ShantanuT01/DACTYL-Pretraining huggingface dataset:
Re-based double perovskites (DPs) exhibit a complex interplay of structural and metal-insulator transitions. Here we systematically study the ground state electronic and structural properties for a family of Re-based DPs $A_2B$ReO$_6$ ($A$=Sr, Ca and $B$=Cr, Fe), which are related by a common low energy Hamiltonian, using density functional theory + $U$ calculations. We show that the on-site interaction $U$ of Re induces orbital ordering (denoted COO), with each Re site having an occupied $d_{xy}$ orbital and a C-type alternation among $d_{xz}/d_{yz}$, resulting in an insulating state consistent with experimentally determined insulators Sr$_2$CrReO$_6$, Ca$_2$CrReO$_6$, and Ca$_2$FeReO$_6$. The threshold value of $U_{Re}$ for orbital ordering is reduced by inducing $E_g$ octahedral distortions of the same C-type wavelength (denoted COD), which serves as a structural signature of the orbital ordering; octahedral tilting also reduces the threshold. The COO, and the concomitant COD, are a spontaneously broken symmetry for the Sr based materials (i.e. $a^0a^0c^-$ tilt pattern), while not for the Ca based systems (i.e. $a^-a^-b^+$ tilt pattern). Spin-orbit coupling does not qualitatively change the physics of the COO/COD, but can induce relevant quantitative changes. We prove that a single set of $U_{Cr}$,$U_{Fe}$,$U_{Re}$ capture the experimentally observed metallic state in Sr$_2$FeReO$_6$ and insulating states in the other three systems. We predict that the COO is the origin of the insulating state in Sr$_2$CrReO$_6$, and that the concomitant COD may be experimentally observed at sufficiently low temperatures (ie. space group P$4_2/m$). Additionally, given our prescribed values of $U$, we show that the COO induced insulating state in Ca$_2$CrReO$_6$ will survive even if the COD amplitude is suppressed (e.g. due to thermal fluctuations).
Given a finite transitive permutation group $G\leq \operatorname{Sym}(\Omega)$, with $|\Omega|\geq 2$, the derangement graph $\Gamma_G$ of $G$ is the Cayley graph $\operatorname{Cay}(G,\operatorname{Der}(G))$, where $\operatorname{Der}(G)$ is the set of all derangements of $G$. Meagher et al. [On triangles in derangement graphs, {\it J. Combin. Theory Ser. A}, 180:105390, 2021] recently proved that $\operatorname{Sym}(2)$ acting on $\{1,2\}$ is the only transitive group whose derangement graph is bipartite and any transitive group of degree at least three has a triangle in its derangement graph. They also showed that there exist transitive groups whose derangement graphs are complete multipartite.   This paper gives two new families of transitive groups with complete multipartite derangement graphs. In addition, we prove that if $p$ is an odd prime and $G$ is a transitive group of degree $2p$, then the independence number of $\Gamma_{G}$ is at most twice the size of a point-stabilizer of $G$.
Aims. We investigate the properties of the host galaxy of the blazar J0324+3410 (B2 0321+33) by the analysis of B and R images obtained with the NOT under good photometric conditions. Methods: The galaxy was studied using different methods: Sersic model fitting, unsharp-masked images, B-R image and B-R profile analysis. Results: The images show that the host galaxy has a ring-like morphology. The B-R colour image reveals two bluish zones: one that coincides with the nuclear region, interpreted as the signature of emission related to the active nucleus, the other zone is extended and is located in the host ring-structure. We discuss the hypothesis that the later is thermal emission from a burst of star formation triggered by an interacting/merging process.
We compare the standard 50%-efficient single beam splitter method for Bell-state measurement to a proposed 75%-efficient auxiliary-photon-enhanced scheme [W. P. Grice, Phys. Rev. A 84, 042331 (2011)] in light of realistic conditions. The two schemes are compared with consideration for high input state photon loss, auxiliary state photon loss, detector inefficiency and coupling loss, detector dark counts, and non-number-resolving detectors. We also analyze the two schemes when multiplexed arrays of non-number-resolving detectors are used. Furthermore, we explore the possibility of utilizing spontaneous parametric down-conversion as the auxiliary photon pair source required by the enhanced scheme. In these different cases, we determine the bounds on the detector parameters at which the enhanced scheme becomes superior to the standard scheme and describe the impact of the different imperfections on measurement success rate and discrimination fidelity. This is done using a combination of numeric and analytic techniques. For many of the cases discussed, the size of the Hilbert space and the number of measurement outcomes can be very large, which makes direct numerical solutions computationally costly. To alleviate this problem, all of our numerical computations are performed using pure states. This requires tracking the loss modes until measurement and treating dark counts as variations on measurement outcomes rather than modifications to the state itself. In addition, we provide approximate analytic expressions that illustrate the effect of different imperfections on the Bell-state analyzer quality.
