ShantanuT01/DACTYL-Pretraining huggingface dataset:
Forthcoming cosmic microwave background (CMB) polarized anisotropy experiments have the potential to revolutionize our understanding of the Universe and fundamental physics. The sought-after, tale-telling signatures will be however distributed over voluminous data sets which these experiments will collect. These data sets will need to be efficiently processed and unwanted contributions due to astrophysical, environmental, and instrumental effects characterized and efficiently mitigated in order to uncover the signatures. This poses a significant challenge to data analysis methods, techniques, and software tools which will not only have to be able to cope with huge volumes of data but to do so with unprecedented precision driven by the demanding science goals posed for the new experiments. A keystone of efficient CMB data analysis are solvers of very large linear systems of equations. Such systems appear in very diverse contexts throughout CMB data analysis pipelines, however they typically display similar algebraic structures and can therefore be solved using similar numerical techniques. Linear systems arising in the so-called map-making problem are one of the most prominent and common ones. In this work we present a massively parallel, flexible and extensible framework, comprised of a numerical library, MIDAPACK, and a high level code, MAPPRAISER, which provide tools for solving efficiently such systems. The framework implements iterative solvers based on conjugate gradient techniques: enlarged and preconditioned using different preconditioners. We demonstrate the framework on simulated examples reflecting basic characteristics of the forthcoming data sets issued by ground-based and satellite-borne instruments, executing it on as many as 16,384 compute cores. The software is developed as an open source project freely available to the community at: https://github.com/B3Dcmb/midapack .
We study the de Rham fundamental group of the configuration space $E^{(n)}$ of $n+1$ marked points on an elliptic curve $E$, and define multiple elliptic polylogarithms. These are multivalued functions on $E^{(n)}$ with unipotent monodromy, and are constructed by a general averaging procedure.   We show that all iterated integrals on $E^{(n)}$, and in particular the periods of the unipotent fundamental group of the punctured curve $E \backslash \{0\}$, can be expressed in terms of these functions.
The onset and melting of locally staggered charge/orbital correlations is investigated within a two-orbital correlated electron model with inter-orbital and inter-site Coulomb interactions. Beyond the critical doping concentration x_c ~ 0.2, the (pi,pi,pi) staggered orbital order in the ferromagnet is found to be stabilized at finite temperature. The CE-type orbital correlation exhibits a sharp onset close to the Curie temperature and rapid thermal melting, which provides quantitative understanding of the (pi/2,pi/2,0) feature observed near T_c in neutron scattering experiments. In the zig-zag AF state, the CE-type orbital correlations are found to be even more readily stabilized, but only within a narrow doping regime around x=0.5.
We study electron transport through a domain wall in a ferromagnetic nanowire subject to spin-dependent scattering. A scattering matrix formalism is developed to address both coherent and incoherent transport properties. The coherent case corresponds to elastic scattering by static defects, which is dominant at low temperatures, while the incoherent case provides a phenomenological description of the inelastic scattering present in real physical systems at room temperature. It is found that disorder scattering increases the amount of spin-mixing of transmitted electrons, reducing the adiabaticity. This leads, in the incoherent case, to a reduction of conductance through the domain wall as compared to a uniformly magnetized region which is similar to the giant magnetoresistance effect. In the coherent case, a reduction of weak localization, together with a suppression of spin-reversing scattering amplitudes, leads to an enhancement of conductance due to the domain wall in the regime of strong disorder. The total effect of a domain wall on the conductance of a nanowire is studied by incorporating the disordered regions on either side of the wall. It is found that spin-dependent scattering in these regions increases the domain wall magnetoconductance as compared to the effect found by considering only the scattering inside the wall. This increase is most dramatic in the narrow wall limit, but remains significant for wide walls.
The fast growing deep learning technologies have become the main solution of many machine learning problems for medical image analysis. Deep convolution neural networks (CNNs), as one of the most important branch of the deep learning family, have been widely investigated for various computer-aided diagnosis tasks including long-term problems and continuously emerging new problems. Image contour detection is a fundamental but challenging task that has been studied for more than four decades. Recently, we have witnessed the significantly improved performance of contour detection thanks to the development of CNNs. Beyond purusing performance in existing natural image benchmarks, contour detection plays a particularly important role in medical image analysis. Segmenting various objects from radiology images or pathology images requires accurate detection of contours. However, some problems, such as discontinuity and shape constraints, are insufficiently studied in CNNs. It is necessary to clarify the challenges to encourage further exploration. The performance of CNN based contour detection relies on the state-of-the-art CNN architectures. Careful investigation of their design principles and motivations is critical and beneficial to contour detection. In this paper, we first review recent development of medical image contour detection and point out the current confronting challenges and problems. We discuss the development of general CNNs and their applications in image contours (or edges) detection. We compare those methods in detail, clarify their strengthens and weaknesses. Then we review their recent applications in medical image analysis and point out limitations, with the goal to light some potential directions in medical image analysis. We expect the paper to cover comprehensive technical ingredients of advanced CNNs to enrich the study in the medical image domain.
