ShantanuT01/DACTYL-Pretraining huggingface dataset:
Our PACS and SPIRE images of the Aquila Rift and part of the Polaris Flare regions, taken during the science demonstration phase of Herschel discovered fascinating, omnipresent filamentary structures that appear to be physically related to compact cores. We briefly describe a new multi-scale, multi-wavelength source extraction method used to detect objects and measure their parameters in our Herschel images. All of the extracted starless cores (541 in Aquila and 302 in Polaris) appear to form in the long and very narrow filaments. With its combination of the far-IR resolution and sensitivity, Herschel directly reveals the filaments in which the dense cores are embedded; the filaments are resolved and have deconvolved widths of 35 arcsec in Aquila and 59 arcsec in Polaris (9000 AU in both regions). Our first results of observations with Herschel enable us to suggest that in general dense cores may originate in a process of fragmentation of complex networks of long, thin filaments, likely formed as a result of an interplay between gravity, interstellar turbulence, and magnetic fields. To unravel the roles of the processes, one has to obtain additional kinematic and polarization information; these follow-up observations are planned.
This is a continuation of the paper published in {\it Phys. Rev.} {\bf D89}, 023520 (2014). It is investigated here how the luminosity distance -- redshift relation $D_L(z)$ of the $\Lambda$CDM model is duplicated in the Lema\^{\i}tre -- Tolman (L--T) model with $\Lambda = 0$, constant bang-time function $t_B$ and the energy function $E(r)$ mimicking accelerated expansion on the observer's past light cone ($r$ is a uniquely defined comoving radial coordinate). Numerical experiments show that $E > 0$ necessarily. The functions $z(r)$ and $E(r)$ are numerically calculated from the initial point at the observer's position; then backward from the initial point at the apparent horizon (AH). Reconciling the results of the two calculations allows one to determine the values of $E/r^2$ at $r = 0$ and at the AH. The problems connected with continuing the calculation through the AH are discussed in detail and solved. Then $z(r)$ and $E(r)$ are continued beyond the AH, up to the numerical crash that signals the contact of the light cone with the Big Bang. Similarly, the light cone of the L--T model is calculated by proceeding from the two initial points, and compared with the $\Lambda$CDM light cone. The model constructed here contains shell crossings, but they can be removed by matching the L--T region to a Friedmann background, without causing any conflict with the type Ia supernovae observations. The mechanism of imitating the accelerated expansion by the $E(r)$ function is explained in a descriptive way.
We present a detailed investigation of the X-ray luminosity (Lx)-gas temperature (Tvir) relation of the complete X-ray flux-limited sample of the 64 brightest galaxy clusters in the sky (HIFLUGCS). We study the influence of two astrophysical processes, active galactic nuclei (AGN) heating and intracluster medium (ICM) cooling, on the Lx-Tvir relation, simultaneously for the first time. We determine best-fit relations for different subsamples using the cool-core strength and the presence of central radio activity as selection criteria. We find the strong cool-core clusters (SCCs) with short cooling times (< 1Gyr)to display the steepest relation (Lx ~ Tvir^{3.33}) and the non-cool-core clusters (NCCs) with long cooling times (> 7.7Gyr) to display the shallowest (Lx ~ Tvir^{2.42}). This has the simple implication that on the high-mass scale (Tvir > 2.5keV) the steepening of the Lx-Tvir relation is mainly due to the cooling of the intracluster medium gas. We propose that ICM cooling and AGN heating are both important in shaping the Lx-Tvir relation but on different length-scales. While our study indicates that ICM cooling dominates on cluster scales (Tvir > 2.5keV), we speculate that AGN heating dominates the scaling relation in poor clusters and groups (Tvir < 2.5keV). The intrinsic scatter about the Lx-Tvir relation in X-ray luminosity for the whole sample is 45.4% and varies from a minimum of 34.8% for weak cool-core clusters to a maximum of 59.4% for clusters with no central radio source. We find that after excising the cooling region, the scatter in the Lx-Tvir relation drops from 45.4% to 39.1%, implying that the cooling region contributes ~ 27% to the overall scatter. Lastly, we find the true SCC fraction to be 25% lower than the observed one and the true normalizations of the Lx-Tvir relations to be lower by 12%, 7%, and 17% for SCC, WCC, and NCC clusters, respectively. [abridged]
