ShantanuT01/DACTYL-Pretraining huggingface dataset:
Recent inelastic neutron scattering (INS) experiments of the triangular antiferromagnet Ba$_3$CoSb$_2$O$_9$ revealed strong deviations from semiclassical theories. We demonstrate that key features of the INS data are well reproduced by a parton Schwinger boson theory beyond the saddle-point approximation. The measured magnon dispersion is well reproduced by the dispersion of two-spinon bound states (poles of the emergent gauge fields propagator), while the low-energy continuum scattering is reproduced by a quasifree two-spinon continuum, suggesting that a free-spinon gas is a good initial framework to study magnetically ordered states near a quantum melting point.
I report on the APOKASC catalog, a joint effort between the Kepler Asteroseismic Science Consortium and the SDSS-III APOGEE spectroscopic survey. It will contain both seismic and spectroscopic values for stars observed by both surveys. I discuss the derivation of spectroscopic parameters and their uncertainties from the H-band spectra delivered by the APOGEE spectrograph, illustrating the sensitivity of stellar spectra to some parameters, such as Teff, and lack of sensitivity to others, such as logg.
We introduce a microscopic approach to derive all the inertial functions in the five-dimensional quadrupole collective Hamiltonian. Local normal modes are evaluated on the constrained mean field in the quasiparticle random-phase approximation in order to derive the inertial functions. The collective Hamiltonians for neutron-rich Mg isotopes are determined with use of this approach, and the shape coexistence/mixing around the N = 20 region is analyzed.
We study the problem of more general kinematics for the finite N M(atrix)-Model than the simple straight line motion that has been used before. This is supposed to be related to momentum transferring processes in the dual super-gravity description. We find a negative result for classical, perturbative processes and discuss briefly the possibility of instianton like quantum mechanical tunneling processes.
The power of asteroseismology relies on the ability to infer the stellar structure from the unambiguous frequency identification of the corresponding pulsation mode. Hence, the use of a Fourier transform is in the basis of asteroseismic studies. Nevertheless, the difficulties with the interpretation of the frequencies found in many stars lead us to reconsider whether Fourier analysis is the most appropriate technique to identify pulsation modes. We have found that the data, usually analyzed using Fourier techniques, present a non-analyticity originating from the lack of connectivity of the underlying function describing the physical phenomena. Therefore, the conditions for the Fourier series to converge are not fulfilled. In the light of these results, we examine in this talk some stellar light curves from different asteroseismology space missions (CoRoT, Kepler and SoHO) in which the interpretation of the data in terms of Fourier frequencies becomes difficult. We emphasize the necessity of a new interpretation of the stellar light curves in order to identify the correct frequencies of the pulsation modes.
Ultrarelativistic heavy ion beams carry large electromagnetic and strong absorptive fields, allowing exploration of a variety of physics. Two-photon, photon-Pomeron, and double Pomeron interactions can probe a huge variety of couplings and final states. RHIC will be the first heavy ion accelerator energetic enough to produce hadronic final states via coherent couplings. Virtual photons from the nuclear EM fields can interact in two-photon interactions, which can be exploited to study many particle spectroscopy and QCD topics. Because the photon flux scales as $Z^2$, Two-photon luminosities are large up to an energy of about \gamma\hbar c/R~ 3 GeV/c. Photon-Pomeron interactions are sensitive to how different vector mesons, including the $J/\psi$, interact with nuclear matter. $PP$ collisions rates are sensitive to the range of the Pomeron. Signals can be separated from backgrounds by using cuts on final state isolation (rapidity gaps) and $p_\perp$. We present Monte Carlo studies of different backgrounds, showing that representative signals can be extracted with good rates and signal to noise ratios.
We study the one-level density for families of L-functions associated with cubic Dirichlet characters defined over the Eisenstein field. We show that the family of $L$-functions associated with the cubic residue symbols $\chi_n$ with $n$ square-free and congruent to 1 modulo 9 satisfies the Katz-Sarnak conjecture for all test functions whose Fourier transforms are supported in $(-13/11, 13/11)$, under GRH. This is the first result extending the support outside the \emph{trivial range} $(-1, 1)$ for a family of cubic L-functions. This implies that a positive density of the L-functions associated with these characters do not vanish at the central point $s=1/2$. A key ingredient in our proof is a bound on an average of generalized cubic Gauss sums at prime arguments, whose proof is based on the work of Heath-Brown and Patterson.