When $k$ factors each taking one of $v$ levels may affect the correctness or performance of a complex system, a test is selected by setting each factor to one of its levels and determining whether the system functions as expected (passes the test) or not (fails). In our setting, each test failure can be attributed to at least one faulty (factor, level) pair. A nonadaptive test suite is a selection of such tests to be executed in parallel. One goal is to minimize the number of tests in a test suite from which we can determine which (factor, level) pairs are faulty, if any. In this paper, we determine the number of tests needed to locate faults when exactly one (or at most one) pair is faulty. To do this, we address an equivalent problem, to determine how many set partitions of a set of size $N$ exist in which each partition contains $v$ classes and no two classes in the partitions are equal.
Graphical elements: particularly tables and figures contain a visual summary of the most valuable information contained in a document. Therefore, localization of such graphical objects in the document images is the initial step to understand the content of such graphical objects or document images. In this paper, we present a novel end-to-end trainable deep learning based framework to localize graphical objects in the document images called as Graphical Object Detection (GOD). Our framework is data-driven and does not require any heuristics or meta-data to locate graphical objects in the document images. The GOD explores the concept of transfer learning and domain adaptation to handle scarcity of labeled training images for graphical object detection task in the document images. Performance analysis carried out on the various public benchmark data sets: ICDAR-2013, ICDAR-POD2017,and UNLV shows that our model yields promising results as compared to state-of-the-art techniques.
We present VLT-UVES echelle spectra of the Lyman alpha emission and absorption in five radio galaxies at redshifts z=2.55-4.1. Together with data from our pilot study, we have a sample of 7 such systems with radio source sizes ~ 1-90 kpc with which to address the origin of the absorbing gas. Echelle resolution again reveals that some systems with N_HI>1E18 cm^-2 in lower resolution data in fact consist of several weaker absorbers with N_HI<1E15 cm^-2. We identify two groups of HI absorbers: strong absorbers with N_HI=1E18-1E20 cm^-2 and weaker systems with N_HI=1E13-1E15 cm^-2. There are none at intermediate N_HI.   The strong absorbers may be a by-product of massive galaxy formation or could instead represent material cooling behind the expanding bow-shock of the radio jet, as simulated by Krause. New observations are required to discriminate between these possibilities. We argue that the weaker absorbers with N_HI=1E13-1E15 cm^-2 are part of the Lyman alpha forest, as their rate of incidence is within a factor of 2-4 of that in the IGM at large. Such column densities are consistent with models of a multi-phase proto-intracluster medium at z>2.
Entangled photons are crucial for quantum technologies, but generating arbitrary entangled photon states deterministically, efficiently, and with high fidelity remains a challenge. Here, we demonstrate how hybridization and dipole-dipole interactions -- potentially simultaneously available in colloidal quantum dots and molecular aggregates -- leveraged in conjunction can couple simple, well understood emitters into composite emitters with flexible control over the level structure. We show that cascade decay through carefully designed level structures can result in emission of frequency-entangled photons with Bell states and three-photon GHZ states as example cases. These results pave the way toward rational design of quantum optical emitters of arbitrarily entangled photons.
We present the results of an exact diagonalization study of the spin-1/2 Heisenberg antiferromagnet on a two-dimensional version of the pyrochlore lattice, also known as the square lattice with crossings or the checkerboard lattice. Examining the low energy spectra for systems of up to 24 spins, we find that all clusters studied have non-degenerate ground states with total spin zero, and big energy gaps to states with higher total spin. We also find a large number of non-magnetic excitations at energies within this spin gap. Spin-spin and spin-Peierls correlation functions appear to be short-ranged, and we suggest that the ground state is a spin liquid.
