ShantanuT01/DACTYL-Pretraining huggingface dataset:
We investigate the temporal fluctuations characteristic of the formation of molecular dimers from ultracold fermionic atoms via Raman photoassociation. The quantum fluctuations inherent to the initial atomic state result in large fluctuations in the passage time from atoms to molecules. Assuming degeneracy of kinetic energies of atoms in the strong coupling limit we find that a heuristic classical stochastic model yields qualitative agreement with the full quantum treatment in the initial stages of the dynamics. We also show that in contrast to the association of atoms into dimers, the reverse process of dissociation from a condensate of bosonic dimers exhibits little passage time fluctuations. Finally we explore effects due to the non-degeneracy of atomic kinetic energies.
Using Dynamical Mean Field Theory (DMFT) and Monte Carlo (MC) simulations, we study the ferromagnetic transition temperature Tc of a two-band model for Diluted Magnetic Semiconductors (DMS), varying coupling constants, hopping parameters, and carrier densities. We found that Tc is optimized at all fillings p when both impurity bands (IB) fully overlap in the same energy range, namely when the exchange couplings J and bandwidths are identical. The optimal Tc is found to be about twice larger than the maximum value obtained in the one-band model, showing the importance of multiband descriptions of DMS at intermediate J's.
An investigation of the 200 $\times$ 200 pixel 'superstamp' images of the centres of the open clusters NGC 6791 and NGC 6819 allows for the identification and study of many variable stars that were not included in the Kepler target list. KIC 2569073 (V=14.22), is a particularly interesting variable Ap star that we discovered in the NGC 6791 superstamp. With a rotational period of 14.67 days and 0.034-mag variability, it has one of the largest peak-to-peak variations of any known Ap star. Colour photometry reveals an anti-phase correlation between the $B$ band, and the $V$, $R$ and $I$ bands. This Ap star is a rotational variable, also known as an $\alpha^2$ CVn, star, and is one of only a handful of Ap stars observed by Kepler. While no change in spot period or amplitude is observed within the 4-year Kepler timeseries, the amplitude shows a large increase compared to ground-based photometry obtained two decades ago.
We study the statistics of meanders, i.e. configurations of a road crossing a river through "n" bridges, and possibly winding around the source, as a toy model for compact folding of polymers. We introduce a Monte-Carlo method which allows us to simulate large meanders up to n = 400. By performing large "n" extrapolations, we give asymptotic estimates of the connectivity per bridge R = 3.5018(3), the configuration exponent gamma = 2.056(10), the winding exponent nu = 0.518(2) and other quantities describing the shape of meanders.   Keywords : folding, meanders, Monte-Carlo, tree
Taking into account both Pauli and orbital effects of external magnetic field we compute the mean field phase diagram for charge density waves in quasi-one-dimensional electronic systems. The magnetic field can cause transitions to CDW states with two types of the shifts of wave vector from its zero-field value. It can also stabilize the field-induced charge density wave. Furthermore, the critical temperature shows peaks at a new kind of magic angles.
This study investigates Parker instability in an interstellar medium (ISM) near the Galactic plane using three-dimensional magneto-hydrodynamic simulations. Parker instability arises from the presence of a magnetic field in a plasma, wherein the magnetic buoyant pressure expels the gas and cause the gas to move along the field lines. The process is thought to induce the formation of giant molecular clouds in the Galaxy. In this study, the effects of cosmic-ray (CR) diffusion are examined. The ISM at equilibrium is assumed to comprise a plasma fluid and a CR fluid at various temperatures, with a uniform magnetic field passing through it in the azimuthal direction of the Galactic disk. After a small perturbation, the unstable gas aggregates at the footpoint of the magnetic fields and forms dense blobs. The growth rate of the instability increases with the strength of the CR diffusion. The formation of dense clouds is enhanced by the effect of cosmic rays (CRs), whereas the shape of the clouds depends sensitively on the initial conditions of perturbation.
