ShantanuT01/DACTYL-Pretraining huggingface dataset:
Using an atomistic first principles approach, we investigate the band offset of the GaAs/AlxGa1-xAs heterojunctions for the entire range of the Al doping concentration 0<x<=1. We apply the coherent potential approach to handle the configuration average of Al doping and a recently proposed semi-local exchange potential to accurately determine the band gaps of the materials. The calculated band structures of the GaAs, AlAs crystals and band gaps of the GaAs/AlxGa1-xAs alloys, are in very good agreement with the experimental results. We predict that valence band offset of the GaAs/AlxGa1-xAs heterojunction scales with the Al concentration x in a linear fashion as VBO(x)~0.587 x, and the conduction band offset scales with x in a nonlinear fashion. Quantitative comparisons to the corresponding experimental data are made.
Mott metal-insulator transitions in an M-fold orbitally degenerate Hubbard model are studied by means of a generalization of the linearized dynamical mean-field theory. The method allows for an efficient and reliable determination of the critical interaction U_c for any integer filling n and different M at zero temperature. For half-filling a linear dependence of U_c on M is found. Inclusion of the (full) Hund's rule exchange J results in a strong reduction of U_c. The transition turns out to change qualitatively from continuous for J=0 to discontinuous for any finite J.
This paper studies integer solutions to the ABC equation A+B+C=0 in which none of A, B, C has a large prime factor. Set H(A,B, C)= max(|A|,|B|,|C|) and set the smoothness S(A, B, C) to be the largest prime factor of ABC. We consider primitive solutions (gcd(A, B, C)=1) having smoothness no larger than a fixed power p of log H. Assuming the abc Conjecture we show that there are finitely many solutions if p<1. We discuss a conditional result, showing that the Generalized Riemann Hypothesis (GRH) implies there are infinitely many primitive solutions when p>8. We sketch some details of the proof of the latter result.
The all-sky maps of the observed variation of the Hubble constant can be reproduced from a theoretical point of view by introducing an intergalactic plasma with a variable number density of electrons. The observed averaged value and variance of the Hubble constant are reproduced by adopting a rim model, an auto-gravitating model, and a Voronoi diagrams model as the backbone for an auto-gravitating medium. We also analyze an astronomer's model based on the 3D spatial distribution of galaxies as given by the 2MASS Redshift Survey and an auto-gravitating Lane--Emden ($n=5$) profile of the electrons. The simulation which involves the Voronoi diagrams is done in a cubic box with sides of 100 Mpc. The simulation which involves the 2MASS covers the range of redshift smaller than 0.05.
To help accelerate progress in multi-target, multi-camera tracking systems, we present (i) a new pair of precision-recall measures of performance that treats errors of all types uniformly and emphasizes correct identification over sources of error; (ii) the largest fully-annotated and calibrated data set to date with more than 2 million frames of 1080p, 60fps video taken by 8 cameras observing more than 2,700 identities over 85 minutes; and (iii) a reference software system as a comparison baseline. We show that (i) our measures properly account for bottom-line identity match performance in the multi-camera setting; (ii) our data set poses realistic challenges to current trackers; and (iii) the performance of our system is comparable to the state of the art.
Magnetic Weyl semimetals with broken time-reversal symmetry are expected to generate strong intrinsic anomalous Hall effects, due to their large Berry curvature. Here, we report a magnetic Weyl semimetal candidate Co3Sn2S2 with a quasi-two-dimensional crystal structure consisting of stacked Kagome lattices. This lattice provides an excellent platform for hosting exotic quantum topological states. We observe a negative magnetoresistance that is consistent with the chiral anomaly expected from the presence of Weyl fermions close to the Fermi level. The anomalous Hall conductivity is robust against both increased temperature and charge conductivity, which corroborates the intrinsic Berry-curvature mechanism in momentum space. Owing to the low carrier density in this material and the significantly enhanced Berry curvature from its band structure, the anomalous Hall conductivity and the anomalous Hall angle simultaneously reach 1130 S cm-1 and 20%, respectively, an order of magnitude larger than typical magnetic systems. Combining the Kagome-lattice structure and the long-range out-of-plane ferromagnetic order of Co3Sn2S2, we expect that this material is an excellent candidate for observation of the quantum anomalous Hall state in the two-dimensional limit.
