ShantanuT01/DACTYL-Pretraining huggingface dataset:
Recently observed rare heavy ion fusion processes, where the entire available energy is carried away by a single pion, is an example of extreme collectivity in nuclear reactions. We calculate the cross section in the approximation of sudden overlap, modeling the initial and final nuclei by moving harmonic oscillator potentials. This allows for a fully quantum-mechanical treatment, exact conservation of linear and angular momenta and fulfillment of the Pauli principle. The results are in satisfactory agreement with data. Mass number dependence and general trends of the process are discussed.
We show how to view the standard Follow-the-Leader (FtL) model as a numerical method to compute numerically the solution of the Lighthill--Whitham--Richards (LWR) model for traffic flow. As a result we offer a simple proof that FtL models converge to the LWR model for traffic flow when traffic becomes dense. The proof is based on techniques used in the analysis of numerical schemes for conservation laws, and the equivalence of weak entropy solutions of conservation laws in the Lagrangian and Eulerian formulation.
We propose a different route to time-reversal invariant Weyl semimetals employing multilayer heterostructures comprising ordinary "trivial" insulators and nontrivial insulators with \textit{pairs} of protected Dirac cones on the surface. We consider both the case of weak topological insualtors, where surface Dirac cones are pinned to time-reversal invariant momenta, and of topological crystalline insulators with unpinned surface Dirac cones. For both realizations we explain phenomenologically how the proposed construction leads to the emergence of a Weyl semimetal phase. We further formulate effective low-energy models for which we prove the existence of semimetallic phases with four isolated Weyl points. Finally, we discuss how the proposed design can be realized experimentally with state-of-the-art technologies.
We establish a general formula for the Laplace transform of the hitting times of a Gaussian process. Some consequences are derived, and particular cases like the fractional Brownian motion are discussed.
We consider supercritical accretion onto a compact object when the accretion rate exceeds its value derived from the Eddington limit: L_{Edd}/c^2. We use the scenario that was proposed by Shakura and Sunyaev (1973) for the supercritical regime, according to which matter flows out of the gas-disk surface under radiation pressure. An analytic solution of the accretion-disk structure is obtained for this scenario by using classical equations. An attempt is made to construct a model for nonconservative supercritical accretion with advection. To this end, we develop a numerical scheme for calculating the structure of an advective disk with mass outflow. The goal of solving the problem of a supercritical disk with mass loss is to explain accreting sources with outflowing envelopes, for example, SS 433 and galactic nuclei. The structure and observational manifestations of the envelope which forms around a supercritical disk are considered by taking into account bremsstrahlung absorption and Thomson scattering of photons.
Magnetic competition in topological kagome magnets is studied by incorporating the spin-orbit coupling, the anisotropic Hund coupling and spin exchange into the kagome lattice. Using the Bogoliubov variational principle we find the stable phases at zero and finite temperatures. At zero temperature and in the strong Ising-Hund coupling regime, a magnetic tunability from the out-of-plane ferromagnetism (FM) to the in-plane antiferromagnetism (AFM) is achieved by a universal property of the critical in-plane Hund coupling. At two-thirds filling the phase transition from the out-of-plane FM to the in-plane AFM is accompanied by a topological transition from quantum anomalous Hall (QAH) to quantum anomalous spin Hall (QASH) effect. Nearby half filling a large anomalous Hall conductance is observed at the magnetic phase transition. At finite temperature the out-of-plane FM is stable until a crossing temperature, above which the in-plane AFM is stable, but the out-of-plane FM magnetization is still finite. This suggests a coexistence of these magnetic phases in a finite temperature range.