We calculate the decay widths and branching ratios of the extra neutral boson $Z^{\prime}$ predicted by the 331 bilepton model in the framework of two different particle contents. These calculations are performed taken into account oblique radiative corrections, and Flavor Changing Neutral Currents (FCNC) under the ansatz of Matsuda as a texture for the quark mass matrices. Contributions of the order of $10^{-1}-10^{-2}$ are obtained in the branching ratios, and partial widths about one order of magnitude bigger in relation with other non- and bilepton models are also obtained. A Landau-like pole arise at 3.5 TeV considering the full particle content of the minimal model (MM), where the exotic sector is considered as a degenerated spectrum at 3 TeV scale. The Landau pole problem can be avoid at the TeV scales if a new leptonic content running below the threshold at $% 3 $ TeV is implemented as suggested by other authors.
We argue that the excess of sub-PeV/PeV neutrinos recently reported by IceCube could plausibly originate through pion-production processes in the same sources responsible for cosmic rays (CRs) with energy above the second knee around $10^{18}\,$eV. The pion production efficiency for escaping CRs that produce PeV neutrinos is required to be $\gtrsim 0.1$ in such sources. On the basis of current data, we identify semi-relativistic hypernova remants as possible sources that satisfy the requirements. By virtue of their fast ejecta, such objects can accelerate protons to EeV energies, which in turn can interact with the dense surrounding medium during propagation in their host galaxies to produce sufficient high-energy neutrinos via proton--proton ($pp$) collisions. Their accompanying gamma ray flux can remain below the diffuse isotropic gamma ray background observed by the {\it Fermi} Large Area Telescope (LAT). In order to test this scenario and discriminate from alternatives, the density of target protons/nuclei and the residence time of CRs in the interacting region are crucial uncertainties that need to be clarified. As long as the neutrinos and EeV CRs originate from the same source class, detection of $\gtrsim 10\,$PeV neutrinos may be expected within 5-10 years' operation of IceCube. Together with further observations in the PeV range, the neutrinos can help in revealing the currently unknown sources of EeV CRs.
The divergence of the thermal conductivity in the thermodynamic limit is thoroughly investigated. The divergence law is consistently determined with two different numerical approaches based on equilibrium and non-equilibrium simulations. A possible explanation in the framework of linear-response theory is also presented, which traces back the physical origin of this anomaly to the slow diffusion of the energy of long-wavelength Fourier modes. Finally, the results of dynamical simulations are compared with the predictions of mode-coupling theory.
Modern data empower observers to describe galaxies as the spatially and biographically complex objects they are. We illustrate this through case studies of four, $z\sim1.3$ systems based on deep, spatially resolved, 17-band + G102 + G141 Hubble Space Telescope grism spectrophotometry. Using full spectrum rest-UV/-optical continuum fitting, we characterize these galaxies' observed $\sim$kpc-scale structures and star formation rates (SFRs) and reconstruct their history over the age of the universe. The sample's diversity---passive to vigorously starforming; stellar masses $\log M_*/M_\odot=10.5$ to $11.2$---enables us to draw spatio-temporal inferences relevant to key areas of parameter space (Milky Way- to super-Andromeda-mass progenitors). Specifically, we find signs that bulge mass-fractions ($B/T$) and SF history shapes/spatial uniformity are linked, such that higher $B/T$s correlate with "inside-out growth" and central specific SFRs that peaked above the global average for all starforming galaxies at that epoch. Conversely, the system with the lowest $B/T$ had a flat, spatially uniform SFH with normal peak activity. Both findings are consistent with models positing a feedback-driven connection between bulge formation and the switch from rising to falling SFRs ("quenching"). While sample size forces this conclusion to remain tentative, this work provides a proof-of-concept for future efforts to refine or refute it: JWST, WFIRST, and the 30-m class telescopes will routinely produce data amenable to this and more sophisticated analyses. These samples---spanning representative mass, redshift, SFR, and environmental regimes---will be ripe for converting into thousands of sub-galactic-scale empirical windows on what individual systems actually looked like in the past, ushering in a new dialog between observation and theory.