The spectrum of the interior transmission problem is related to the unique determination of the acoustic properties of a body in thermoacoustic imaging. Under a non-trapping hypothesis, we show that sparsity of the interior transmission spectrum implies a range separation condition for the thermoacoustic operator. In odd dimension greater than or equal to three, we prove that the transmission spectrum for a pair of radially symmetric non-trapping sound speeds is countable, and conclude that the ranges of the associated thermoacoustic maps have only trivial intersection.
The main sulfur-bearing molecules OCS, H2S, SO, SO2, and CS have been observed in four high mass dense cores (W43-MM1, IRAS 18264, IRAS 05358, and IRAS 18162). Our goal is to put some constraints on the relative evolutionary stage of these sources by comparing these observations with time-dependent chemical modeling. We used the chemical model Nahoon, which computes the gas-phase chemistry and gas-grain interactions of depletion and evaporation. Mixing of the different chemical compositions shells in a 1D structure through protostellar envelope has been included since observed lines suggest nonthermal supersonic broadening. Observed radial profiles of the temperature and density are used to compute the chemistry as a function of time. With our model, we underproduce CS by several orders of magnitude compared to the other S-bearing molecules, which seems to contradict observations, although some uncertainties in the CS abundance observed at high temperature remain. The OCS/SO2, SO/SO2, and H2S/SO2 abundance ratios could in theory be used to trace the age of these massive protostars since they show a strong dependence with time, but the sources are too close in age compared to the accuracy of chemical models and observations. Our comparison between observations and modeling may, however, indicate that W43-MM1 could be chemically younger than the three other sources. Turbulent diffusivity through the protostellar envelopes has to be less efficient than 2e14 cm2s-1. Otherwise, it would have smoothed out the abundance profiles, and this would have been observed. The sulfur chemistry depends strongly on the 1D physical conditions. In our case, no conclusion can be given on the relative age of IRAS 18264, IRAS 18162 and IRAS 05358 except that they are very close. W43-MM1 seems younger than the other sources.
The CoRoT (Convection, Rotation and planetary Transits) space mission provides a valuable opportunity to monitor stars with uninterrupted time sampling for up to 150 days at a time. The study of RR Lyrae stars, performed in the framework of the Additional Programmes belonging to the exoplanetary field, will particularly benefit from such dense, long-duration monitoring. The Blazhko effect in RR Lyrae stars is a long-standing, unsolved problem of stellar astrophysics. We used the CoRoT data of the new RR Lyrae variable CoRoT 101128793 (f0=2.119 c/d, P=0.4719296 d) to provide us with more detailed observational facts to understand the physical process behind the phenomenon. The CoRoT data were corrected for one jump and the long-term drift. We applied different period-finding techniques to the corrected timeseries to investigate amplitude and phase modulation. We detected 79 frequencies in the light curve of CoRoT 101128793. They have been identified as the main frequency f0, and its harmonics, two independent terms, the terms related to the Blazhko frequency, and several combination terms. A Blazhko frequency fB=0.056 c/d and a triplet structure around the fundamental radial mode and harmonics were detected, as well as a long-term variability of the Blazhko modulation. Indeed, the amplitude of the main oscillation is decreasing along the CoRoT survey. The Blazhko modulation is one of the smallest observed in RR Lyrae stars. Moreover, the additional modes f1=3.630 and f2=3.159 c/d are detected. Taking its ratio with the fundamental radial mode into account, the term f1 could be the identified as the second radial overtone. Detecting of these modes in horizontal branch stars is a new result obtained by CoRoT.
Binding energies of three-body systems of the type \phi+2N are estimated. Due to the strong attraction between \phi-meson and nucleon, suggested in different approaches, bound states can appear in systems like \phi+np (singlet and triplet) and \phi+pp. This indicates the principal possibility of the formation of new nuclear clusters.
