ShantanuT01/DACTYL-Pretraining huggingface dataset:
Parallel tempering and population annealing are both effective methods for simulating equilibrium systems with rough free energy landscapes. Parallel tempering, also known as replica exchange Monte Carlo, is a Markov chain Monte Carlo method while population annealing is a sequential Monte Carlo method. Both methods overcome the exponential slowing associated with high free energy barriers. The convergence properties and efficiency of the two methods are compared. For large systems, population annealing initially converges to equilibrium more rapidly than parallel tempering for the same amount of computational work. However, parallel tempering converges exponentially and population annealing inversely in the computational work so that ultimately parallel tempering approaches equilibrium more rapidly than population annealing.
We consider the reversible exclusion process with reservoirs on arbitrary networks. We characterize the spectral gap, mixing time, and mixing window of the process, in terms of certain simple statistics of the underlying network. Among other consequences, we establish a non-conservative analogue of Aldous's spectral gap conjecture, and we show that cutoff occurs if and only if the product condition is satisfied. We illustrate this by providing explicit cutoffs on discrete lattices of arbitrary dimensions and boundary conditions, which substantially generalize recent one-dimensional results. We also obtain cutoff phenomena in relative entropy, Hilbert norm, separation distance and supremum norm. Our proof exploits negative dependence in a novel, simple way to reduce the understanding of the whole process to that of single-site marginals. We believe that this approach will find other applications.
Recent advances in numerical algorithms and computational power have enabled first-principles simulations of pulsar magnetospheres using Particle-in-Cell (PIC) techniques. These ab-initio simulations seem to indicate that pair creation through photon-photon collision at the light cylinder is required to sustain the pulsar engine. However, for many rotation-powered pulsars pair creation operates effectively only near the stellar surface where magnetic field is high. How these "weak pulsars" fill their magnetospheres without efficient photon-photon pair conversion in the outer magnetosphere is still an open question. In this paper, we present a range of self-consistent solutions to the pulsar magnetosphere that do not require pair production near the light cylinder. When pair production is very efficient near the star, the pulsar magnetosphere converges to previously-reported solutions. However, in the intermediate regime where pair supply is barely enough to sustain the magnetospheric current, we observe a time-dependent solution with quasi-period about half of the rotation period. This new quasi-periodic solution may explain the observed pulsar death line without invoking multipolar components near the star, and can potentially explain the core vs. conal emission patterns observed in pulsar radio signals.
In1-xMnxAs diluted magnetic semiconductor (DMS) thin films have been grown using metalorganic vapor phase epitaxy (MOVPE). Tricarbonyl(methylcyclopentadienyl)manganese was used as the Mn source. Nominally single-phase, epitaxial films were achieved with Mn content as high as x=0.14 using growth temperatures Tg>475 C. For lower growth temperatures and higher Mn concentrations, nanometer scale MnAs precipitates were detected within the In1-xMnxAs matrix. Magnetic properties of the films were investigated using a superconducting quantum interference device (SQUID) magnetometer. Room-temperature ferromagnetic order was observed in a sample with x=0.1. Magnetization measurements indicated a Curie temperature of 333 K and a room-temperature saturation magnetization of 49 emu/cm^3. The remnant magnetization and the coercive field were small, with values of 10 emu/cm^3 and 400 Oe, respectively. A mechanism for this high-temperature ferromagnetism is discussed in light of the recent theory based on the formation of small clusters of a few magnetic atoms.
The spin Hall conductivity (SHC) and anomalous Hall conductivity (AHC) in more than 120 full Heusler compounds are calculated using density functional theory in a high-throughtput way. The electronic structures are mapped to the Wannier basis and the linear response theory is used to get the conductivity. Our results show that the mechanism under the SHC or AHC cannot be simply related to the valence electron numbers or atomic weights, is related to the very details of the electronic structure, which can only be obtained by calculations. A high throughput calculation is efficient to screen out the desired materials. According to our present results, Cu2CoSn, as well as Co2MnAl and Co2MnGa are candidates in spintronic materials regarding to their high SHC and AHC values, which can benefit the spin-torque-driven nanodevices.
We have created new dust temperature and column density maps of Perseus, Ophiuchus and Serpens using 60 and 100 micron data from the IRIS recalibration of IRAS data. We describe an optimized method for finding the dust temperature, emissivity spectral index, and optical depth using optical and NIR extinction maps. The creation of these temperature and extinction maps (covering tens of square degrees of molecular clouds) is one of the first results from the ongoing COordinated Molecular Probe Line Extinction Thermal Emission (COMPLETE) Survey of Star Forming regions. However, while the extinctions derived from the IRIS emission maps are globally accurate, we warn that FIR emission is not a good proxy for extinction on the scale of one pixel (5').