The accuracy of information retrieval systems is often measured using complex loss functions such as the average precision (AP) or the normalized discounted cumulative gain (NDCG). Given a set of positive and negative samples, the parameters of a retrieval system can be estimated by minimizing these loss functions. However, the non-differentiability and non-decomposability of these loss functions does not allow for simple gradient based optimization algorithms. This issue is generally circumvented by either optimizing a structured hinge-loss upper bound to the loss function or by using asymptotic methods like the direct-loss minimization framework. Yet, the high computational complexity of loss-augmented inference, which is necessary for both the frameworks, prohibits its use in large training data sets. To alleviate this deficiency, we present a novel quicksort flavored algorithm for a large class of non-decomposable loss functions. We provide a complete characterization of the loss functions that are amenable to our algorithm, and show that it includes both AP and NDCG based loss functions. Furthermore, we prove that no comparison based algorithm can improve upon the computational complexity of our approach asymptotically. We demonstrate the effectiveness of our approach in the context of optimizing the structured hinge loss upper bound of AP and NDCG loss for learning models for a variety of vision tasks. We show that our approach provides significantly better results than simpler decomposable loss functions, while requiring a comparable training time.
We investigate ground-state properties of a $t_{\rm 2g}$-orbital Hubbard model on a zigzag chain relevant for CaV$_{2}$O$_{4}$, by exploiting numerical techniques such as Lanczos diagonalization and density-matrix renormalization group. Assuming a V$^{3+}$ ion, a local spin $S$=$1$ state is formed by two electrons in the $t_{\rm 2g}$ orbitals. That is, the system is a Haldane system with active $t_{\rm 2g}$-orbital degrees of freedom. We observe orbital-state transitions, yielding a distinct spin system under the orbital-ordered background. We also discuss the orbital structure induced by open edges, originating in the spatial anisotropy of the $t_{\rm 2g}$ orbitals.
We describe an explicit `higher rank' Iwasawa theory for zeta elements associated to the multiplicative group over abelian extensions of general number fields. We then show that this theory leads to a concrete new strategy for proving special cases of the equivariant Tamagawa number conjecture. As a first application of this approach, we use it to prove new cases of the conjecture for Tate motives over natural families of abelian CM extensions of totally real fields for which the relevant $p$-adic $L$-functions possess trivial zeroes.
Wave motion in two- and three-dimensional periodic lattices of beam members supporting longitudinal and flexural waves is considered. An analytic method for solving the Bloch wave spectrum is developed, characterized by a generalized eigenvalue equation obtained by enforcing the Floquet condition. The dynamic stiffness matrix is shown to be explicitly Hermitian and to admit positive eigenvalues. Lattices with hexagonal, rectangular, tetrahedral and cubic unit cells are analyzed. The semi-analytical method can be asymptotically expanded for low frequency yielding explicit forms for the Christoffel matrix describing wave motion in the quasistatic limit.
We present wide-field, high-resolution imaging observations in 12CO 3-2 and H2 1-0 S(1) towards a ~1 square degree region of NGC2264. We identify 46 H2 emission objects, of which 35 are new discoveries. We characterize several cores as protostellar, reducing the previously observed ratio of prestellar/protostellar cores in the NGC2264 clusters. The length of H2 jets increases the previously reported spatial extent of the clusters. In each cluster, <0.5% of cloud material has been perturbed by outflow activity. A principal component analysis of the 12CO data suggests that turbulence is driven on scales >2.6 pc, which is larger than the extent of the outflows. We obtain an exponent alpha=0.74 for the size-linewidth relation, possibly due to the high surface density of NGC2264. In this very active, mixed-mass star forming region, our observations suggest that protostellar outflow activity is not injecting energy and momentum on a large enough scale to be the dominant source of turbulence.