We present SkelNetOn 2019 Challenge and Deep Learning for Geometric Shape Understanding workshop to utilize existing and develop novel deep learning architectures for shape understanding. We observed that unlike traditional segmentation and detection tasks, geometry understanding is still a new area for deep learning techniques. SkelNetOn aims to bring together researchers from different domains to foster learning methods on global shape understanding tasks. We aim to improve and evaluate the state-of-the-art shape understanding approaches, and to serve as reference benchmarks for future research. Similar to other challenges in computer vision, SkelNetOn proposes three datasets and corresponding evaluation methodologies; all coherently bundled in three competitions with a dedicated workshop co-located with CVPR 2019 conference. In this paper, we describe and analyze characteristics of datasets, define the evaluation criteria of the public competitions, and provide baselines for each task.
We prove an interior regularity result for solutions of a purely integro-differential Bellman equation. This regularity is enough for the solutions to be understood in the classical sense. If we let the order of the equation approach two, we recover the theorem of Evans and Krylov about the regularity of solutions to concave uniformly elliptic partial differential equations.
We study some hybrid inverse problems associated to BVP's for Schr\"odinger and Helmholtz type equations. The inverse problems we consider consist in the determination of coefficients from the knowledge of internal energies. We establish local Lipschitz stability inequalities as well as conditional H\"older stability inequalities.
Ions, protons and possibly a small flux of electrons and positrons are accelerated outward from the polar cap of a normal or millisecond pulsar whose rotational spin is antiparallel with its magnetic moment. The Langmuir modes of this relativistic plasma have several properties of significance for the origin of coherent radio emission. The characteristics of the mode are determined by the sequence of singularities in the dielectric tensor at real angular frequencies, which in turn is fixed by the electron-positron momentum distribution. We find that under a certain condition on its momentum distribution, an electron-positron flux two orders of magnitude smaller than the Goldreich-Julian flux stabilizes the plasma and extinguishes the mode. But more generally, both the growth rate and wavenumber of the multi-component Langmuir mode can be as much as an order of magnitude larger than those of the two-component ion-proton mode. It appears to be a further effective source for the plasma turbulence whose decay is probably responsible for the observed emission.
E+A galaxies are believed to be a short phase connecting major merger ULIRGs with red and dead elliptical galaxies. Their optical spectrum suggests a massive starburst that was quenched abruptly, and their bulge-dominated morphologies with tidal tails suggest that they are merger remnants. AGN-driven winds are believed to be one of the processes responsible for the sudden quenching of star formation and for the expulsion and/or destruction of the remaining molecular gas. Little is known about AGN-driven winds in this short-lived phase. In this paper we present the first and unique sample of post starburst galaxy candidates with AGN that show indications of ionized outflows in their optical emission lines. Using IRAS-FIR observations, we study the star formation in these systems and find that many systems selected to have post starburst signatures in their optical spectrum are in fact obscured starbursts. Using SDSS spectroscopy, we study the stationary and outflowing ionized gas. We also detect neutral gas outflows in 40\% of the sources with mass outflow rates 10--100 times more massive than in the ionized phase. The mean mass outflow rate and kinetic power of the ionized outflows in our sample ($\dot{M}\sim 1\, \mathrm{M_{\odot}/yr}$, $\dot{E}\sim 10^{41}\, \mathrm{erg/sec}$) are larger than those derived for active galaxies of similar AGN luminosity and stellar mass. For the neutral outflow ($\dot{M}\sim 10\, \mathrm{M_{\odot}/yr}$, $\dot{E}\sim 10^{42}\, \mathrm{erg/sec}$), their mean is smaller than that observed in (U)LIRGs with and without AGN.
We show that the so called Robinson-Trautman-Maxwell equations do not constitute a well posed initial value problem. That is, the dependence of the solution on the initial data is not continuous in any norm built out from the initial data and a finite number of its derivatives. Thus, they can not be used to solve for solutions outside the analytic domain.
We study the spectral properties of a diffusion process taking place on the Internet network focusing on the slowest decaying modes. These modes allow us to identify an underlying modular structure of the Internet roughly corresponding to individual countries. For instance in the slowest decaying mode the diffusion current flows from Russia towards US military sites. These two regions thus constitute the extreme edges of the Internet. Quantitatively the modular structure of the Internet manifests itself in approximately 10 times larger participation ratio of its slow decaying modes compared to the null model - a random scale-free network. We propose to use the fraction of nodes participating in slow decaying modes as a general measure of the modularity of a network. For the 100 slowest decaying modes of the Internet we measured this fraction to be around 30%. Finally we suggest, that the degree of isolation of an individual module can be assessed by comparing its participation in different diffusion modes. Using the proportionality of response as a criterion we find that the independent module approximation works well for the Internet.