It is more subtle to obtain the chiral vortical effect (CVE) than chiral magnetic effect (CME) in quantum transport approach. To investigate the subtlty of the CVE we present two different derivation in the Wigner function approach. The first one is based on the method in our previous work \cite{Gao:2012ix} in which the CVE was derived under static-equilibrium conditions without details. We provide a detailed derivation using a more transparent and powerful method, which can be easily generalized to higher order calculation. In this derivation of the CVE current, there is an explicit Lorentz covariance. The second derivation is based on a more general chiral kinetic theory in a semi-classical expansion of the Wigner function without assuming static-equilibrium conditions \cite{Gao:2018wmr}. In this derivation, there is a freedom to choose a reference frame for the CVE current, so the explicit Lorentz covariance seems to be lost. Howerver, under static-equilibrium conditions, we show that the CVE current in this derivation can be decomposed into two parts, identified as the normal and magnetization current. Each part depends on the reference frame, but the sum of two parts does give the total CVE current which is independent of the reference frame. In the comoving frame of the fluid, it can be shown that the normal and magnetization current give one-third and two-thirds of the total CVE current respectively. This gives a natural solution to the 'one-third' puzzle in the CVE current in three-dimensional version of the chiral kinetic theory in the literature.
We are interested in the dynamic of a structured branching population where the trait of each individual moves according to a Markov process. The rate of division of each individual is a function of its trait and when a branching event occurs, the trait of a descendant at birth depends on the trait of the mother. We prove a law of large numbers for the empirical distribution of ancestral trajectories. It ensures that the empirical measure converges to the mean value of the spine which is a time-inhomogeneous Markov process describing the trait of a typical individual along its ancestral lineage. Our approach relies on ergodicity arguments for this time-inhomogeneous Markov process. We apply this technique on the example of a size-structured population with exponential growth in varying environment.
We predict the electromagnetic field driven nucleation of nanoparticles that provide plasmonic oscillations in resonance with the field frequency. The oscillations assume a phase that maximizes the particle polarization and energy gain due to nucleation. We derive closed form expressions for the corresponding nucleation barrier and particle shape vs. field frequency and strength, metal plasma frequency, conductivity, and the host dielectric permittivity. We show that the plasmonic polarization allows for nucleation of particles that would not be stable in zero field.
We characterize the symmetric measures which satisfy the one dimensional convex Poincar\'e inequality. For these measures the tenesorization argument yields concentration inequalities for their products and convex sets in R^n.
In this paper, we prove a new type of energy estimates for the compressible Euler's equation with free boundary, with a boundary part and an interior part. These can be thought of as a generalization of the energies in Christodoulou and Lindblad [CL] to the compressible case and do not require the fluid to be irrotational. In addition, we show that our estimates are in fact uniform in the sound speed. As a consequence, we obtain convergence of solutions of compressible Euler equations with a free boundary to solutions of the incompressible equations, generalizing the result of Ebin [Eb] to when you have a free boundary. In the incompressible case our energies reduces to those in [CL] and our proof in particular gives a simplified proof of the estimates in [CL] with improved error estimates. Since for an incompressible irrotational liquid with free surface there are small data global existence results our result leaves open the possibility of long time existence also for slightly compressible liquids with a free surface.
Due to its unique long-term coverage and high photometric precision, observations from the Kepler asteroseismic investigation will provide us with the possibility to sound stellar cycles in a number of solar-type stars with asteroseismology. By comparing these measurements with conventional ground-based chromospheric activity measurements we might be able to increase our understanding of the relation between the chromospheric changes and the changes in the eigenmodes.   In parallel with the Kepler observations we have therefore started a programme at the Nordic Optical Telescope to observe and monitor chromospheric activity in the stars that are most likely to be selected for observations for the whole satellite mission. The ground-based observations presented here can be used both to guide the selection of the special Kepler targets and as the first step in a monitoring programme for stellar cycles. Also, the chromospheric activity measurements obtained from the ground-based observations can be compared with stellar parameters such as ages and rotation in order to improve stellar evolution models.
The game in which acts of participants don't have an adequate description in terms of Boolean logic and classical theory of probabilities is considered. The model of the game interaction is constructed on the basis of a non-distributive orthocomplemented lattice. Mixed strategies of the participants are calculated by the use of probability amplitudes according to the rules of quantum mechanics. A scheme of quantization of the payoff function is proposed and an algorithm for the search of Nash equilibrium is given. It is shown that differently from the classical case in the quantum situation a discrete set of equilibrium is possible.