The lattice parameters, lattice stability and phonon dispersion curves of five proposed phases of Ti: alpha, beta, gamma, delta and omega are investigated within DFT. It is found that the sequence of high pressure phases at zero temperature is alpha, omega, gamma, delta and beta with the delta and beta phases becoming degenerate at high pressure. However, the gamma phase may be unstable as is reflected by the existence of imaginary values in the phonon spectra. The results of the DFT calculations are employed to estimate the entropy and free energies of the alpha and omega phases. It is found that converged phonon calculations lead to an entropy difference which is much smaller than previous estimates, and a much steeper alpha-omega phase transition line.
Let $d\ge1$ and $0<\alpha<2$. Consider the integro-differential operator \[ \mathcal{L}f(x) =\int_{\mathbb{R}^{d}\backslash\{0\}}\left[f(x+h)-f(x)-\chi_{\alpha}(h)\nabla f(x)\cdot h\right]\frac{n(x,h)}{|h|^{d+\alpha}}\mathrm{d}h+\mathbf{1}_{\alpha>1}b(x)\cdot\nabla f(x), \] where $\chi_{\alpha}(h):=\mathbf{1}_{\alpha>1}+\mathbf{1}_{\alpha=1}\mathbf{1}_{\{|h|\le1\}}$, $b:\mathbb{R}^{d}\to\mathbb{R}^{d}$ is bounded measurable, and $n:\mathbb{R}^{d}\times\mathbb{R}^{d}\to\mathbb{R}$ is measurable and bounded above and below respectively by two positive constants. Further, we assume that $n(x,h)$ is H\"older continuous in $x$, uniformly with respect to $h\in\mathbb{R}^{d}$. In the case $\alpha=1,$ we assume additionally $\int_{\partial B_{r}}n(x,h)h\mathrm{d}S_{r}(h)=0$, $\forall r \in (0,\infty)$, where $\mathrm{d}S_{r}$ is the surface measure on $\partial B_{r}$, the boundary of the ball with radius $r$ and center $0$. In this paper, we establish two-sided estimates for the heat kernel of the Markov process associated with the operator $\mathcal{L}$. This extends a recent result of Z.-Q. Chen and X. Zhang.
We prove that on an atomless probability space, the worst-case mean squared error of the Monte-Carlo estimator is minimal if the random points are chosen independently.
The adiabatic self-consistent collective coordinate (ASCC) method is applied to the pairing-plus-quadrupole (P + Q) model Hamiltonian including the quadrupole pairing, and the oblate-prolate shape coexistence phenomena in proton-rich nuclei, 68Se and 72Kr, are investigated. It is shown that the collective path connecting the oblate and prolate local minima runs along a triaxial valley in the beta-gamma plane. Quantum collective Hamiltonian is constructed and low-lying energy spectra and E2 transition probabilities are calculated for the first time using the ASCC method. Basic properties of the shape coexistence/mixing are well reproduced. We also clarify the effects of the time-odd pair field on the collective mass (inertial function) for the large-amplitude vibration and on the rotational moments of inertia about three principal axes.
We determine in closed form the general static solution with cylindrical symmetry to the Brans-Dicke equations for an energy-momentum tensor corresponding to the one of the straight U(1) global string outside the core radius assuming that the Goldstone boson field takes its asymptotic value
Mixture models are well-established learning approaches that, in computer vision, have mostly been applied to inverse or ill-defined problems. However, they are general-purpose divide-and-conquer techniques, splitting the input space into relatively homogeneous subsets in a data-driven manner. Not only ill-defined but also well-defined complex problems should benefit from them. To this end, we devise a framework for spatial regression using mixture density networks. We realize the framework for object detection and human pose estimation. For both tasks, a mixture model yields higher accuracy and divides the input space into interpretable modes. For object detection, mixture components focus on object scale, with the distribution of components closely following that of ground truth the object scale. This practically alleviates the need for multi-scale testing, providing a superior speed-accuracy trade-off. For human pose estimation, a mixture model divides the data based on viewpoint and uncertainty -- namely, front and back views, with back view imposing higher uncertainty. We conduct experiments on the MS COCO dataset and do not face any mode collapse.