We present theoretical and experimental data on the magneto-optical contributions to the complex refractive index in the extreme ultraviolet (XUV) range covering the 3p resonances of Fe, Co, and Ni. Comparing the spectra from density functional theory with magnetic circular dichroism measurements we find that many body corrections and local field efects are of crucial importance for accurate description of the spectra. Our results are relevant for the application of static XUV spectroscopy for multi element magnetic systems as well as for the investigation of ultrafast magnetization dynamics.
Recently, Bradley studied partial sums of multiple q-zeta values and proved a duality result. In this paper, we present a generalization of his result.
The game of peg solitaire on graphs was introduced by Beeler and Hoilman in 2011. In this game, pegs are initially placed on all but one vertex of a graph $G$. If $xyz$ forms a path in $G$ and there are pegs on vertices $x$ and $y$ but not $z$, then a {\em jump} places a peg on $z$ and removes the pegs from $x$ and $y$. A graph is called solvable if, for some configuration of pegs occupying all but one vertex, some sequence of jumps leaves a single peg. We study the game of {\em reversible peg solitaire}, where there are again initially pegs on all but one vertex, but now both jumps and unjumps (the reversal of a jump) are allowed. We show that in this game all non-star graphs that contain a vertex of degree at least three are solvable, that cycles and paths on $n$ vertices, where $n$ is divisible by $2$ or $3$, are solvable, and that all other graphs are not solvable. We also classify the possible starting hole and ending peg positions for solvable graphs.
The Mixmaster dynamics is revisited in a new light as revealing a series of transitions in the complex scale invariant scalar invariant of the Weyl curvature tensor best represented by the speciality index $\mathcal{S}$, which gives a 4-dimensional measure of the evolution of the spacetime independent of all the 3-dimensional gauge-dependent variables except for the time used to parametrize it. Its graph versus time characterized by correlated isolated pulses in its real and imaginary parts corresponding to curvature wall collisions serves as a sort of electrocardiogram of the Mixmaster universe, with each such pulse pair arising from a single circuit or ``complex pulse'' around the origin in the complex plane. These pulses in the speciality index and their limiting points on the real axis seem to invariantly characterize some of the so called spike solutions in inhomogeneous cosmology and should play an important role as a gauge invariant lens through which to view current investigations of inhomogeneous Mixmaster dynamics.
We investigate experimentally the capacitive coupling between a two-electron spin qubit and flying electrons propagating in quantum Hall edge channels. We demonstrate that the qubit is an ultrasensitive and fast charge detector with the potential to allow single shot detection of a single flying electron. This work opens the route towards quantum electron optics at the single electron level above the Fermi sea.
We report the results of a study of the di erential magnetic susceptibility of Sr3Ru2O7 as a function of temperature and magnetic elds applied at a series of angles to the ab plane. By analysing the real and imaginary parts of the susceptibility, we conclude that the eld angle acts as a continuous tuning parameter for the critical end-point to a line of rst order metamagnetic phase transitions. The end-point sits at approximately 1.25K for elds applied in the ab plane, and is depressed to below 50 mK when the eld is aligned within 10 of the c axis.
Transient surveys have recently discovered a class of supernovae (SNe) with extremely rapidly declining light curves. These events are also often relatively faint, especially compared to Type Ia SNe. The common explanation for these events involves a weak explosion, producing a radioactive outflow with small ejected mass and kinetic energy (M ~ 0.1 Msun and E ~ 0.1 B, respectively), perhaps from the detonation of a helium shell on a white dwarf. We argue, in contrast, that these events may be Type Ib/c SNe with typical masses and energies (M ~ 3 Msun, E ~ 1 B), but which ejected very little radioactive material. In our picture, the light curve is powered by the diffusion of thermal energy deposited by the explosion shock wave, and the rapid evolution is due to recombination, which reduces the opacity and results in an "oxygen-plateau" light curve. Using a radiative transfer code, we generate synthetic spectra and light curves and demonstrate that this model can reasonably fit the observations of one event, SN 2010X. Similar models may explain the features of other rapidly evolving SNe such as SN 2002bj and SN 2005ek. SNe such as these require stripped-envelope progenitors with rather large radii (R ~ 20 Rsun), which may originate from a mass loss episode occurring just prior to explosion.
