be particularly useful. So as to attribute more convincingly the primary cause of seasonal rainfall variability to global SST forcing, a suite of general circulation model experiments are performed, aimed at simulating JAS rainfall anomalies for ten past years between 1949 and 1990. Each is forced by the observed SST patterns for the appropriate year. In almost every case, the model quite skilfully simulates the magnitude and pattern of JAS rainfall anomalies across tropical north Africa, thus strengthening the idea that global SST variations are indeed responsible for most of the variability of seasonal rainfall. The relative impact of two additional sources of variability is also investigated. First the role of internal atmospheric variability is quantified (using an ‘analysis of variance’ technique), and found to be small in all three regions. Second, and perhaps more controversially, the possible effects of land-surface-moisture feedback are explored. This is done by replacing the normal interactive soil-moisture scheme with a model-derived climatology; results suggest that in some years moisture evaporated from the land surface may play a key role, but that in general SST forcing still dominates. Finally, an assessment of the model's skill at sub-seasonal time-scales reveals that fluctuations of monthly rainfall about each year's seasonal mean (intraseasonal variations) are insensitive to SST forcing, in part due to a larger influence of internal atmospheric variations.
Homologous Confined Filament Eruptions via Magnetic Breakout

We describe magnetohydrodynamic simulations of a bipolar active region embedded in the Sun’s global background field and subjected to twisting footpoint displacements concentrated near its polarity inversion lines to produce strong magnetic shear. The dipole moments of the active region and background field are antiparallel, so that the initially potential magnetic field contains a coronal null. This configuration supports magnetic breakout eruptions in our simulations that exhibit three novel features. First, the eruptions are multiple and homologous: the flare reconnection following each eruption reforms the magnetic null, setting the stage for a subsequent episode of breakout reconnection and eruption driven by the ongoing footpoint motions. Second, the eruptions are confined; that is, their rapidly rising, moderately sheared field lines do not escape the Sun but instead come to rest in the outer corona, comprising a large coronal loop formed by reconnection during the rise phase. Third, the most strongly sheared field lines of the active region are quite flat prior to eruption, expand upward sharply during the event, and lose most of their shear through reconnection with overlying flux, while lower lying field lines survive the eruption and recover their flat configuration within a few hours. These behaviors are consistent with filament disappearance followed by reformation in place. We also find that the upward motion of the erupting sheared flux exhibits a distinct three-phase acceleration profile. All of these features of our simulations—homology, confinement, reformation, and multiphase acceleration—are well established aspects of solar eruptions.
Neutrino oscillations in the early universe: A Real time formulation

Neutrino oscillations in the early universe prior to the epoch of primordial nucleosynthesis is studied by implementing real-time nonequilibrium field theory methods. We focus on two flavors of Dirac neutrinos, however, the formulation is general. We obtain the equations of motion for neutrino wave packets of either chirality and helicity in the plasma allowing for CP asymmetry. Contributions nonlocal in space-time to the self-energy dominate over the asymmetry for T > or approx. 3-5 MeV if the lepton and neutrino asymmetries are of the same order as the baryon asymmetry. We find a new contribution which cannot be interpreted as the usual effective potential. The mixing angles and dispersion relations in the medium depend on helicity. We find that resonant transitions are possible in the temperature range 10 < or approx. T<<100 MeV. Near a resonance in the mixing angle, the oscillation time scale in the medium as compared to the vacuum is slowed down substantially for small vacuum mixing angle. The time scale of oscillations speeds up for off-resonance high energy neutrinos for which the mixing angle becomes vanishingly small. The equations of motion reduce to the familiar oscillation formulae for negative helicity ultrarelativistic neutrinos, but include consistently bothmore » the mixing angle and the oscillation frequencies in the medium. These equations of motion also allow to study the dynamics of right handed as well as positive helicity neutrinos. « less