Magnetic fields are ubiquitously observed in the interstellar medium (ISM) of present-day star-forming galaxies with dynamically relevant energy densities. Using three-dimensional magneto-hydrodynamic (MHD) simulations of the supernova (SN) driven ISM in the flux-freezing approximation (ideal MHD) we investigate the impact of the magnetic field on the chemical and dynamical evolution of the gas, fragmentation and the formation of molecular clouds. We follow the chemistry with a network of six species (H$^{+}$, H, H$_2$, C$^+$, CO, free electrons) including local shielding effects. We find that magnetic fields thicken the disc by a factor of a few to a scale height of $\sim100\,\mathrm{pc}$, delay the formation of dense (and molecular) gas by $\sim25\,\mathrm{Myr}$ and result in differently shaped gas structures. The magnetised gas fragments into fewer clumps, which are initially at subcritical mass-to-flux ratios, $M/\Phi\approx0.3(M/\Phi)_\mathrm{crit}$, and accrete gas preferentially parallel to the magnetic field lines until supercritial mass-to-flux ratios of up to order 10 are reached. The accretion rates onto molecular clouds scale with $\dot{M}\propto M^{1.5}$. The median of the inter-cloud velocity dispersion is $\sim2-5\,\mathrm{km\,s}^{-1}$ and lower than the internal velocity dispersion in the clouds ($\sim3-7\,\mathrm{km\,s}^{-1}$). However, individual cloud-cloud collisions occur at speeds of a few $10\,\mathrm{km\,s}^{-1}$.
A new method of determining Primary Cosmic Ray mass composition is proposed. The method is based on quasi-localization of the integral equation for the Extensive Air Showers spectrum versus the total number of high energy muons ($E_\mu \geqslant 235$ GeV) and an expansion of the experimentally measured spectrum in spectra of five group of primary nuclei. The cosmic ray mass composition is established in the energy region $10^{14}-10^{16}$ eV. In the region $10^{15}-10^{16}$ eV our analysis points to a lightening of the mass composition from $p+\alpha \simeq 0.54,\ \langle \ln A \rangle \simeq 1.97$ to $p+\alpha \simeq 0.69,\ \langle \ln A \rangle\simeq 1.56$.
Let $R(n) = \sum_{a+b=n} \Lambda(a)\Lambda(b)$, where $\Lambda(\cdot)$ is the von Mangoldt function. The function $R(n)$ is often studied in connection with Goldbach's conjecture. On the Riemann hypothesis (RH) it is known that $\sum_{n\leq x} R(n) = x^2/2 - 4x^{3/2} G(x) + O(x^{1+\epsilon})$, where $G(x)=\Re \sum_{\gamma>0} \frac{x^{i\gamma}}{(\frac{1}{2} + i\gamma)(\frac{3}{2} + i\gamma)}$ and the sum is over the ordinates of the nontrivial zeros of the Riemann zeta function in the upper half-plane. We prove (on RH) that each of the inequalities $G(x) < -0.02093$ and $G(x)> 0.02092$ hold infinitely often, and establish improved bounds under an assumption of linearly independence for zeros of the zeta function. We also show that the bounds we obtain are very close to optimal.
Understanding the influence that copper substrate surface symmetry and oxygen impurities have on the growth of graphene by chemical vapor deposition is important for developing techniques for producing high quality graphene. Therefore, we have studied the growth of graphene by catalytic decomposition of ethylene in an ultra-high vacuum chamber on both a clean Cu(100) surface and a Cu(100) surface pre-dosed with a layer of chemisorbed oxygen. The crystal structure of the graphene films was characterized with \emph{in-situ} low energy electron diffraction. By heating the clean Cu(100) substrate from room temperature to the growth temperature in ethylene, epitaxial graphene films were formed. The crystal quality was found to depend strongly on the growth temperature. At 900 $^\circ$C, well-ordered two-domain graphene films were formed. Pre-dosing the Cu(100) surface with a chemisorbed layer of oxygen before graphene growth was found to adversely affect the crystal quality of the graphene overlayer by inducing a much higher degree of rotational disorder of the graphene grains with respect to the Cu(100) substrate. The growth morphology of the graphene islands during the initial stages of nucleation was monitored with \emph{ex-situ} scanning electron microscopy. The nucleation rate of the graphene islands was observed to drop by an order of magnitude by pre-dosing the Cu(100) surface with a chemisorbed oxygen layer before growth. This reduction in nucleation rate results in the formation of much larger graphene islands. Therefore, the presence of oxygen during graphene growth affects both the relative orientation and average size of grains within the films grown on Cu(100) substrates.