The main goal of the paper is to study the origins of a contradiction between the Weinberg theorem B-A=\lambda and the `longitudinality' of an antisymmetric tensor field (and of a Weinberg field which is equivalent to it), transformed on the (1,0)\oplus (0,1) Lorentz group representation. On the basis of analysis of dynamical invariants in the Fock space situation has been partly clarified.
Roger Penrose proposed that a spatial quantum superposition collapses as a back-reaction from spacetime, which is curved in different ways by each branch of the superposition. In this sense, one speaks of gravity-related wave function collapse. He also provided a heuristic formula to compute the decay time of the superposition $\mathord{-}$ similar to that suggested earlier by Lajos Di\'osi, hence the name Di\'osi-Penrose model. The collapse depends on the effective size of the mass density of particles in the superposition, and is random: this randomness shows up as a diffusion of the particles' motion, resulting, if charged, in the emission of radiation. Here, we compute the radiation emission rate, which is faint but detectable. We then report the results of a dedicated experiment at the Gran Sasso underground laboratory to measure this radiation emission rate. Our result sets a lower bound on the effective size of the mass density of nuclei, which is about three orders of magnitude larger than previous bounds. This rules out the natural parameter-free version of the Di\'osi-Penrose model.
A "truncation" of Pascal's triangle is a triangular array of numbers that satisfies the usual Pascal recurrence but with a boundary condition that declares some terminal set of numbers along each row of the array to be zero. Presented here is a family of natural truncations of Pascal's triangle that generalize a kind of Catalan triangle. The numbers in each array are realized as differences of binomial coefficients, as counts of certain lattice paths and tableaux, and as entries of representing matrices for certain linear transformations of polynomial spaces. Lucas's theorem is applied to determine precisely those truncations for which the number of odd entries on each row is a power of two.
The self-assembly mechanism of one-end-open carbon nanotubes (CNTs) suspended in an aqueous solution was studied by molecular dynamics simulations. It was shown that two one-end-open CNTs with different diameters can coaxially self-assemble into a nanocapsule. The nanocapsules formed were stable in aqueous solution under ambient conditions, and the pressure inside the nanocapsule was much higher than the ambient pressure due to the van der Waals interactions between two parts of the nanocapsule. The effect of the normalized radius difference, normalized inter-tube distance and aspect ratio of the CNT pairs were systematically explored. The electric field response of nanocapsules was studied with ab initio molecular dynamics simulations, which shows that nanocapsules can be opened by applying an external electric field, due to the polarization of carbon atoms. This discovery not only sheds light on a simple yet robust nanocapsule self-assembly mechanism, but also underpins potential innovations in drug delivery, nano-reactors, etc.
In this paper a short review of the theoretical problems of the pionic radioactivity as a new nuclear mode is presented. The essential theoretical and experimental results obtained in the 25 years from the prediction of the nuclear pionic radioactivity are reviewed. Using the fission-like model it was shown that most of the SHE-nuclei lie in the region where the pionic fissility parameters attain their limiting value X=1 (see Fig.2-3). Hence, the SHE-region is characterized by the absence of a classical barrier toward spontaneous pion emission. Consequently, both decay modes, the pionic fission and the spontaneous fission of SHE nuclides, essentially will be determined only by shell effects. Then, it was seen that the usual predicted SHE-island of stability around the double magic nucleus 298-[114], which is not confirmed experimentally, can be explained by the dominant pionic radioactivity of the SHE-nuclei from this region. The bimodal symmetric (see Figs. 5ab) as well as, the supergiant radioactive halos (see Fig. 6) as two important signature of the nuclear pionic fission are evidentiated.
