ShantanuT01/DACTYL-Pretraining huggingface dataset:
Inverse Compton scattering dominates the high energy part of the spectra of neutron star (NS) low mass X-ray binaries (LMXBs). It has been proposed that inverse Compton scattering also drives the radiative properties of kilohertz quasi periodic oscillations (kHz QPOs). In this work, we construct a model that predicts the energy dependence of the rms amplitude and time lag of the kHz QPOs. Using this model, we fit the rms amplitude and time lag energy spectra of the lower kHz QPO in the NS LMXB 4U 1636-53 over 11 frequency intervals of the QPO and report three important findings: (i) A medium that extends 1-8 km above the NS surface is required to fit the data; this medium can be sustained by the balance between gravity and radiation pressure, without forcing any equilibrium condition. (ii) We predict a time delay between the oscillating NS temperature, due to feedback, and the oscillating electron temperature of the medium which, with the help of phase resolved spectroscopy, can be used as a probe of the geometry and the feedback mechanism. (iii) We show that the observed variability as a function of QPO frequency is mainly driven by the oscillating electron temperature of the medium. This provides strong evidence that the Comptonising medium in LMXBs significantly affects, if not completely drives, the radiative properties of the lower kHz QPOs regardless of the nature of the dynamical mechanism that produces the QPO frequencies.
A conjecture of Thomassen from 1982 states that for every k there is an f(k) so that every strongly f(k)-connected tournament contains k edge-disjoint Hamilton cycles. A classical theorem of Camion, that every strongly connected tournament contains a Hamilton cycle, implies that f(1)=1. So far, even the existence of f(2) was open. In this paper, we prove Thomassen's conjecture by showing that f(k)=O(k^2*log^2(k)). This is best possible up to the logarithmic factor. As a tool, we show that every strongly 10^4*k*log(k)-connected tournament is k-linked (which improves a previous exponential bound). The proof of the latter is based on a fundamental result of Ajtai, Koml\'os and Szemer\'edi on asymptotically optimal sorting networks.
The electrical field gradient (EFG), measured e.g. in perturbed angular correlation (PAC) experiments, gives particularly useful information about the interaction of probe atoms like 111In / 111Cd with other defects. The interpretation of the EFG is, however, a difficult task. This paper aims at understanding the interaction of Cd impurities with vacancies and interstitials in Si and Ge, which represents a controversial issue. We apply two complementary ab initio methods in the framework of density functional theory (DFT), (i) the all electron Korringa-Kohn-Rostoker (KKR) Greenfunction method and (ii) the Pseudopotential-Plane-Wave (PPW) method, to search for the correct local geometry. Surprisingly we find that both in Si and Ge the substitutional Cd-vacancy complex is unstable and relaxes to a split-vacancy complex with the Cd on the bond-center site. This complex has a very small EFG, allowing a unique assignment of the small measured EFGs of 54MHz in Ge and 28MHz in Si. Also, for the Cd-selfinterstitial complex we obtain a highly symmetrical split configuration with large EFGs, being in reasonable agreement with experiments.
High-resolution spectroscopic time series of rapidly oscillating Ap stars show evidence for a co-existence of standing and running waves in their atmospheric layers. With the purpose of understanding these observations we have carried out a theoretical analysis of the pulsations in the outermost layers of these stars, starting from the simplest possible model that still retains all important physical ingredients. In our analysis we considered an isothermal atmosphere in a plane-parallel approximation. Moreover we assumed that in the region considered the magnetic pressure is much larger than the gas pressure and, consequently, that the magnetoacoustic wave has decoupled into its acoustic and magnetic components. Using the analytical solutions for the velocity components appropriate to this model we estimate the velocity component parallel to the line of sight averaged over the visible stellar disk. Fitting the latter to a function of the form Acos($\sigma$t+phase), with $\sigma$ the dimensionless oscillation frequency and t the dimensionless time, we derive the amplitude A and the phase for our model as function of height in the atmosphere.