We revisit the random $m$-ary search tree and study a finer profile of its node outdegrees with the purpose of exploring possibilities of data structure compression. The analysis is done via P\'olya urns. The analysis shows that the number of nodes of each individual node outdegree has a phase transition: Up to $m=26$, the number of nodes of outdegree $k$, for $k=0,1, \ldots, m$, is asymptotically normal; that behavior changes at $m = 27$. Based on the analysis, we propose a compact $m$-ary tree that offers significant space saving.
A new mechanism of electron paramagnetic resonance in spherical zinc-blende semiconductor nanocrystals, based on the extended orbital motion of electrons in the entire nanocrystal, is presented. Quantum confinement plays a crucial role in making the resonance signal observable. The mechanism remains operative in nanocrystals with uniaxially distorted shape. A theoretical model based on the proposed mechanism is in good quantitative agreement with unusual ODMR spectra observed in nearly spherical CdSe nanocrystals.
We study by numerical simulations the two-dimensional Inelastic Maxwell Model (IMM), and show how the inelasticity of collisions together with the fluctuations of the number of collisions undergone by a particle lead to energy fluctuations that decay like a power-law. These fluctuations are associated to a shrinking of the available phase space. We find the asymptotic scaling of these energy fluctuations and show how they affect the tail of the velocity distribution during long time intervals.
We present an investigation of a large sample of confirmed (N=233) and candidate (N=54) Galactic classical Be stars (mean V magnitude range of 6.4 to 12.6 mag), with the main aim of characterizing their photometric variability. Our sample stars were preselected among early-type variables using light curve morphology criteria. Spectroscopic information was gleaned from the literature, and archival and newly-acquired spectra. Photometric variability was analyzed using archival ASAS-3 time series data. To enable a comparison of results, we have largely adopted the methodology of Labadie-Bartz et al. (2017), who carried out a similar investigation based on KELT data. Complex photometric variations were established in most stars: outbursts on different time-scales (in 73$\pm$5% of stars), long-term variations (36$\pm$6%), periodic variations on intermediate time-scales (1$\pm$1%) and short-term periodic variations (6$\pm$3%). 24$\pm$6% of the outbursting stars exhibit (semi)periodic outbursts. We close the apparent void of rare outbursters reported by Labadie-Bartz et al. (2017) and show that Be stars with infrequent outbursts are not rare. While we do not find a significant difference in the percentage of stars showing outbursts among early-type, mid-type and late-type Be stars, we show that early-type Be stars exhibit much more frequent outbursts. We have measured rising and falling times for well-covered and well-defined outbursts. Nearly all outburst events are characterized by falling times that exceed the rising times. No differences were found between early-, mid- and late-type stars; a single non-linear function adequately describes the ratio of falling time to rising time across all spectral subtypes, with the ratio being larger for short events.
We propose a novel point cloud based 3D organ segmentation pipeline utilizing deep Q-learning. In order to preserve shape properties, the learning process is guided using a statistical shape model. The trained agent directly predicts piece-wise linear transformations for all vertices in each iteration. This mapping between the ideal transformation for an object outline estimation is learned based on image features. To this end, we introduce aperture features that extract gray values by sampling the 3D volume within the cone centered around the associated vertex and its normal vector. Our approach is also capable of estimating a hierarchical pyramid of non rigid deformations for multi-resolution meshes. In the application phase, we use a marginal approach to gradually estimate affine as well as non-rigid transformations. We performed extensive evaluations to highlight the robust performance of our approach on a variety of challenge data as well as clinical data. Additionally, our method has a run time ranging from 0.3 to 2.7 seconds to segment each organ. In addition, we show that the proposed method can be applied to different organs, X-ray based modalities, and scanning protocols without the need of transfer learning. As we learn actions, even unseen reference meshes can be processed as demonstrated in an example with the Visible Human. From this we conclude that our method is robust, and we believe that our method can be successfully applied to many more applications, in particular, in the interventional imaging space.