Consider a discrete time, ergodic Markov chain with finite state space which is started from stationarity. Fill and Lyzinski (2014) showed that, in some cases, the hitting time for a given state may be represented as a sum of a geometric number of IID random variables. We extend this result by giving explicit bounds on the distance between any such hitting time and an appropriately chosen geometric sum, along with other related approximations. The compounding random variable in our approximating geometric sum is a strong stationary time for the underlying Markov chain; we also discuss the approximation and construction of this distribution.
We propose a microscopic simulation for quark many-body system based on molecular dynamics. Using color confinement and one-gluon exchange potentials together with the meson exchange potentials between quarks, we construct nucleons and nuclear/quark matter. Statistical feature and the dynamical change between confinement and deconfinement phases are studied with this molecular dynamics simulation.
We report the discovery of Andromeda X, a new dwarf spheroidal satellite of M31, based on stellar photometry from the Sloan Digital Sky Survey (SDSS). Using follow-up imaging data we have estimated its distance and other physical properties. We find that Andromeda X has a dereddened central surface brightness of mu_V,0 ~ 26.7 mag arcsec^-2 and a total apparent magnitude of V_tot ~ 16.1, which at the derived distance modulus, (m - M)_0 ~ 24.12 - 24.34, yields an absolute magnitude of M_V ~ -8.1 +/- 0.5; these values are quite comparable to those of Andromeda IX, a previously-discovered low luminosity M31 satellite. The discoveries of Andromeda IX and Andromeda X suggest that such extremely faint satellites may be plentiful in the Local Group.
We discuss in this paper the subleading contact interactions, or counterterms, in the 3P0 channel of nucleon-nucleon scattering up to O(Q^3), where, already at leading order, Weinberg's original power counting (WPC) scheme fails to fulfill renormalization group invariance due to the singular attraction of one-pion exchange. Treating the subleading interactions as perturbations and using renormalization group invariance as the criterion, we investigate whether WPC, although missing the leading order, could prescribe correct subleading counterterms. We find that the answer is negative and, instead, that the structure of counterterms agrees with a modified version of naive dimensional analysis. Using 3P0 as an example, we also study the cutoffs where the subleading potential can be iterated together with the leading one.
We consider the zero-temperature random-field Ising model in the presence of an external field, on ladders and in one dimension with finite range interactions, for unbounded continuous distributions of random fields, and show that there is no jump discontinuity in the magnetizations for any quasi-one dimensional model. We show that the evolution of the system at an external field can be described by a stochastic matrix and the magnetization can be obtained using the eigenvector of the matrix corresponding to the eigenvalue one, which is continuous and differentiable function of the external field.
Gaugino condensation plays a crucial role in the formation of dS vacua. However, the theory of this effect is still incomplete. In 4d the perfect square nature of gaugino couplings follows from the square of auxiliaries in the supergravity action. We explain here why the supersymmetric non-Abelian Dp-brane action, which is the basis for the theory of 10d gaugino condensation, must have a 4-gaugino coupling. This term in the Einstein-Yang-Mills 10d supergravity is a part of the perfect square, mixing a 3-form with gaugino bilinear. The perfect square term follows from the superspace geometry, being a square of the superspace torsion. The supercovariant equation of motion for gaugino on the non-Abelian Dp-brane also involves a supertorsion in agreement with the perfect square term in the action.
We examine the growth of the Weyl curvature in two examples of naked singularity formation in spherical gravitational collapse - dust and the Vaidya spacetime. We find that the Weyl scalar diverges along outgoing radial null geodesics as they meet the naked singularity in the past. The implications of this result for the Weyl curvature hypothesis are discussed. We mention the possibility that although classical general relativity admits naked singularity solutions arising from gravitational collapse, the second law of thermodynamics could forbid their occurrence in nature. The method can also be used to compare the relative importance of initial data and that of the energy-momentum tensor in deciding the metric solution in any general case.
Polymomentum canonical theories, which are manifestly covariant multi-parameter generalizations of the Hamiltonian formalism to field theory, are considered as a possible basis of quantization. We arrive at a multi-parameter hypercomplex generalization of quantum mechanics to field theory in which the algebra of complex numbers and a time parameter are replaced by the space-time Clifford algebra and space-time variables treated in a manifestly covariant fashion. The corresponding covariant generalization of the Schroedinger equation is shown to be consistent with several aspects of the correspondence principle such as a relation to the De Donder-Weyl Hamilton-Jacobi theory in the classical limit and the Ehrenfest theorem. A relation of the corresponding wave function (over a finite dimensional configuration space of field and space-time variables) to the Schroedinger wave functional in quantum field theory is examined in the ultra-local approximation.