The conservative dynamics of two point masses given in harmonic coordinates up to the third post-Newtonian (3pN) order is treated within the framework of constrained canonical dynamics. A representation of the approximate Poincar\'e algebra is constructed with the aid of Dirac brackets. Uniqueness of the generators of the Poincar\'e group resp. the integrals of motion is achieved by imposing their action on the point mass coordinates to be identical with that of the usual infinitesimal Poincar\'e transformations. The second post-Coulombian approximation to the dynamics of two point charges as predicted by Feynman-Wheeler electrodynamics in Lorentz gauge is treated similarly.
To some extent, all Galactic binary systems hosting a compact object are potential `microquasars', so much as all galactic nuclei may have been quasars, once upon a time. The necessary ingredients for a compact object of stellar mass to qualify as a microquasar seem to be: accretion, rotation and magnetic field. The presence of a black hole may help, but is not strictly required, since neutron star X-ray binaries and dwarf novae can be powerful jet sources as well. The above issues are broadly discussed throughout this Chapter, with a a rather trivial question in mind: why do we care? In other words: are jets a negligible phenomenon in terms of accretion power, or do they contribute significantly to dissipating gravitational potential energy? How do they influence their surroundings? The latter point is especially relevant in a broader context, as there is mounting evidence that outflows powered by super-massive black holes in external galaxies may play a crucial role in regulating the evolution of cosmic structures. Microquasars can also be thought of as a form of quasars for the impatient: what makes them appealing, despite their low number statistics with respect to quasars, are the fast variability time-scales. In the first approximation, the physics of the jet-accretion coupling in the innermost regions should be set by the mass/size of the accretor: stellar mass objects vary on 10^5-10^8 times shorter time-scales, making it possible to study variable accretion modes and related ejection phenomena over average Ph.D. time-scales. [Abridged]
We solve a Langevin equation, first studied by de Gennes, in which there is a solid-solid or dry friction force acting on a Brownian particle in addition to the viscous friction usually considered in the study of Brownian motion. We obtain both the time-dependent propagator of this equation and the velocity correlation function by solving the associated time-dependent Fokker-Planck equation. Exact results are found for the case where only dry friction acts on the particle. For the case where both dry and viscous friction forces are present, series representations of the propagator and correlation function are obtained in terms of parabolic cylinder functions. Similar series representations are also obtained for the case where an external constant force is added to the Langevin equation.
The eigenvalues of a pure quartic oscillator are computed, applying a canonical operator formulation, generalized from the harmonic oscillator. Solving a 10x10 secular equation produces eigenvalues in agreement, to at least 4 significant figures, with accurate computations given in the literature.
The aim of this work is to investigate and characterise particle behaviour in an (observationally-driven) 3D MHD model of the solar atmosphere above a slowly evolving, non-flaring active region. We use a relativistic guiding-centre particle code to investigate the behaviour of selected particle orbits, distributed throughout a single snapshot of the 3D MHD simulation. Two distinct particle acceleration behaviours are recovered, which affect both electrons and protons: (i) direct acceleration along field lines and (ii) tangential drifting of guiding centres with respect to local magnetic field. However, up to 40\% of all particles actually experience a form of (high energy) particle trap, because of changes in the direction of the electric field and unrelated to the strength of the magnetic field; such particles are included in the first category. Additionally, category (i) electron and proton orbits undergo surprisingly strong acceleration to non-thermal energies ($\lesssim42$MeV), because of the strength and extent of super-Dreicer electric fields created by the MHD simulation. Reducing the electric field strength of the MHD model does not significantly affect the efficiency of the (electric field-based) trapping mechanism, but does reduce the peak energies gained by orbits. We discuss the implications for future experiments, which aim to simulate non-flaring active region heating and reconnection.
Let $A$ be an additive basis. We call ``essential subset'' of $A$ any finite subset $P$ of $A$ such that $A \setminus P$ is not an additive basis and that $P$ is minimal (for the inclusion order) to have this property. A recent theorem due to B. Deschamps and the author states that any additive basis has only finitely many essential subsets (see ``Essentialit\'e dans les bases additives, J. Number Theory, 123 (2007), p. 170-192''). The aim of this note is to give a simple proof of this theorem.