We propose a transformer-based neural network architecture for multi-object 3D reconstruction from RGB videos. It relies on two alternative ways to represent its knowledge: as a global 3D grid of features and an array of view-specific 2D grids. We progressively exchange information between the two with a dedicated bidirectional attention mechanism. We exploit knowledge about the image formation process to significantly sparsify the attention weight matrix, making our architecture feasible on current hardware, both in terms of memory and computation. We attach a DETR-style head on top of the 3D feature grid in order to detect the objects in the scene and to predict their 3D pose and 3D shape. Compared to previous methods, our architecture is single stage, end-to-end trainable, and it can reason holistically about a scene from multiple video frames without needing a brittle tracking step. We evaluate our method on the challenging Scan2CAD dataset, where we outperform (1) recent state-of-the-art methods for 3D object pose estimation from RGB videos; and (2) a strong alternative method combining Multi-view Stereo with RGB-D CAD alignment. We plan to release our source code.
We study the conditions under which an analog acoustic geometry of a relativistic fluid in flat spacetime can take the same form as the Schwarzschild black hole geometry. We find that the speed of sound must necessarily be equal to the speed of light. Since the speed of the fluid cannot exceed the speed of light, this implies that analog Schwarzschild geometry necessarily breaks down behind the horizon.
In principle, non-Hermitian quantum equations of motion can be formulated using as a starting point either the Heisenberg's or the Schr\"odinger's picture of quantum dynamics. Here it is shown in both cases how to map the algebra of commutators, defining the time evolution in terms of a non-Hermitian Hamiltonian, onto a non-Hamiltonian algebra with a Hermitian Hamiltonian. The logic behind such a derivation is reversible, so that any Hermitian Hamiltonian can be used in the formulation of non-Hermitian dynamics through a suitable algebra of generalized (non-Hamiltonian) commutators. These results provide a general structure (a template) for non-Hermitian equations of motion to be used in the computer simulation of open quantum systems dynamics.
Understanding the electrical manipulation of antiferromagnetic order is a crucial aspect to enable the design of antiferromagnetic devices working at THz frequency. Focusing on collinear insulating antiferromagnetic NiO/Pt thin films as a materials platform, we identify the crystallographic orientation of the domains that can be switched by currents and quantify the N\'eel vector direction changes. We demonstrate electrical switching between different T-domains by current pulses, finding that the N\'eel vector orientation in these domains is along $[\pm5\ \pm5\ 19]$, different compared to the bulk $<11\bar{2}>$ directions. The final state of the N\'eel vector $\textbf{n}$ switching after current pulses $\textbf{j}$ along the $[1\ \pm1\ 0]$ directions is $\textbf{n}\parallel \textbf{j}$. By comparing the observed N\'eel vector orientation and the strain in the thin films, assuming that this variation arises solely from magnetoelastic effects, we quantify the order of magnitude of the magnetoelastic coupling coefficient as $b_{0}+2b_{1}=3*10^7 J\ m^{-3}$ . This information is key for the understanding of current-induced switching in antiferromagnets and for the design and use of such devices as active elements in spintronic devices.
Thin films of silver containing 0.3 - 1.5 at % Fe have been prepared by vapor co-deposition. Depending on substrate temperature and iron concentration we could systematically follow the formation of nanometer size clusters of iron from initially dilute iron monomers. samples were characterized via X-ray diffraction, resistivity and M\"{o}ssbauer spectroscopic measurements. The magnetic behavior derived from M\"{o}ssbauer data can be best described with an ensemble of ferromagnetic mono-domain particles. The magnetic freezing observed at low temperatures, is controlled via the inter-particle interactions mediated via conduction electron polarization, i.e. RKKY interaction. The interaction of the cluster magnetic moments with the conduction electron sea is best quantified by the electrical resistivity data. For all studied concentrations we find a non-monotonic variation with temperature which can be understood by competing shielding of the cluster moments by conduction electron spin scattering due to Kondo effect and the magnetic coupling.