Transition metal dichalcogenides are rich in their structural phases, e.g. 1T-TaS2 and 1T-TaSe2 form charge density wave (CDW) under low temperature with interesting and exotic properties. Here, we present a systematic study of different structures in two-dimensional TaX2 (X=S, Se, Te) using density functional theory calculations with consideration of van der Waals interaction. All the normal phases present metal characteristics with various ground state and magnetic properties. The lattice reconstruction of CDW drastically affects the electronic and structural characteristics of 1T-TaS2 and 1T-TaSe2, leading to a transition from metal to insulator and an emergence of magnetic moment within periodic atomic clusters called the Star of David. The evaluated Heisenberg couplings indicate the weak ferromagnetic coupling between the clusters in monolayer. Furthermore, in bilayer commensurate CDW cases, we find intriguing phenomenon of the varying magnetic properties with different stacking orders. The magnetic moment in each layer disappears when two layers are coupled, but may sustain in certain stackings of interlayer antiferromagnetic configurations.
A new quantum correlation in terms of the average distance between the reduced state and the $i$-th output reduced states under local von Neumann measurements is proposed. It is shown that only the product states do not contain this quantum correlation and thus it is different from both the quantum discord (QD) [Phys. Rev. Lett. \textbf{88}, 017901 (2001)] and the measurement-induced nonlocality (MIN) [Phys. Rev. Lett. \textbf{106}, 120401(2011)]. For pure states, it is twice of the quantity MIN, and is smaller than QD and entanglement of formation (EOF). A general analytical formula is given and a lower bound for the two qubits case is obtained. Furthermore, we compare it with EOF and QD through the Werner state and the isotropic state respectively.
We present in this article an optical potential for the $\pi$-nucleus interaction that can be used in various studies involving $\pi$-nucleus channels. Based on earlier treatments of the low energy $\pi$-nucleus optical potential, we have derived a potential expression applicable from threshold up to the $\Delta$-resonance region. We extracted the impulse approximation form for this potential from the $\pi-N$ scattering amplitude and then added to it kinematical and physical corrections. The kinematic corrections arise from transforming the impulse approximation expression from the $\pi-N$ center of mass frame to the $\pi$-nucleus center of mass frame, while the physical corrections arise mostly from the many-body nature of the $\pi$-nucleus interaction. By taking advantage of the experimental progress in our knowledge of the $\pi-N$ process, we have updated earlier treatments with parameters calculated from state-of-the-art experimental measurements.
In this article we compare different conditions on abelian schemes with real multiplication which occur in the integral models of the Hilbert-Blumenthal Shimura variety considered by Rapoport, Deligne, Pappas and Kottwitz. We show that the models studied by Deligne/Pappas and Kottwitz are isomorphic over Spec Z_(p). We also examine the associated local models and prove that they are equal.
A class of graphene wound into three-dimensional periodic curved surfaces ("graphitic zeolites") is proposed and their electronic structures are obtained to explore how the massless Dirac fermions behave on periodic surfaces. We find in the tight-binding model that the low-energy band structure around the charge neutrality point is dominated by the topology (cubic or gyroid) of the periodic surface as well as by the spatial period $L$ in modulo 3 in units of the lattice constant. In both of cubic and gyroid cases the Dirac electrons become massive around the charge neutrality point, where the band gap is shown to scale as $1/L$ within each mod-3 class. Wave functions around the gap are found to have amplitudes sharply peaked around the topological defects that are required to deform the graphene sheet into a three-dimensional periodic surface, and this is shown to originate from non-trivial Bloch phases at $K$ and $K'$ points of the original graphene.
The single production of fourth family sneutrino $\tilde{\nu}_{4}$ via R-parity violating interactions in electron-positron collisions has been investigated. We study the decays of $\tilde{\nu}_{4}$ into different flavor dilepton $e^{\pm}\mu^{\mp}$ via R-parity violation. It is shown that R-parity violating couplings $(\lambda_{411},\lambda_{412})$ down to 0.001 will be reachable at future linear colliders which would provide better accuracy comparing to the indirect measurements as complementary to the LHC results.
The fast simultaneous hadronization and chemical freeze out of supercooled quark-gluon plasma, created in relativistic heavy ion collisions, leads to the re-heating of the expanding matter and to the change in a collective flow profile. We use the assumption of statistical nature of the hadronization process, and study quantitatively the freeze out in the framework of hydrodynamical Bjorken model with different quark-gluon plasma equations of state.