We present, for the first time, a statistical study of [N II] 205 mciron line emission for a large sample of local luminous infrared galaxies using Herschel Spectral and Photometric Imaging Receiver Fourier Transform Spectrometer (SPIRE FTS) data. For our sample of galaxies, we investigate the correlation between the [N II] luminosity (LNII) and the total infrared luminosity (LIR), as well as the dependence of LNII/LIR ratio on LIR, far infrared colors (IRAS $f_{60}/f_{100}$) and the [O III] 88 micron to [N II] luminosity ratio. We find that LNII correlates almost linearly with LIR for non AGN galaxies (all having $L_{IR} < 10^{12} L_solar$) in our sample, which implies that LNII can serve as a SFR tracer which is particularly useful for high redshift galaxies which will be observed with forthcoming submm spectroscopic facilities such as the Atacama Large Millimeter/submillimeter Array. Our analysis shows that the deviation from the mean LNII-LIR relation correlates with tracers of the ionization parameter, which suggests the scatter in this relation is mainly due to the variations in the hardness, and/or ionization parameter, of the ambient galactic UV field among the sources in our sample.
[abridged] We determine the relationship between turbulence energy and gas density variance for 15 molecular clouds in the Solar neighbourhood. We use the linewidths of the CO molecule as the probe of the turbulence energy (sonic Mach number, $\cal{M}_\mathrm{s}$) and three-dimensional models to reconstruct the density probability distribution function ($\rho$-PDF) of the clouds, derived using near-infrared extinction and Herschel dust emission data, as the probe of the density variance ($\sigma_\mathrm{s}$). We find no significant correlation between $\cal{M}_\mathrm{s}$ and $\sigma_\mathrm{s}$ among the studied clouds, however, we also cannot rule out a weak correlation. In the context of turbulence-dominated gas, the range of the $\cal{M}_\mathrm{s}$ and $\sigma_\mathrm{s}$ values corresponds with the model predictions. The data cannot constrain whether or not the turbulence driving parameter, $b$, and/or thermal-to-magnetic pressure ratio, $\beta$, vary among the sample clouds. Most clouds are not in agreement with field strengths stronger than given by $\beta \lesssim 0.05$. A model with $b^2 \beta / (\beta+1) = 0.30 \pm 0.06$ provides an adequate fit to the cloud sample as a whole. When considering the average behaviour of the sample, we can rule out three regimes: (i) strong compression combined with a weak magnetic field ($b \gtrsim 0.7$ and $\beta \gtrsim 3$), (ii) weak compression ($b \lesssim 0.35$), and (iii) strong magnetic field ($\beta \lesssim 0.1$). Including independent magnetic field strength estimates to the analysis, the data rule out solenoidal driving ($b < 0.4$) for the majority of the Solar neighbourhood clouds. However, most clouds have $b$ parameters larger than unity, which indicates a discrepancy with the turbulence-dominated picture; we discuss the possible reasons for this.
Visible-infrared person re-identification (VI-ReID) is a challenging cross-modality pedestrian retrieval problem. Due to the large intra-class variations and cross-modality discrepancy with large amount of sample noise, it is difficult to learn discriminative part features. Existing VI-ReID methods instead tend to learn global representations, which have limited discriminability and weak robustness to noisy images. In this paper, we propose a novel dynamic dual-attentive aggregation (DDAG) learning method by mining both intra-modality part-level and cross-modality graph-level contextual cues for VI-ReID. We propose an intra-modality weighted-part attention module to extract discriminative part-aggregated features, by imposing the domain knowledge on the part relationship mining. To enhance robustness against noisy samples, we introduce cross-modality graph structured attention to reinforce the representation with the contextual relations across the two modalities. We also develop a parameter-free dynamic dual aggregation learning strategy to adaptively integrate the two components in a progressive joint training manner. Extensive experiments demonstrate that DDAG outperforms the state-of-the-art methods under various settings.
M1 properties, comprising magnetic moments and radiative capture of thermal neutron observables, are studied in two- and three-nucleon systems. We utilize meson exchange current derived up to N$^3$LO using heavy baryon chiral perturbation theory a la Weinberg. Calculations have been performed for several qualitatively different realistic nuclear Hamiltonians, which permits us to analyze model dependence of our results. Our results are found to be strongly correlated with the effective range parameters such as binding energies and the scattering lengths. Taking into account such correlation, the results are in good agreement with the experimental data with small model-dependence.