We study the decoherence properties of a certain class of Markovian quantum open systems from both the Decohering Histories and Environment Induced Superselection paradigms. The class studied includes many familiar quantum optical cases. For this class, we show that there always exists a basis which leads to {\em exactly} consistent histories for any coarse graining {\em irrespective} of the initial conditions. The magnitude of the off--diagonal elements of the reduced density matrix $\rho$ in this basis however, depends on the initial conditions. Necessary requirements for classicality as advanced by the two paradigms are thus in direct conflict in these systems.
ASASSN-13db is a M5-type star with a protoplanetary disk, the lowest mass star known to experience accretion outbursts. Since its discovery in 2013, it has experienced two outbursts, the second of which started in November 2014 and lasted until February 2017. We use high- and low-resolution spectroscopy and time-resolved photometry from the ASAS-SN survey, the LCOGT and the Beacon Observatory to study the lightcurve and the dynamical and physical properties of the accretion flow. The 2014-2017 outburst lasted for nearly 800 days. A 4.15d period in the lightcurve likely corresponds to rotational modulation of a star with hot spot(s). The spectra show multiple emission lines with variable inverse P-Cygni profiles and a highly variable blueshifted absorption below the continuum. Line ratios from metallic emission lines (Fe I/Fe II, Ti I/Ti II) suggest temperatures of $\sim$5800-6000 K in the accretion flow. Photometrically and spectroscopically, the 2014-2017 event displays an intermediate behavior between EXors and FUors. The accretion rate (\.{M}=1-3$\times$10$^{-7}$M$_\odot$/yr), about 2 orders of magnitude higher than the accretion rate in quiescence, is not significantly different from the accretion rate observed in 2013. The absorption features in the spectra suggest that the system is viewed at a high angle and drives a powerful, non-axisymmetric wind, maybe related to magnetic reconnection. The properties of ASASSN-13db suggest that temperatures lower than those for solar-type stars are needed for modeling accretion in very low-mass systems. Finally, the rotational modulation during the outburst reveals that accretion-related structures settled after the begining of the outburst and can be relatively stable and long-lived. Our work also demonstrates the power of time-resolved photometry and spectroscopy to explore the properties of variable and outbursting stars. (Abridged).
The correlation between the directions of optically-detected AGNs within 75 Mpc and the arrival directions of cosmic rays above 57 EeV detected by the Auger collaboration up to August 2007 is examined using uniform-exposure plots and a form of right ascension resonance which does not require choice of an association window radius. Using the latter, the chance of accidental correlation is found to be well below 1 in 10^5 even without using 3.2 degree windows; the correlation with FRI-like radio galaxies within 75 Mpc, listed by Nagar & Matulich (which are in AGN clusters), is separately just as significant; and a correlation can also be found in other data at a lower energy. Cen A is currently inactive at this energy, as more distant radio galaxies are so prominent. The efficacy of a 57 EeV cut to select this revelatory (proton) sample of the Auger data may be almost accidental and not robust. The cosmic rays in the Auger sample seem to be scattered by ~3-4 degrees en route, from about 50 Mpc, and in one relatively well probed sky region there may be a 4 degree systematic deflection in a Bz component of the magnetic field in the galactic halo. The sources appear to be mostly within 120 Mpc. This is compatible with a GZK survival horizon, but only if (a) the Auger energies are underestimated by ~25% and (b) the sudden fall in the energy spectrum is not simply a GZK effect but essentially reflects an energy cut-off in the sources.
Various systems of moment equations---consisting of up to (d+3)(d^2+6d+2)/6 moments---in a general dimension d for a dilute granular gas composed of Maxwell molecules are derived from the inelastic Boltzmann equation by employing the Grad moment method. The Navier--Stokes-level constitutive relations for the stress and heat flux appearing in the system of mass, momentum and energy balance equations are determined from the derived moment equations. It has been shown that the moment equations only for the hydrodynamic field variables (density, velocity and granular temperature), stress and heat flux---along with the time-independent value of the fourth cumulant---are sufficient for determining the Navier--Stokes-level constitutive relations in the case of inelastic Maxwell molecules, and that the other higher-order moment equations do not play any role in this case. The homogeneous cooling state of a freely cooling granular gas is investigated with the system of the Grad (d+3)(d^2+6d+2)/6-moment equations and its various subsystems. By performing a linear stability analysis in the vicinity of the homogeneous cooling state, the critical system size for the onset of instability is estimated through the considered Grad moment systems. The results on critical system size from the presented moment theories are found to be in reasonably good agreement with those from simulations.