Topological insulating phases are primarily associated with condensed-matter systems, which typically feature short-range interactions. Nevertheless, many realizations of quantum matter can exhibit long-range interactions, and it is still largely unknown the effect that these latter may exert upon the topological phases. In this Letter, we investigate the Su-Schrieffer-Heeger topological insulator in the presence of long-range interactions. We show that this model can be readily realized in quantum simulators with trapped ions by means of a periodic driving. Our results indicate that the localization of the associated edge states is enhanced by the long-range interactions, and that the localized components survive within the ground state of the model. These effects could be easily confirmed in current state-of-the-art experimental implementations.
We prove that every simplicial complex is the dual complex of some simple normal crossing divisor in a smooth variety. As an application, we simplify and extend the results of Kapovich--Koll\'ar (math.AG:1109.4047) on the existence of singularities with given dual complex.
When the contacts of an open system flip between different reservoirs, the resulting nonequilibrium shows increased dynamical activity. We investigate such active gating for one-dimensional symmetric (SEP) and asymmetric (ASEP) exclusion models where the left/right boundary rates for entrance and exit of particles are exchanged at random times. Such rocking makes SEP spatially symmetric and on average there is no boundary driving; yet the entropy production increases in the rocking rate. For ASEP a non-monotone density profile can be obtained with particles clustering at the edges. In the totally asymmetric case, there is a bulk transition to a maximal current phase as the rocking exceeds a finite threshold, depending on the boundary rates. We study the resulting density profiles and current as functions of the rocking rate.
We study the asymmetric exclusion process on a regular Cayley tree with arbitrary co-ordination number. In this model particles can enter the system only at the parent site and exit from one of the sites at the last level. In the bulk they move from the occupied sites to one of their unoccupied downward neighbours, chosen randomly. We show that the steady state current that flow from one level to the next is independent of the exit rate, and increase monotonically with the entry rate and the co-ordination number. Unlike TASEP, the model has only one phase and the density profile show no boundary layers. We argue that in blood, air or water circulations systems branching is essential to maintain a free flow within the system which is independent of exit rates.
Static, spherically symmetric, traversable wormhole solutions with electric or magnetic charges are shown to exist in general relativity in the presence of scalar fields nonminimally coupled to gravity. These wormholes, however, turn out to be unstable under spherically symmetric perturbations. The instability is related to blowing-up of the effective gravitational constant on a certain sphere.
We consider a service system model primarily motivated by the problem of efficient assignment of virtual machines to physical host machines in a network cloud, so that the number of occupied hosts is minimized.   There are multiple types of arriving customers, where a customer's mean service time depends on its type. There is an infinite number of servers. Multiple customers can be placed for service into one server, subject to general "packing" constraints. Service times of different customers are independent, even if served simultaneously by the same server. Each new arriving customer is placed for service immediately, either into a server already serving other customers (as long as packing constraints are not violated) or into an idle server. After a service completion, each customer leaves its server and the system.   We propose an extremely simple and easily implementable customer placement algorithm, called Greedy-Random (GRAND). It places each arriving customer uniformly at random into either one of the already occupied servers (subject to packing constraints) or one of the so-called zero-servers, which are empty servers designated to be available to new arrivals. One instance of GRAND, called GRAND($aZ$), where $a\ge 0$ is a parameter, is such that the number of zero-servers at any given time $t$ is $aZ(t)$, where $Z(t)$ is the current total number of customers in the system. We prove that GRAND($aZ$) with $a>0$ is asymptotically optimal, as the customer arrival rates grow to infinity and $a\to 0$, in the sense of minimizing the total number of occupied servers in steady state. In addition, we study by simulations various versions of GRAND and observe the dependence of convergence speed and steady-state performance on the number of zero-servers.
We report the nanodiamond-derived onion-like carbon successfully applied as an electrocatalyst for [VO]2+/[VO2]+ redox flow battery, as drop-coated (in the as-synthesized state) on glassy carbon or carbon felt electrodes. We show that its reversibility and catalytic activity in its as-synthesized state was comparable to some of the best data in the literature which employed surface modifications. We clarified the origin of such excellent performances by physical/electrochemical analyses.
The effect of the pulse-shape on pump-probe spectroscopies is examined for the simplest model of noninteracting fermions on an infinite-dimensional hypercubic lattice. The probe-modified density of states follows the time evolution of the pump and displays narrowing and Floquet-like sidebands at the pump maximum, whereas the photoelectron spectra are also strongly affected by the nonequilibrium occupation of the single-particle states due to the excitation from the pump. The nonequilibrium Raman cross section is derived, and the nonresonant one in both the $A_{1\mathrm{g}}$ and $B_{1\mathrm{g}}$ symmetries contains a number of peaks at the pump maximum, which can be attributed to an interference effect or Brillouin scattering off the time variations of the stress tensor. Both the "measured" occupation of single-particle states and the ratio of Stokes to anti-Stokes peaks are strongly modified by the probe-pulse width, which must be included in the interpretation of experimental results.