Defect formation in LiF, which is used as an observation window in ramp and shock experi- ments, has significant effects on its transmission properties. Given the extreme conditions of the experiments it is hard to measure the change in transmission directly. Using molecular dynam- ics, we estimate the change in conductivity as a function of the concentration of likely point and extended defects using a Green-Kubo technique with careful treatment of size-effects. With this data, we form a model of the mean behavior and its estimated error; then, we use this model to predict the conductivity of a large sample of defective LiF resulting from a direct simulation of ramp compression as a demonstration of the accuracy of its predictions. Given estimates of defect densities in a LiF window used in an experiment, the model can be used to correct the observations of thermal energy through the window. In addition, the methodology we develop is extensible to modelling, with quantified uncertainty, the effects of a variety of defects on thermal conductivity of solid materials.
The chromatic polynomial $P(G,x)$ of a graph $G$ of order $n$ can be expressed as $\sum\limits_{i=1}^n(-1)^{n-i}a_{i}x^i$, where $a_i$ is interpreted as the number of broken-cycle free spanning subgraphs of $G$ with exactly $i$ components. The parameter $\epsilon(G)=\sum\limits_{i=1}^n (n-i)a_i/\sum\limits_{i=1}^n a_i$ is the mean size of a broken-cycle-free spanning subgraph of $G$. In this article, we confirm and strengthen a conjecture proposed by Lundow and Markstr\"{o}m in 2006 that $\epsilon(T_n)< \epsilon(G)<\epsilon(K_n)$ holds for any connected graph $G$ of order $n$ which is neither the complete graph $K_n$ nor a tree $T_n$ of order $n$. The most crucial step of our proof is to obtain the interpretation of all $a_i$'s by the number of acyclic orientations of $G$.
The XY-pyrochlore antiferromagnet \ETO\ is studied by heat capacity measurements and electron spin resonance spectroscopy performed on single crystal samples. The magnetic phase diagrams are established for two directions of applied field, $H\parallel [100]$ and $H\parallel [111]$. In the magnetically ordered phase observed below $T_N=1.2$ K, the magnetic excitation spectrum consists of a Goldstone mode acquiring an isotropic gap in an applied field, and another mode with a gap softening in the vicinity of a field-induced phase transition. This second-order transition takes place at a critical field $H_c$ above which the magnetization process is accompanied by a canting of the magnetic moments off their local "easy-planes". The specific heat curves for $H\parallel [100]$ ($H\gg H_c$) are well described by a model presuming a single dispersionless excitation mode with the energy gap obtained from the spectroscopic measurements.
We report the discovery of two Black Widow millisecond pulsars in the globular cluster M28 with the MeerKAT telescope. PSR J1824$-$2452M (M28M) is a 4.78-ms pulsar in a $5.82\,$hour orbit and PSR J1824$-$2452N (M28N) is a 3.35-ms pulsar in a $4.76\,$hour orbit. Both pulsars have dispersion measures near $119.30\,$pc$\,$cm$^{-3}$ and have low mass companion stars ($\sim$$0.01-0.03\,$M$_\odot$), which do not cause strong radio eclipses or orbital variations. Including these systems, there are now five known black widow pulsars in M28. The pulsar searches were conducted as a part of an initial phase of MeerKAT's globular cluster census (within the TRAPUM Large Survey Project). These faint discoveries demonstrate the advantages of MeerKAT's survey sensitivity over previous searches and we expect to find additional pulsars in continued searches of this cluster.
Motivated by a common Mathematical Finance topic, we discuss the reciprocal of the exit time from a cone of planar Brownian motion which also corresponds to the exponential functional of an associated Brownian motion. We prove a conjecture by Vakeroudis and Yor (2012) concerning infinite divisibility properties of this random variable and we present a novel simple proof of De Blassie's result (1987-1988) about the asymptotic behaviour of the distribution of the Bessel clock appearing in the skew-product representation of planar Brownian motion, for t large. Similar issues for the exponential functional of a Levy process are also discussed. We finally use the findings obtained by the windings approach in order to get results for quantities associated to the pricing of Asian options.