Rotation moment invariants have been of great interest in image processing and pattern recognition. This paper presents a novel kind of rotation moment invariants based on the Slepian functions, which were originally introduced in the method of separation of variables for Helmholtz equations. They were first proposed for time series by Slepian and his coworkers in the 1960s. Recent studies have shown that these functions have an good performance in local approximation compared to other approximation basis. Motivated by the good approximation performance, we construct the Slepian-based moments and derive the rotation invariant. We not only theoretically prove the invariance, but also discuss the experiments on real data. The proposed rotation invariants are robust to noise and yield decent performance in facial expression classification.
We present a generic algorithm for generating Gaussian random initial conditions for cosmological simulations on periodic rectangular lattices. We show that imposing periodic boundary conditions on the real-space correlator and choosing initial conditions by convolving a white noise random field results in a significantly smaller error than the traditional procedure of using the power spectrum. This convolution picture produces exact correlation functions out to separations of L/2, where L is the box size, which is the maximum theoretically allowed. This method also produces tophat sphere fluctuations which are exact at radii $ R \le L/4 $. It is equivalent to windowing the power spectrum with the simulation volume before discretizing, thus bypassing sparse sampling problems. The mean density perturbation in the volume is no longer constrained to be zero, allowing one to assemble a large simulation using a series of smaller ones. This is especially important for simulations of Lyman-$\alpha$ systems where small boxes with steep power spectra are routinely used.   We also present an extension of this procedure which generates exact initial conditions for hierarchical grids at negligible cost.
Phase separation and criticality are analyzed in $z$:1 charge-asymmetric ionic fluids of equisized hard spheres by generalizing the Debye-H\"{u}ckel approach combined with ionic association, cluster solvation by charged ions, and hard-core interactions, following lines developed by Fisher and Levin (1993, 1996) for the 1:1 case (i.e., the restricted primitive model). Explicit analytical calculations for 2:1 and 3:1 systems account for ionic association into dimers, trimers, and tetramers and subsequent multipolar cluster solvation. The reduced critical temperatures, $T_c^*$ (normalized by $z$), \textit{decrease} with charge asymmetry, while the critical densities \textit{increase} rapidly with $z$. The results compare favorably with simulations and represent a distinct improvement over all current theories such as the MSA, SPB, etc. For $z$$\ne$1, the interphase Galvani (or absolute electrostatic) potential difference, $\Delta \phi(T)$, between coexisting liquid and vapor phases is calculated and found to vanish as $|T-T_c|^\beta$ when $T\to T_c-$ with, since our approximations are classical, $\beta={1/2}$. Above $T_c$, the compressibility maxima and so-called $k$-inflection loci (which aid the fast and accurate determination of the critical parameters) are found to exhibit a strong $z$-dependence.
Ultra-luminous quasars ($M_{1450} \leq -29$) provide us with a rare view into the nature of the most massive and most rapidly accreting supermassive black holes (SMBHs). Following the discovery of two of these extreme sources, J0341${+}$1720 ($M_{1450}=-29.56$, $z=3.71$) and J2125${-}$1719 ($M_{1450}=-29.39$, $z=3.90$), in the Extremely Luminous Quasar Survey (ELQS) and its extension to the Pan-STARRS\,1 footprint (PS-ELQS), we herein present an analysis of their rest-frame UV to optical spectroscopy. Both quasars harbor very massive SMBHs with $M_{\rm{BH}}=6.73_{-0.83}^{+0.75}\times10^{9}\,M_{\odot}$ and $M_{\rm{BH}}=5.45_{-0.55}^{+0.60}\times10^{9}\,M_{\odot}$, respectively, showing evidence of accretion above the Eddington limit ($L_{\rm{bol}}/L_{\rm{Edd}}=2.74_{-0.27}^{+0.39}$ and $L_{\rm{bol}}/L_{\rm{Edd}}=3.01_{-0.30}^{+0.34}$). NOEMA 3 millimeter observations of J0341${+}$1720 reveal a highly star-forming ($\rm{SFR}\approx1500\,M_{\odot}\,\rm{yr}^{-1}$), ultra-luminous infrared galaxy ($L_{\rm{TIR}}\approx1.0\times10^{13}\,L_{\odot}$) host, which, based on an estimate of its dynamical mass, is only ${\sim}30$ times more massive than the SMBH it harbors at its center. As examples of luminous super-Eddington accretion, these two quasars provide support for theories, which explain the existence of billion solar mass SMBHs ${\sim}700$ million years after the Big Bang by moderate super-Eddington growth from standard SMBH seeds.