We present (sub)millimeter line and continuum observations in a mosaicing mode of the massive star forming region Cepheus A East made with the Submillimeter Array (SMA). Our mosaic covers a total area of about 3$'$ $\times$ 12$'$ centered in the HW 2/3 region. For the first time, this observational study encloses a high angular resolution ($\sim$ 3$''$) together with a large scale mapping of Cepheus A East. We report compact and high velocity $^{12}$CO(2-1) emission associated with the multiple east-west bright H$_2$ condensations present in the region. Blueshifted and redshifted gas emission is found towards the east as well as west of HW 2/3. The observations suggest the presence of multiple large-scale east-west outflows that seems to be powered at smaller scales by radio sources associated with the young stars HW2, HW3c and HW3d. A kinematical study of part of the data suggests that the molecular outflow powered by HW2 is precesing with time as recently reported. Our data reveal five periodic ejections of material separated approximately every 10$^\circ$ as projected in the plane of the sky. The most recent ejections appear to move toward the plane of the sky. An energetic explosive event as the one that occurred in Orion BN/KL or DR21 does not explain the kinematics, and the dynamical times of the multiple ejections found here. The continuum observations only revealed a strong millimeter source associated with the HW 2/3 region. High angular resolution observations allow us to resolve this extended dusty object in only two compact sources (with spatial sizes of approximately 300 AU) associated with HW2 and HW3c. Finally, the bright optical/X-Ray HH 168 -- GDD37 object might be produced by strong shocks related with the outflow from HW3c.
Angle resolved photoemission spectroscopy (ARPES) studies were performed on two compounds (TlBiTe$_2$ and TlBiSe$_2$) from a recently proposed three dimensional topological insulator family in Thallium-based III-V-VI$_2$ ternary chalcogenides. For both materials, we show that the electronic band structures are in broad agreement with the $ab$ $initio$ calculations; by surveying over the entire surface Brillouin zone (BZ), we demonstrate that there is a single Dirac cone reside at the center of BZ, indicating its topological non-triviality. For TlBiSe$_2$, the observed Dirac point resides at the top of the bulk valance band, making it a large gap ($\geq$200$meV$) topological insulator; while for TlBiTe$_2$, we found there exist a negative indirect gap between the bulk conduction band at $M$ point and the bulk valance band near $\Gamma$, making it a semi-metal at proper doping. Interestingly, the unique band structures of TlBiTe$_2$ we observed further suggest TlBiTe$_2$ may be a candidate for topological superconductors.
Video super-resolution (VSR) aims to restore a photo-realistic high-resolution (HR) video frame from both its corresponding low-resolution (LR) frame (reference frame) and multiple neighboring frames (supporting frames). Due to varying motion of cameras or objects, the reference frame and each support frame are not aligned. Therefore, temporal alignment is a challenging yet important problem for VSR. Previous VSR methods usually utilize optical flow between the reference frame and each supporting frame to wrap the supporting frame for temporal alignment. Therefore, the performance of these image-level wrapping-based models will highly depend on the prediction accuracy of optical flow, and inaccurate optical flow will lead to artifacts in the wrapped supporting frames, which also will be propagated into the reconstructed HR video frame. To overcome the limitation, in this paper, we propose a temporal deformable alignment network (TDAN) to adaptively align the reference frame and each supporting frame at the feature level without computing optical flow. The TDAN uses features from both the reference frame and each supporting frame to dynamically predict offsets of sampling convolution kernels. By using the corresponding kernels, TDAN transforms supporting frames to align with the reference frame. To predict the HR video frame, a reconstruction network taking aligned frames and the reference frame is utilized. Experimental results demonstrate the effectiveness of the proposed TDAN-based VSR model.
Inspired by the results of Rhin and Viola (2001), the purpose of this work is to elaborate on a series representation for $\zeta \left( 3\right)$ which only depends on one single integer parameter. This is accomplished by deducing a Hermite-Pad\'e approximation problem using ideas of Sorokin (1998). As a consequence we get a new recurrence relation for the approximation of $\zeta(3)$ as well as a corresponding new continued fraction expansion for $\zeta(3)$, which do no reproduce Ap\'ery's phenomenon, i.e., though the approaches are different, they lead to the same sequence of diophantine approximations to $\zeta \left( 3\right) $. Finally, the convergence rates of several series representations of $\zeta(3)$ are compared.
By analysing the high momentum features of the nucleon momentum distribution in light and complex nuclei, it is argued that the basic two-nucleon configurations generating the structure of the nucleon Spectral Function at high values of the nucleon momentum and removal energy, can be properly described by a factorised ansatz for the nuclear wave function, which leads to a nucleon Spectral Function in the form of a convolution integral involving the momentum distributions describing the relative and center-of-mass motion of a correlated nucleon-nucleon pair embedded in the medium. The Spectral Functions of $^3He$ and infinite nuclear matter resulting from the convolution formula and from many-body calculations are compared, and a very good agreement in a wide range of values of nucleon momentum and removal energy is found. Applications of the model to the analysis of inclusive and exclusive processes are presented, illustrating those features of the cross section which are sensitive to that part of the Spectral Function which is governed by short-range and tensor nucleon-nucleon correlations.
Accretion disk instabilities are briefly reviewed. Some details are given to the short-wavelength thermal instabilities and the convective instabilities. Time-dependent calculations of two-dimensional advection-dominated accretion flows are presented.