In a number of physical situations, from polarons to Dirac liquids and to non-Fermi liquids, one encounters the "beyond quasiparticles" regime, in which the inelastic scattering rate exceeds the thermal energy of quasiparticles. Transport in this regime cannot be described by the kinetic equation. We employ the Diagrammatic Monte Carlo method to study the mobility of a Fr\"{o}hlich polaron in this regime and discover a number of non-perturbative effects: a strong violation of the Mott-Ioffe-Regel criterion at intermediate and strong couplings, a mobility minimum at $T \sim \Omega$ in the strong-coupling limit ($\Omega$ is the optical mode frequency), a substantial delay in the onset of an exponential dependence of the mobility for $T<\Omega$ at intermediate coupling, and complete smearing of the Drude peak at strong coupling. These effects should be taken into account when interpreting mobility data in materials with strong electron-phonon coupling.
I report the discovery of a new bright variable star in the constellation Scorpius. It is most likely star OGLE BUL-SC23 396060 with position (J2000.0): RA 17:57:59.75, DEC -31:38:07.4. Magnitude range is 14.4 (B) - 21.7 (V). It is visible in the possible outburst on two digitized Palomar Sky Survey photographic plates, which were made 60 years ago. This object was registered as a variable star in the AAVSO VSX under the name of Romanov V1 and with UG: variability type.
We employ ab initio molecular dynamics to simulate the response of hydrogenated amorphous silicon to light exposure (Staebler-Wronski effect). We obtain improved microscopic understanding of PV operation, compute the motion of H atoms, and modes of light-induced degradation of photovoltaics. We clarify existing models of light-induced change in aSi:H and show that the Hydrogen collision model of Branz3 is correct in essentials.
Nearly all modern solid-state quantum processors approach quantum computation with a set of discrete qubit operations (gates) that can achieve universal quantum control with only a handful of primitive gates. In principle, this approach is highly flexible, allowing full control over the qubits' Hilbert space without necessitating the development of specific control protocols for each application. However, current error rates on quantum hardware place harsh limits on the number of primitive gates that can be concatenated together (with compounding error rates) and remain viable. Here, we report our efforts at implementing a software-defined $0\leftrightarrow2$ SWAP gate that does not rely on a primitive gate set and achieves an average gate fidelity of $99.4\%$. Our work represents an alternative, fully generalizable route towards achieving nontrivial quantum control through the use of optimal control techniques. We describe our procedure for computing optimal control solutions, calibrating the quantum and classical hardware chain, and characterizing the fidelity of the optimal control gate.
We show that, for general convolution approximations to a large class of log-correlated fields, including the 2d Gaussian free field, the critical chaos measures with derivative normalisation converge to a limiting measure {\mu}'. This limiting measure does not depend on the choice of approximation. Moreover, it is equal to the measure obtained using the Seneta--Heyde renormalisation at criticality, or using a white-noise approximation to the field.
By an easy trick taken from caloric polynomial theory we construct a family $\mathscr{B}$ of $almost\ regular$ domains for the caloric Dirichlet problem. $\mathscr{B}$ is a basis of the Euclidean topology. This allows to build, with a basically elementary procedure, the Perron solution to the caloric Dirichlet problem on every bounded domain.
We study a zero-range process with two species of interacting particles. We show that the steady state assumes a simple factorised form, provided the dynamics satisfy certain conditions, which we derive. The steady state exhibits a new mechanism of condensation transition wherein one species induces the condensation of the other. We study this mechanism for a specific choice of dynamics.
The electron self-energy of the t1u states in A3C60 (A=K, Rb) is calculated using the so-called GW approximation. The calculation is performed within a model which considers the t1u charge carrier plasmon at 0.5 eV and takes into account scattering of the electrons within the t1u band. A moderate reduction (35 %) of the t1u band width is obtained.
We present new Chandra ACIS-S3 observations of Cassiopeia A which, when combined with earlier ACIS-S3 observations, show evidence for a steady ~ 1.5-2%/yr decline in the 4.2-6.0 keV X-ray emission between the years 2000 and 2010. The computed flux from exposure corrected images over the entire remnant showed a 17% decline over the entire remnant and a slightly larger (21%) decline from regions along the remnant's western limb. Spectral fits of the 4.2-6.0 keV emission across the entire remnant, forward shock filaments, and interior filaments indicate the remnant's nonthermal spectral powerlaw index has steepened by about 10%, with interior filaments having steeper powerlaw indices. Since TeV electrons, which give rise to the observed X-ray synchrotron emission, are associated with the exponential cutoff portion of the electron distribution function, we have related our results to a change in the cutoff energy and conclude that the observed decline and steepening of the nonthermal X-ray emission is consistent with a deceleration of the remnant's ~5000 km/s forward shock of ~10--40 km/s/yr