We deal with the problem to find the number $P(b)$ of integer non-negative solutions of an equation $\sum_{i=1}^{n} a_i x_i=b$, where $a_1,a_2,...,a_n$ are natural numbers and $b$ is a non-negative integer. As different from the traditional methods of investigation of the function $P(b)$, in our study we do not employ the techniques of number series theory, but use in the main the properties of the Kronecker function and the elements of combinatorics. The formula is derived to express $P(b)$, for an integer non-negative $b$, via $P(r)$, $P(r+M)$,..., $P(r+(s-1)M)$ when $s\neq 0$, where $s=\left[ n-\dfrac{\sum_{i=1}^{n}a_i+r}{M} \right]$ and takes quite small values in some particular cases; $M$ is the least common multiple of the numbers $a_1,a_2,\ldots,a_n$, and $r$ is the remainder of $b$ modulo $M$. Also, the recurrent formulas are derived to calculate $P(b)$, for any non-negative integer $b$, which, in particular, are used in finding $P(r)$, $P(r+M)$,..., $P(r+(s-1)M)$. For the case where $s=0$ and $a_1$, $a_2$,..., $a_n$ are coprime, the explicit formula $P(b)=\dfrac{M^{n-1}}{a_1a_2\ldots a_n}C^{n-1}_{\left[\dfrac{b}{M}\right]+n-1}$ is given. To illustrate the proposed method, examples of finding the function $P(b)$ for linear Diophantine equations with $2,3,7$ and $n$ variables are given.
The conventional wisdom that the rate of incidence of Mg II absorption systems, dN/dz (excluding `associated systems' having velocity beta*c relative to the AGN of less than ~5000 km/s) is totally independent of the background AGN, has been challenged by a recent finding that dN/dz for strong Mg II absorption systems towards distant blazars is 2.2 \pm_{0.6}^{0.8} times the value known for normal optically-selected quasars (QSOs). This has led to the suggestion that a significant fraction of even the absorption systems with beta as high as 0.1 may have been ejected by the relativistic jets in the blazars, which are expected to be pointed close to our direction. Here we investigate this scenario using a large sample of 115 flat-spectrum radio-loud quasars (FSRQs) which too possess powerful jets, but are only weakly polarized. We show, for the first time, that dN/dz towards FSRQs is, on the whole, quite similar to that known for QSOs and the comparative excess of strong \mgii absorption systems seen towards blazars is mainly confined to beta< 0.15. The excess relative to FSRQs can probably result from a likely closer alignment of blazar jets with our direction and hence any gas clouds accelerated by them are more likely to be on the line of sight to the active quasar nucleus.
We present the results of fitting a flexible stellar stream density model to a collection of thirteen streams around the Milky Way, using photometric data from DES, DECaLS, and Pan-STARRS. We construct density maps for each stream and characterise their tracks on the sky, width, and distance modulus curves along the length of each stream. We use these measurements to compute lengths and total luminosities of streams and identify substructures. Several streams show prominent substructures, such as stream broadening, gaps, large deviations of stream tracks and sharp changes in stream densities. Examining the group of streams as a population, as expected we find that streams with globular cluster progenitors are typically narrower than those with dwarf galaxy progenitors, with streams around 100 pc wide showing overlap between the two populations. We also note the average luminosity of globular cluster streams is significantly lower than the typical luminosity of intact globular clusters. The likely explanation is that observed globular cluster streams preferentially come from lower luminosity and lower density clusters. The stream measurements done in a uniform manner presented here will be helpful for more detailed stream studies such as identifying candidate stream members for spectroscopic follow up and stellar stream dynamical modeling.