Traditional intra prediction methods for HEVC rely on using the nearest reference lines for predicting a block, which ignore much richer context between the current block and its neighboring blocks and therefore cause inaccurate prediction especially when weak spatial correlation exists between the current block and the reference lines. To overcome this problem, in this paper, an intra prediction convolutional neural network (IPCNN) is proposed for intra prediction, which exploits the rich context of the current block and therefore is capable of improving the accuracy of predicting the current block. Meanwhile, the predictions of the three nearest blocks can also be refined. To the best of our knowledge, this is the first paper that directly applies CNNs to intra prediction for HEVC. Experimental results validate the effectiveness of applying CNNs to intra prediction and achieved significant performance improvement compared to traditional intra prediction methods.
We propose a concept of half-semiconductor antiferromagnets in which both spin-polarized valence and conduction bands belong to the same spin channel with completely compensated spontaneous magnetization. Using density functional theory plus Hubbard U (DFT+U) methods, we find a viable approach to achieve the half-semiconductor antiferromagnets through the transition metal (TM) Fe and Cr codoped boron nitride(BN) sheet. Moreover, spin gapless semiconductor antiferromagnets with zero magnetic moment are also achieved in such systems.
We present a catalogue of refined positions of 68 gamma ray burst (GRB) afterglows observed by the Swift X-ray Telescope (XRT) from the launch up to 2005 Oct 16. This is a result of the refinement of the XRT boresight calibration. We tested this correction by means of a systematic study of a large sample of X-ray sources observed by XRT with well established optical counterparts. We found that we can reduce the systematic error radius of the measurements by a factor of two, from 6.5" to 3.2" (90% of confidence). We corrected all the positions of the afterglows observed by XRT in the first 11 months of the Swift mission. This is particularly important for the 37 X-ray afterglows without optical counterpart. Optical follow-up of dark GRBs, in fact, will be more efficient with the use of the more accurate XRT positions.
We construct six infinite series of families of pairs of curves (X,Y) of arbitrarily high genus, defined over number fields, together with an explicit isogeny from the Jacobian of X to the Jacobian of Y splitting multiplication by 2, 3, or 4. For each family, we compute the isomorphism type of the isogeny kernel and the dimension of the image of the family in the appropriate moduli space. The families are derived from Cassou--Nogu\`es and Couveignes' explicit classification of pairs (f,g) of polynomials such that f(x_1) - g(x_2) is reducible.
A majority coloring of a directed graph is a vertex coloring in which each vertex has the same color as at most half of its out-neighbors. In this note we simplify some proof techniques and generalize previously known results on various generalizations of majority coloring. In particular, our unified and simplified approach works for paintability - an on-line analog of the list coloring.
This paper has been withdrawn by the author. The paper has been accepted for publication in Communications on Pure and Applied Mathematics.
We investigate the surface Rashba effect for a surface of reduced in-plane symmetry. Formulating a k.p perturbation theory, we show that the Rashba splitting is anisotropic, in agreement with symmetry-based considerations. We show that the anisotropic Rashba splitting is due to the admixture of bulk states of different symmetry to the surface state, and it cannot be explained within the standard theoretical picture supposing just a normal-to-surface variation of the crystal potential. Performing relativistic ab initio calculations we find a remarkably large Rashba anisotropy for an unreconstructed Au(110) surface that is in the experimentally accessible range.
Context. Subdwarf B pulsators exhibit pressure (p) and/or gravity (g) modes. Their frequency spectra range from very simple, with few frequencies, to very rich, with more than fifty peaks in some cases. Balloon09 is a hybrid pulsating subdwarf B, showing a large number of p- and g-modes including a triplet and a quintuplet-like structures which are interpreted as p-mode frequency splittings due to stellar rotation. Photometric observations undertaken in two subsequent years revealed a change in these rotational splittings of 0.24 - 0.58 {\mu}Hz/yr. Aims. We analyse the possibility of angular momentum interchange between stellar rotation and internal gravity waves as a mechanism for the observed rotational splitting variations. Methods. The expected change in the rotational splitting of eigenmodes resulting from this mechanism are computed in the nonadiabatic linear approximation for a stellar structure model that is representative of the target star. The fact that g-modes are also observed in Balloon09 makes it a particularly suitable candidate for our study, because the change in the rotational splittings are proportional to the amplitude squared of the g-modes which, in this case, can be estimated from the observations. Results. We find that this mechanism is able to predict changes in the splittings that can be of the same order of magnitude as the observed variations.