We comparatively study the excitonic insulator state in the extended Falicov-Kimball model (EFKM, a spinless two-band model) on the two-dimensional square lattice using the variational cluster approximation (VCA) and the cluster dynamical impurity approximation (CDIA). In the latter, the particle-bath sites are included in the reference cluster to take into account the particle-number fluctuations in the correlation sites. We thus calculate the particle-number distribution, order parameter, ground-state phase diagram, anomalous Green's function, and pair coherence length, thereby demonstrating the usefulness of the CDIA in the discussion of the excitonic condensation in the EFKM.
We study the conductivity of two-dimensional interacting electrons on the half-filled $N$th Landau level with $N \gg 1$ in the presence of the quenched disorder. The existence of the unidirectional charge-density wave state at temperature $T<T_c$, where $T_c$ is the transition temperature, leads to the anisotropic conductivity tensor. We find that the leading anisotropic corrections are proportional to $(T_c-T)/T_c$ just below the transition in accordance with the experimental findings. Above $T_c$ the correlations corresponding to the unidirectional charge-density wave state below $T_c$ result in the corrections to the conductivity proportional to $\sqrt{T_c/(T-T_c)}$.
The origin of self-similar (according to Y.Kulakov) structure of the Universe is discussed from a position of the theory of dynamic systems (DS). A probable nature of the isomorphism of DS configurations of different levels is revealed. Nucleon DS configuration like black hole (BH) might be acquired by the last as a result of Hawking radiation of initial BH and serve further as a genome of the Universe development.
We consider general aspects of N=2 gauge theories in three dimensions, including their multiplet structure, anomalies and non-renormalization theorems. For U(1) gauge theories, we discuss the quantum corrections to the moduli space, and their relation to ``mirror symmetries'' of 3d N=4 theories. Mirror symmetry is given an interpretation in terms of vortices. For SU(N_c) gauge groups with N_f fundamental flavors, we show that, depending on the number of flavors, there are quantum moduli spaces of vacua with various phenomena near the origin.
Karhunen-Loeve expansions (KLE) of stochastic processes are important tools in mathematics, the sciences, economics, and engineering. However, the KLE is primarily useful for those processes for which we can identify the necessary components, i.e., a set of basis functions, and the distribution of an associated set of stochastic coefficients. Our ability to derive these components explicitly is limited to a handful processes. In this paper we derive all the necessary elements to implement the KLE for a square-integrable Levy process. We show that the eigenfunctions are sine functions, identical to those found in the expansion of a Wiener process. Further, we show that stochastic coefficients have a jointly infinitely divisible distribution, and we derive the generating triple of the first d coefficients. We also show, that, in contrast to the case of the Wiener process, the coefficients are not independent unless the process has no jumps. Despite this, we develop a series representation of the coefficients which allows for simulation of any process with a strictly positive Levy density. We implement our theoretical results by simulating the KLE of a variance gamma process.
We obtained late-time optical and near-IR imaging of SN 2008S with the Large Binocular Telescope (LBT). We find that (1) it is again invisible at optical (UBVR) wavelengths to magnitude limits of approximately 25 mag, and (2) while detected in the near-IR (HK) at approximately 20 mag, it is fading rapidly. The near-IR detections in March and May 2010 are consistent with dust emission at a blackbody temperature of T ~ 900 K and a total luminosity of L ~ 40000 Lsun, comparable to the luminosity of the obscured progenitor star. If it is a supernova, the near-IR emission is likely due to shock heated dust since the elapsed time from peak is too long to support a near-IR dust echo and the decline in luminosity is shallower than the 56Co slope. If it is reprocessed emission from a surviving progenitor, a dust photosphere must have reestablished itself closer to the star than before the transient (~40 AU rather than 150 AU), unless there is a second, cooler dust component that dominates at mid-IR wavelengths. The continued rapid fading at roughly constant temperature favors transient emission, but the SED peaks in the mid-IR and future Spitzer observations will be needed to close the case.