Ionic migration has been proposed as a possible cause of photovoltaic current-voltage hysteresis in hybrid perovskite solar cells. However, a major objection to this hypothesis is that hysteresis can be reduced by changing the interfacial contact materials, which are unlikely to significantly influence the behaviour of ionic defects within the perovskite phase. Here we use transient optoelectronic measurements, combined with device simulations, to show that the primary effects of ionic migration can in fact be observed both in devices with hysteresis, and with hysteresis free type contact materials. The data indicate that electric-field screening, consistent with ionic migration, is similar or identical in both high and low hysteresis CH3NH3PbI3 cells. Simulation of the transients shows that hysteresis requires the combination of both mobile ionic charge and recombination near the contacts. Passivating contact recombination results in higher photogenerated charge concentrations at forward bias which screen the ionic charge, reducing hysteresis.
We introduce three space-times that are discrete in time and compatible with the Lorentz symmetry. We show that these spaces are no commutative, with commutation relations similar to the relations of the Snyder and Yang spaces. Furthermore, using a reparametrized relativistic particle we obtain a realization of the Snyder type spaces and we construct an action for them.
Image alignment by mesh warps, such as meshflow, is a fundamental task which has been widely applied in various vision applications(e.g., multi-frame HDR/denoising, video stabilization). Traditional mesh warp methods detect and match image features, where the quality of alignment highly depends on the quality of image features. However, the image features are not robust in occurrence of low-texture and low-light scenes. Deep homography methods, on the other hand, are free from such problem by learning deep features for robust performance. However, a homography is limited to plane motions. In this work, we present a deep meshflow motion model, which takes two images as input and output a sparse motion field with motions located at mesh vertexes. The deep meshflow enjoys the merics of meshflow that can describe nonlinear motions while also shares advantage of deep homography that is robust against challenging textureless scenarios. In particular, a new unsupervised network structure is presented with content-adaptive capability. On one hand, the image content that cannot be aligned under mesh representation are rejected by our learned mask, similar to the RANSAC procedure. On the other hand, we learn multiple mesh resolutions, combining to a non-uniform mesh division. Moreover, a comprehensive dataset is presented, covering various scenes for training and testing. The comparison between both traditional mesh warp methods and deep based methods show the effectiveness of our deep meshflow motion model.
We present a photometric study of the early-type dwarf galaxy population of the Centaurus cluster, aiming at investigating the galaxy luminosity function (LF) and galaxy scaling relations down to the regime of galaxies with M_V~-10 mag. On deep VLT/FORS1 V- and I-band images of the central part of the cluster, we identify cluster dwarf-galaxy candidates using both morphological and surface brightness selection criteria. Photometric and structural parameters of the candidates are derived from analysis of their surface brightness profiles. Fundamental scaling relations, such as the colour-magnitude and the magnitude-surface brightness relation, are used to distinguish the cluster from the background. We find a flat LF with a slope of \alpha = -1.14 \pm 0.12 for M_V>-14 mag, when fitting a power law to the completeness-corrected galaxy number counts. When plotting the central surface brightness of a Sersic model vs. the galaxy magnitude, we find a continuous relation for magnitudes -20<M_V<-10 mag, with only the brightest core galaxies deviating from this relation, in agreement with previous studies of other clusters. In a size-luminosity diagram of early-type galaxies from a range of environments, we observe that R_eff slowly decreases with decreasing luminosity for -21<M_V<-13 mag and decreases more rapidly at fainter magnitudes. This trend continues to the ultra-faint Local Group dwarf galaxies (M_V~-4 mag). The continuous central surface brightness vs. absolute magnitude relation and the smooth relation in the size-luminosity diagram over a wide range of magnitudes are consistent with the interpretation of dwarf galaxies and more massive elliptical galaxies being one family of objects with gradually changing structural properties. The most massive core galaxies and the rare cE galaxies are the only exceptions.