Using an inclusion of one reflexive polytope into another is a well-known strategy for connecting the moduli spaces of two Calabi-Yau families. In this paper we look at the question of when an inclusion of reflexive polytopes determines a torically-defined extremal transition between smooth Calabi-Yau hypersurface families. We show this is always possible for reflexive polytopes in dimensions two and three. However, in dimension four and higher, obstructions can occur. This leads to a smooth projective family of Calabi-Yau threefolds that is birational to one of Batyrev's hypersurface families, but topologically distinct from all such families.
High resolution echelle spectra of PW And (HD~1405) have been taken during eight observing runs from 1999 to 2002. The detailed analysis of the spectra allow us to determine its spectral type (K2V), mean heliocentric radial velocity (V_hel = -11.15 km/s) rotational velocity (vsin{i} = 22.6 km/s), and equivalent width of the lithium line 6707.8 AA (EW(LiI) = 273 mAA). The kinematic (Galactic Velocity (U, V, W)) confirms its membership of the Local Association moving group, in agreement with the age (30 to 80 Myrs) inferred from the color magnitude diagram and the lithium equivalent width. Photospheric activity (presence of cool spots that disturb the profiles of the photospheric lines) has been detected as changes in the the bisectors of the cross correlation function (CCF) resulting of cross-correlate the spectra of PW And with the spectrum of a non active star of similar spectral type. These variations of the CCF bisectors are related to the variations in the measured radial velocities and are modulated with a period similar to the photometric period of the star. At the same time, chromospheric activity has been analyzed, using the spectral subtraction technique and simultaneous spectroscopic observations of the H_alpha, H_beta, NaI D_1 and D_2$, HeI D_3, MgI b triplet, CaII H&K, and CaII infrared triplet lines. A flare was observed during the last observing run of 2001, showing an enhancement in the observed chromospheric lines. A less powerful flare was observed on 2002 August 23. The variations of the chromospheric activity indicators seem to be related to the photospheric activity. A correlation between radial velocity, changes in the CCF bisectors and equivalent width of different chromospheric lines is observed with a different behaviour between epochs 1999, 2001 and 2002.
Stellar activity induced by active structures (eg, spots, faculae) is known to strongly impact the radial velocity time series. It then limits the detection of small planetary RV signals (eg, an Earth-mass planet in the habitable zone of a solar-like star). In previous papers, we studied the detectability of such planets around the Sun seen as an edge-on star. For that purpose, we computed the RV and photometric variations induced by solar magnetic activity, using all active structures observed over one entire cycle. Our goal is to perform similar studies on stars with different physical and geometrical properties. As a first step, we focus on Sun-like stars seen with various inclinations, and on estimating detection capabilities with forthcoming instruments. To do so, we first parameterize the solar active structures with the most realistic pattern so as to obtain results consistent with the observed ones. We simulate the growth, evolution and decay of solar spots, faculae and network, using parameters and empiric laws derived from solar observations and literature. We generate the corresponding structure lists over a full solar cycle. We then build the resulting spectra and deduce the RV and photometric variations for a `Sun' seen with various inclinations. The produced RV signal takes into account the photometric contribution of structures as well as the attenuation of the convective blueshift. The comparison between our simulated activity pattern and the observed one validates our model. We show that the inclination of the stellar rotation axis has a significant impact on the time series. RV long-term amplitudes as well as short-term jitters are significantly reduced when going from edge-on to pole-on configurations. Assuming spin-orbit alignment, the optimal configuration for planet detection is an inclined star (i~45{\deg}).