In this work I investigate the statistical properties of a huge catalog of closely interacting pairs of dark matter haloes, extracted from the Millennium Simulation database. Only haloes that reach a minimum mass greater than 8.6 \times 10^10 Msun/h (corresponding to 100 particles) are considered. Close pairs are selected if they come within a critical distance dcrit. I explore the effects of replacing dcrit = 1 Mpc/h with 200 kpc/h on the evolution of separations, lifetimes, total masses and mass ratios of these pairs.
The recent imaging of the M87 black hole at millimeter wavelengths by the Event Horizon Telescope (EHT) collaboration has triggered a renewed interest in numerical models for the accretion of magnetized plasma in the regime of general relativistic magnetohydrodynamics (GRMHD). Here non-ideal simulations, including both the resistive effects and, above all, the mean-field dynamo action due to sub-scale, unresolved turbulence, are applied for the first time to such systems in the fully nonlinear regime. Combined with the differential rotation of the disk, the dynamo process is able to produce an exponential growth of any initial seed magnetic field up to the values required to explain the observations, when the instability tends to saturate even in the absence of artificial quenching effects. Before reaching the final saturation stage we observe a secondary regime of exponential growing, where the magnetic field increases more slowly due to accretion, which is modifying the underlying equilibrium. By varying the dynamo coefficient we obtain different growth rates, though the field seems to saturate at approximately the same level, at least for the limited range of parameters explored here, providing substantial values for the MAD parameter for magnetized accretion. For reasonable values of the central mass density and the commonly employed recipes for synchrotron emission by relativistically hot electrons, our model is able to reproduce naturally the observed flux of Sgr A*, the next target for EHT.
The restricted $(m,n;N)$-online Ramsey game is a game played between two players, Builder and Painter. The game starts with $N$ isolated vertices. Each turn Builder picks an edge to build and Painter chooses whether that edge is red or blue, and Builder aims to create a red $K_m$ or blue $K_n$ in as few turns as possible. The restricted online Ramsey number $\tilde{r}(m,n;N)$ is the minimum number of turns that Builder needs to guarantee her win in the restricted $(m,n;N)$-online Ramsey game. We show that if $N=r(n,n)$, \[ \tilde{r}(n,n;N)\le \binom{N}{2} - \Omega(N\log N), \] motivated by a question posed by Conlon, Fox, Grinshpun and He. The equivalent game played on infinitely many vertices is called the online Ramsey game. As almost all known Builder strategies in the online Ramsey game end up reducing to the restricted setting, we expect further progress on the restricted online Ramsey game to have applications in the general case.
Several galaxy clusters are known to present multiple and misaligned pairs of cavities seen in X-rays, as well as twisted kiloparsec-scale jets at radio wavelengths. It suggests that the AGN precessing jets play a role in the formation of the misaligned bubbles. Also, X-ray spectra reveal that typically these systems are also able to supress cooling flows, predicted theoretically. The absence of cooling flows in galaxy clusters has been a mistery for many years since numerical simulations and analytical studies suggest that AGN jets are highly energetic, but are unable to redistribute it at all directions. We performed 3D hydrodynamical simulations of the interaction between a precessing AGN jet and the warm intracluster medium plasma, which dynamics is coupled to a NFW dark matter gravitational potential. Radiative cooling has been taken into account and the cooling flow problem was studied. We found that precession is responsible for multiple pairs of bubbles, as observed. The misaligned bubbles rise up to scales of tens of kiloparsecs, where the thermal energy released by the jets are redistributed. After $\sim 150$ Myrs, the temperature of the gas within the cavities is kept of order of $\sim 10^7$ K, while the denser plasma of the intracluster medium at the central regions reaches $T \sim 10^5$ K. The existence of multiple bubbles, at diferent directions, result in an integrated temperature along the line of sight much larger than the simulations of non-precessing jets. This result is in agreement with the observations. The simulations reveal that the cooling flows cessed $\sim 50 - 70$ Myr after the AGN jets are started.