A new three parameter formula is proposed for ground-state bands in even-even soft rotors or called transitional nuclei. The new formula blends those of very soft nuclei and well deformed nuclei. Especially, it is found in fact that the formula proposed by P. von Brentano et al. can be derived from our formula if some approximations are adopted and it can be explained why in their work the energy-dependent term beta*E can be dropped. Compared to their formula it can be resulted in that the range of validity of our formula will be much broader than theirs.
We discuss the tests of general Three Gauge Boson Vertices (TGV) through bosonic pair production at present and future hadron colliders. All bosonic final states are reviewed via the tree level quark-antiquark annihilation sub-process. The full analytic expressions of the helicity amplitudes and cross-sections are given. These expressions should be useful in any attempt to disentangle the effects of the most general non standard $WWV (V=\gamma,Z)$ vertices including 14 free parameters. We investigate the sensitivity of the invariant mass and transverse momentum distributions to the full set of anomalous couplings including final state polarization structures. We particularly consider these features at the projected CERN Large Hadron Collider (LHC) energy scale.
We consider the high frequency Helmholtz equation with a variable refraction index $n^2(x)$ ($x \in \R^d$), supplemented with a given high frequency source term supported near the origin $x=0$. A small absorption parameter $\alpha_{\varepsilon}>0$ is added, which somehow prescribes a radiation condition at infinity for the considered Helmholtz equation. The semi-classical parameter is $\varepsilon>0$. We let $\eps$ and $\a_\eps$ go to zero {\em simultaneaously}. We study the question whether the indirectly prescribed radiation condition at infinity is satisfied {\em uniformly} along the asymptotic process $\eps \to 0$, or, in other words, whether the conveniently rescaled solution to the considered equation goes to the {\em outgoing} solution to the natural limiting Helmholtz equation. This question has been previously studied by the first autor. It is proved that the radiation condition is indeed satisfied uniformly in $\eps$, provided the refraction index satisfies a specific {\em non-refocusing condition}, a condition that is first pointed out in this reference. The non-refocusing condition requires, in essence, that the rays of geometric optics naturally associated with the high-frequency Helmholtz operator, and that are sent from the origin $x=0$ at time $t=0$, should not refocus at some later time $t>0$ near the origin again. In the present text we show the {\em optimality} of the above mentionned non-refocusing condition, in the following sense. We exhibit a refraction index which {\em does} refocus the rays of geometric optics sent from the origin near the origin again, and, on the other hand, we completely compute the asymptotic behaviour of the solution to the associated Helmholtz equation: we show that the limiting solution {\em does not} satisfy the natural radiation condition at infinity. More precisely, we show that the limiting solution is a {\em perturbation} of the outgoing solution to the natural limiting Helmholtz equation, and that the perturbing term explicitly involves the contribution of the rays radiated from the origin which go back to the origin. This term is also conveniently modulated by a phase factor, which turns out to be the action along the above rays of the hamiltonian associated with the semiclassical Helmholtz equation.
We present the discovery of IGR J18245-2452, the first millisecond pulsar observed to swing between a rotation-powered, radio pulsar state, and an accretion-powered X-ray pulsar state (Papitto et al. 2013, Nature, 501, 517). This transitional source represents the most convincing proof of the evolutionary link shared by accreting neutron stars in low mass X-ray binaries, and radio millisecond pulsars. It demonstrates that swings between these two states take place on the same time-scales of luminosity variations of X-ray transients, and are therefore most easily interpreted in terms of changes in the rate of mass in-flow.   While accreting mass, the X-ray emission of IGR J18245-2452 varies dramatically on time-scales ranging from a second to a few hours. We interpret a state characterised by a lower flux and pulsed fraction, and by sudden increases of the hardness of the X-ray emission, in terms of the onset of a magnetospheric centrifugal inhibition of the accretion flow. Prospects of finding new members of the newly established class of transitional pulsars are also briefly discussed.