Temporal action detection (TAD) is a challenging task which aims to temporally localize and recognize the human action in untrimmed videos. Current mainstream one-stage TAD approaches localize and classify action proposals relying on pre-defined anchors, where the location and scale for action instances are set by designers. Obviously, such an anchor-based TAD method limits its generalization capability and will lead to performance degradation when videos contain rich action variation. In this study, we explore to remove the requirement of pre-defined anchors for TAD methods. A novel TAD model termed as Selective Receptive Field Network (SRF-Net) is developed, in which the location offsets and classification scores at each temporal location can be directly estimated in the feature map and SRF-Net is trained in an end-to-end manner. Innovatively, a building block called Selective Receptive Field Convolution (SRFC) is dedicatedly designed which is able to adaptively adjust its receptive field size according to multiple scales of input information at each temporal location in the feature map. Extensive experiments are conducted on the THUMOS14 dataset, and superior results are reported comparing to state-of-the-art TAD approaches.
The double graph of a graph $G$ is defined as $\mathcal{D}[G]$ = $G \times T_2$, where \(T_2\) is the total graph with 2 vertices and $\times$ stands for the Kronecker product of graphs. In this paper, sufficient conditions for double graphs to be maximum vertex-connected, maximum edge-connected are presented.
We generalize the second law of thermodynamics in its maximum work formulation for a nonequilibrium initial distribution. It is found that in an isothermal process, the Boltzmann relative entropy (H-function) is not just a Lyapunov function but also tells us the maximum work that may be gained from a nonequilibrium initial state. The generalized second law also gives a fundamental relation between work and information. It is valid even for a small Hamiltonian system not in contact with a heat reservoir but with an effective temperature determined by the isentropic condition. Our relation can be tested in the Szilard engine, which will be realized in the laboratory.
The YY Ori stars are T Tauri stars with prominent time-variable redshifted absorption components that flank certain emission lines. One of the brightest in this class is S CrA, a visual double star. We have obtained a series of high-resolution spectra of the two components during four nights with the UVES spectrograph at the Very Large Telescope. We followed the spectral changes occurring in S CrA to derive the physical structure of the accreting gas.   We found that both stars are very similar with regard to surface temperature, radius, and mass. Variable redshifted absorption components are particularly prominent in the SE component. During one night, this star developed a spectrum unique among the T Tauri stars: extremely strong and broad redshifted absorption components appeared in many lines of neutral and ionized metals, in addition to those of hydrogen and helium. The absorption depths of cooler, low ionization lines peak at low velocities - while more highly ionized lines have peak absorption depths at high velocities. The different line profiles indicate that the temperature and density of the accretion stream increase as material approaches the star. We derive the physical conditions of the flow at several points along the accretion funnel directly from the spectrum of the infalling gas. We estimated mass accretion rates of about 10^(-7) solar masses per year, which is similar to that derived from the relation based on the strength of H alpha emission line.   This is the first time the density and temperature distributions in accretion flows around a T Tauri star have been inferred from observations. Compared with predictions from standard models of accretion in T Tauri stars, which assume a dipole stellar magnetic field, we obtained higher densities and a steeper temperature rise toward the star.
We describe an image-based method that uses two radio criteria, compactness and spectral index, to identify promising pulsar candidates among Fermi Large Area Telescope (LAT) unassociated sources. These criteria are applied to those radio sources from the Giant Metrewave Radio Telescope all-sky survey at 150 MHz (TGSS ADR1) found within the error ellipses of unassociated sources from the 3FGL catalog and a preliminary source list based on 7 years of LAT data. After follow-up interferometric observations to identify extended or variable sources, a list of 16 compact, steep-spectrum candidates is generated. An ongoing search for pulsations in these candidates, in gamma rays and radio, has found six millisecond pulsars and one normal pulsar. A comparison of this method with existing selection criteria based on gamma-ray spectral and variability properties suggests that the pulsar discovery space using Fermi may be larger than previously thought. Radio imaging is a hitherto underutilized source selection method that can be used, as with other multi-wavelength techniques, in the search for Fermi pulsars.