We consider a stochastic energy exchange model that models the 1D microscopic heat conduction in the nonequilibrium setting. In this paper, we prove the existence and uniqueness of the nonequilibrium steady state (NESS) and, furthermore, the polynomial speed of convergence to the NESS. Our result shows that the asymptotic properties of this model and its deterministic dynamical system origin are consistent. The proof uses a new technique called the induced chain method. We partition the state space and work on both the Markov chain induced by an "active set" and the tail of return time to this "active set".
We perform N-body simulations of young triple systems consisting of two low-mass companions orbiting around a significantly more massive primary. We find that, when the orbits of the companions are coplanar and not too widely separated, the chance of a collision between the two companions can be as high as 20 per cent. Collisions between one of the companions (always the less massive) and the primary can also occur in systems with unequal-mass companions. The chance of collisions is a few per cent in systems with more realistic initial conditions, such as with slightly non-coplanar orbits and unequal-mass companions. If the companions start widely separated then collision are very rare except in some cases when the total mass of the companions is large. We suggest that collisions between members of young multiple systems may explain some unusual young multiple systems such as apparently non-coeval companions.
We show that the previously introduced concept of distance on statistical spaces leads to a straightforward definition of differential entropy on these statistical spaces. These spaces are characterized by the fact that their points can only be localized within a certain volume and exhibit thus a feature of fuzziness. This implies that Riemann integrability of relevant integrals is no longer secured. Some discussion on the specialization of this formalism to quantum states concludes the paper.
Electrical conductivity of porous silicon fabricated form heavily doped p-type silicon is very sensitive to NO$_2$, even at concentrations below 100 ppb. However, sensitivity strongly depends on the porous microstructure. The structural difference between sensitive and insensitive samples is independently confirmed by microscopy images and by light scattering behavior. A way to change the structure is by modifying the composition of the electrochemical solution. We have found that best results are achieved using ethanoic solutions with HF concentration levels between 13% and 15%.
Recent experiments in the integer quantum Hall regime seem to find direct transitions from a quantum Hall state with Hall conductance $\sigma_{xy} = n e^2/h $ with integer $n > 1$, to an insulating state in weak magnetic fields. We study this issue using a variation of the tight-binding lattice model for non-interacting electrons. Although quantum Hall transitions with change in Hall conductance $n e^2/ h$ with $n > 1$ do exist in our model for special tuning of parameters, they generically split into quantum Hall transitions with the Hall conductance changing by $e^2 / h$ at each transition. This suggests that a generic multiple step quantum Hall transition is incompatible with a non-interacting electron picture.
We develop a thermodynamical model of fermionic dark matter halos at finite temperature. Statistical equilibrium states may be justified by a process of violent collisionless relaxation in the sense of Lynden-Bell or from a collisional relaxation of nongravitational origin if the fermions are self-interacting. The most probable state (maximum entropy state) generically has a "core-halo" structure with a quantum core (fermion ball) surrounded by an isothermal atmosphere. The quantum core is equivalent to a polytrope of index $n=3/2$. The Pauli exclusion principle creates a quantum pressure that prevents gravitational collapse and solves the core-cusp problem of the cold dark matter model. The isothermal atmosphere (which is similar to the NFW profile of cold dark matter) accounts for the flat rotation curves of the galaxies at large distances. We numerically solve the equation of hydrostatic equilibrium with the Fermi-Dirac equation of state and determine the density profiles and rotation curves of fermionic dark matter halos.
A doped semiconductor double-quantum-dot molecule is proposed as a qubit realization. The quantum information is encoded in the electron spin, thus benefiting from the long relevant decoherence times; the enhanced flexibility of the molecular structure allows to map the spin degrees of freedom onto the orbital ones and vice versa, and opens the possibility for high-finesse (conditional and unconditional) quantum gates by means of stimulated Raman adiabatic passage.