Giant X-ray outbursts, with luminosities of about $ 10^{37}$ erg s$^{-1}$, are observed roughly every 5 years from the nearby Be/pulsar binary 1A 0535+262. In this article, we present observations of the source with VERITAS at very-high energies (VHE; E$>$100 GeV) triggered by the X-ray outburst in December 2009. The observations started shortly after the onset of the outburst, and they provided comprehensive coverage of the episode, as well as the 111-day binary orbit. No VHE emission is evident at any time. We also examined data from the contemporaneous observations of 1A 0535+262 with the Fermi/LAT at high energy photons (HE; E$>$0.1 GeV) and failed to detect the source at GeV energies. The X-ray continua measured with the Swift/XRT and the RXTE/PCA can be well described by the combination of blackbody and Comptonized emission from thermal electrons. Therefore, the gamma-ray and X-ray observations suggest the absence of a significant population of non-thermal particles in the system. This distinguishes 1A~0535+262 from those Be X-ray binaries (such as PSR B1259--63 and LS I +61$^{\circ}$303) that have been detected at GeV--TeV energies. We discuss the implications of the results on theoretical models.
In this work we study the smoothing effect of rough differential equations driven by a fractional Brownian motion with parameter $H>1/4$. The regularization estimates we obtain generalize to the fractional Brownian motion previous results by Kusuoka and Stroock and can be seen as a quantitative version of the existence of smooth densities under H\"ormander's type conditions.
We investigate the gas mass function of clusters of galaxies to measure the density fluctuation spectrum on cluster scales. The baryon abundance confined in rich clusters is computed from the gas mass function and compared with the mean baryon density in the universe which is predicted by the Big Bang Nucleosynthesis. This baryon fraction and the slope of the gas mass function put constraints on $\sigma_8$, the rms linear fluctuation on scales of $8h^{-1}\Mpc$, and the slope of the fluctuation spectrum, where $h$ is the Hubble constant in units of 100 $\kms \oMpc$. We find $\sigma_8 = 0.80 \pm 0.15$ and $n \sim -1.5$ for $0.5 \le h \le 0.8$, where we assume that the density spectrum is approximated by a power law on cluster scales: $\sigma(r) \propto r^{-{3+n\over{2}}}$. Our value of $\sigma_8$ is independent of the density parameter, $\Omega_0$, and thus we can estimate $\Omega_0$ by combining $\sigma_8$ obtained in this study with those from $\Omega_0$-dependent analyses to date. We find that $\sigma_8(\Omega_0)$ derived from the cluster abundance such as the temperature function gives $\Omega_0 \sim 0.5$ while $\sigma_8(\Omega_0)$ measured from the peculiar velocity field of galaxies gives $\Omega_0 \sim 0.2-1$, depending on the technique used to analyze peculiar velocity data. Constraints are also derived for open, spatially flat, and tilted Cold Dark Matter models and for Cold + Hot Dark Matter models.
We consider the gravity field of a Bose-Einstein condensate in a quantum superposition. The gravity field then is also in a quantum superposition which is in principle observable. Hence we have ``quantum gravity'' far away from the so-called Planck scale.
It is shown that the renormalized nuclear deformations in different mass regions can be globally scaled by two probability partition factors of Boltzmann-like distribution, which are derived from the competing valence $np$ and like-nucleon interactions. The partition factors are simply related to the probabilities of anti-parallel and fully-aligned orientations of the angular momenta of the neutrons and protons in the valence $np$ pairs, responsible for spherical- and deformed-shape phases, respectively. The partition factors derived from the renormalized deformations are also present in the new scaling law for the energies of the first $2^+$ states. A striking concordance between the distributions of the renormalized deformations and of the newly introduced parameter for the energies of the first $2^+$ states over the extended mass region from Ge to Cf is achieved, giving strong support to the existence of two phases: anti-aligned and fully-aligned subsets of $np$ pairs.