We model the attenuation due to HI along a random line of sight (LOS) using differential distribution functions constrained from observations (Kim et al. 97) in a Monte Carlo fashion (Bershady et al. 99) as described in Tepper Garcia & Fritze-v.A. (in prep.). We generate an ensemble of thousands of lines of sight out to a given redshift z, each of them containing a random absorber population. For each LOS we calculate an absorption mask, i.e. we compute the photoelectric and Lyman-Series line absorption (as yet just for the first five Lyman transitions) caused by each absorber for a flat input spectrum, modeling line profiles as in Tepper Garcia 2006. We compute model galaxy spectra corresponding to a CSFR for redshifts in the range 0.0 < z < 4.5 using the Evolutionary Synthesis code GALEV (Bicker et al. 2004). For a given redshift, we multiply each of the masks with our input spectrum and thus obtain an ensemble of an equal number of attenuated spectra. For each of these we compute a SED in the Johnson system. Using AnalySED (Anders et al. 2006) and a set of template SEDs that include only the mean attenuation (Madau 95) for every redshift, we determine to which extent the redshifts of our simulated spectral energy distributions are recovered.
We explore the possibility and practical limitations of using a three-line approach to measure both the slope and normalization of the dust attenuation law in individual galaxies. To do this, we focus on a sample of eleven galaxies with existing ground-based Balmer H$\alpha$ and H$\beta$ measurements from slit spectra, plus space-based grism constraints on Paschen-$\beta$. When accounting for observational uncertainties, we show that one galaxy has a well-constrained dust law slope and normalization in the range expected from theoretical arguments; this galaxy therefore provides an example of what may be possible in the future. However, most of the galaxies are best-fit by unusually steep or shallow slopes. We then explore whether additional astrophysical effects or observational biases could explain the elevated Paschen-$\beta$/H$\alpha$ ratios driving these results. We find that galaxies with high Paschen-$\beta$/H$\alpha$ ratios may be explained by slightly sub-unity covering fractions ($>$97%). Alternatively, differing slit losses for different lines can have a large impact on the results, emphasizing the importance of measuring all three lines with a consistent spectroscopic aperture. We conclude that while the three-line approach to constraining the shape of the dust attenuation law in individual galaxies is promising, deep observations and a consistent observational strategy will be required to minimize observational biases and to disentangle the astrophysically interesting effect of differing covering fractions. The James Webb Space Telescope will provide more sensitive measurements of Balmer and Paschen lines for galaxies at $z\approx0.3-2$, enabling uniform constraints on the optical-infrared dust attenuation law and its intrinsic variation.
A rank one local system on the complement of a hyperplane arrangement is said to be admissible if it satisfies certain non-positivity condition at every resonant edges. It is known that the cohomology of admissible local system can be computed combinatorially. In this paper, we study the structure of the set of all non-admissible local systems in the character torus. We prove that the set of non-admissible local systems forms a union of subtori. The relations with characteristic varieties are also discussed.
The interaction between jets from active galactic nuclei (AGNs) and the intracluster medium (ICM) provides key constraints on the feeding and feedback of supermassive black holes. Much understanding about AGN feedback is gained from purely hydrodynamic models; however, whether such an approximation is adequate for the magnetized, weakly collisional ICM needs to be critically examined. For example, AGN-blown bubbles in hydrodynamic simulations are easily disrupted by fluid instabilities, making it difficult to explain the coherence of observed bubbles such as the northwest ghost bubble in Perseus. In order to investigate whether magnetic tension and viscosity in realistic conditions could preserve the bubble integrity, we performed the first Braginskii-magnetohydrodynamic simulations of jet-inflated bubbles in a medium with tangled magnetic field. We find that magnetic tension alone is insufficient to prevent bubble deformation due to large velocity shear at early stage of the evolution. Although unsuppressed anisotropic viscosity in tangled magnetic field can have similar effects as isotropic viscosity, when the pressure anisotropy is bounded by microscopic plasma instabilities, the level of viscosity is substantially limited, thereby failing to prevent bubble deformation as in the inviscid case. Our results suggest that Braginskii viscosity is unlikely to be the primary mechanism for suppressing the fluid instabilities for AGN bubbles, and it remains a challenging task to reproduce smooth and coherent bubbles as observed. Because the dynamical influence and heating of the ICM critically depend on the bubble morphology, our study highlights the fundamental role of "microphysics" on the macroscopic properties of AGN feedback processes.