Simulating quantum systems constructively furthers our understanding of qualitative and quantitative features which may be analytically intractable. In this letter, we directly simulate and explore the entanglement structure present in a paradigmatic example of quantum information: Shor's wavefunction. The methodology employed is a dynamical tensor network which is initially constructed as a tree tensor network, inspired by the modular exponentiation quantum circuit, and later efficiently mapped to a matrix product state. Utilizing the Schmidt number as a local entanglement metric, our construction explicitly captures the wavefunction's non-local entanglement structure and an entanglement scaling relation is discovered. Specifically, we see that entanglement across a bipartition grows exponentially in the number of qubits before saturating at a critical scale which is proportional to the modular periodicity.
Using a density functional based electronic structure method, we study the effect of crystalline dielectrics on the metallic surface states of Bismuth- and chalcogen-based binary and ternary three dimensional topological insulator (TI) thin films. Crystalline quartz (SiO2) and boron nitride (BN) dielectrics were considered. Crystalline approximation to the amorphous quartz allows to study the effect of oxygen coverage or environmental effects on the surface states degradation which has gained attention recently in the experimental community. We considered both symmetric and asymmetric dielectric cappings to the sufaces of TI thin films. Our studies suggest that BN and quartz cappings have negligible effects on the Dirac cone surface states of both binary and ternary TIs, except in the case of an oxygen-terminated quartz surface. Dangling bond states of oxygens in oxygen-terminated quartz dominate the region close to Fermi level, thereby distorting the TI Dirac cone feature and burying the Dirac point in the quartz valence band region. Passivating the oxygen-terminated surface with atomic hydrogen removes these dangling bond states from the Fermi surface region, and consequently the clear Dirac cone is recovered. Our results are consistent with recent experimental studies of TI surface degradation in the presence of oxygen coverage.
We study a large sample of RXTE PCA/HEXTE observations of Cyg X-1. We characterize the spectra by soft and hard X-ray colours (which define the spectral states), and fit them with a physical model of hybrid, thermal/non-thermal Comptonization. We then fit the power spectra by a sum of Lorentzians. We show the resulting correlations between the spectral colour (defining the hard, intermediate and soft spectral states), the Comptonization amplification factor, the fractional Compton reflection strength, and the peak frequency of the Lorentzians. We also calculate the fractional variability (rms) as a function of photon energy. We fit the obtained rms dependencies by physical models of varying accretion rate, a varying soft-photon input from an outer disc to a hot inner plasma, and a varying dissipation rate in a hot corona above a disc.
The origin of the asymmetric supernova remnant (SNR) W49B has been a matter of debate: is it produced by a rare jet-driven core-collapse supernova, or by a normal supernova that is strongly shaped by its dense environment? Aiming to uncover the explosion mechanism and origin of the asymmetric, centrally filled X-ray morphology of W49B, we have performed spatially resolved X-ray spectroscopy and a search for potential point sources. We report new candidate point sources inside W49B. The Chandra X-ray spectra from W49B are well-characterized by two-temperature gas components ($\sim 0.27$ keV + 0.6--2.2 keV). The hot component gas shows a large temperature gradient from the northeast to the southwest and is over-ionized in most regions with recombination timescales of 1--$10\times 10^{11}$ cm$^{-3}$ s. The Fe element shows strong lateral distribution in the SNR east, while the distribution of Si, S, Ar, Ca is relatively smooth and nearly axially symmetric. Asymmetric Type-Ia explosion of a Chandrasekhar-mass white dwarf well-explains the abundance ratios and metal distribution of W49B, whereas a jet-driven explosion and normal core-collapse models fail to describe the abundance ratios and large masses of iron-group elements. A model based on a multi-spot ignition of the white dwarf can explain the observed high $M_{\rm Mn}/M_{\rm Cr}$ value (0.8--2.2). The bar-like morphology is mainly due to a density enhancement in the center, given the good spatial correlation between gas density and X-ray brightness. The recombination ages and the Sedov age consistently suggest a revised SNR age of 5--6 kyr. This study suggests that despite the presence of candidate point sources projected within the boundary of this SNR, W49B is likely a Type-Ia SNR, which suggests that Type-Ia supernovae can also result in mixed-morphology SNRs.