ShantanuT01/DACTYL-Pretraining huggingface dataset:
We present the results of Quantum Monte Carlo calculations for a two dimensional frustrated Hubbard model coupled to bond phonons. The model is known to have a d-wave superconducting ground state in the limit of large phonon frequency for sufficiently strong electron-phonon coupling. In the absence of electron-phonon coupling the Hubbard interaction U enhances superconducting pairing in the quarter-filled (density $\rho$ = 0.5) band. We show here that at $\rho$ = 0.5 electron-electron and electron-phonon interactions cooperatively reinforce d-wave pairing, while competing with each other at all other densities. Cooperative degrees of freedom are found in many phase transitions and are essential to understanding superconductivity in strongly correlated materials.
Dark energy as a quintessence component causes a typical modification of the background cosmic expansion, which in addition to its clustering properties, can leave a potentially distinctive signature on large scale structures. Many previous studies have investigated this topic, particularly in relation to the non-linear regime of structure formation. However, no careful pre-selection of viable quintessence models with high precision cosmological data was performed. Here we show that this has led to a misinterpretation (and underestimation) of the imprint of quintessence on the distribution of large scale structures. To this purpose we perform a likelihood analysis of the combined Supernova Ia UNION dataset and WMAP5-years data to identify realistic quintessence models. Differences from the vanilla LambdaCDM are especially manifest in the predicted amplitude and shape of the linear matter power spectrum, though these remain within the uncertainties of the SDSS data. We use these models as benchmark for studying the clustering properties of dark matter halos by performing a series of high resolution N-body simulations. We find that realistic quintessence models allow for relevant differences of the dark matter distribution with the respect to the LambdaCDM scenario well into the non-linear regime, with deviations up to 40% in the non-linear power spectrum. Such differences are shown to depend on the nature of DE, as well as the scale and epoch considered. At small scales (k~1-5 h Mpc^{-1}, depending on the redshift) the structure formation process is about 20% more efficient than in LambdaCDM. We show that these imprints are a specific record of the cosmic structure formation history in DE cosmologies and therefore cannot be accounted in standard fitting functions of the non-linear matter power spectrum.
We parameterize Hubbard and spin models for EtMe$_3$Sb[Pd(dmit)$_2$]$_2$ from broken symmetry density functional calculations. This gives a scalene triangular model where the largest net exchange interaction is three times larger than the mean interchain coupling. The chain random phase approximation shows that the difference in the interchain couplings is equivalent to a bipartite interchain coupling, favoring long-range magnetic order. This competes with ring exchange, which favors quantum disorder. Ring exchange wins. We predict that the thermal conductivity, $\kappa$, along the chain direction is much larger than that along the crystallographic axes and that $\kappa/T\rightarrow0$ as $T\rightarrow0$ along the crystallographic axes, but that $\kappa/T\rightarrow\textrm{a constant}>0$ as $T\rightarrow0$ along the chain direction.
Two-dimensional (2D) materials are promising candidates for next-generation electronic devices. In this regime, insulating 2D ferromagnets, which remain rare, are of special importance due to their potential for enabling new device architectures. Here we report the discovery of ferromagnetism in a layered van der Waals semiconductor, VI3, which is based on honeycomb vanadium layers separated by an iodine-iodine van der Waals gap. It has a BiI3-type structure (R-3, No.148) at room temperature, and our experimental evidence suggests that it may undergo a subtle structural phase transition at 78 K. VI3 becomes ferromagnetic at 49 K, below which magneto-optical Kerr effect imaging clearly shows ferromagnetic domains, which can be manipulated by the applied external magnetic field. The optical band gap determined by reflectance measurements is 0.6 eV, and the material is highly resistive.
We perform a pixel-by-pixel analysis of 467 galaxies in the GOODS-VIMOS survey to study systematic effects in extracting properties of stellar populations (age, dust, metallicity and SFR) from pixel colors using the pixel-z method. The systematics studied include the effect of the input stellar population synthesis model, passband limitations and differences between individual SED fits to pixels and global SED-fitting to a galaxy's colors. We find that with optical-only colors, the systematic errors due to differences among the models are well constrained. The largest impact on the age and SFR e-folding time estimates in the pixels arises from differences between the Maraston models and the Bruzual&Charlot models, when optical colors are used. This results in systematic differences larger than the 2{\sigma} uncertainties in over 10 percent of all pixels in the galaxy sample. The effect of restricting the available passbands is more severe. In 26 percent of pixels in the full sample, passband limitations result in systematic biases in the age estimates which are larger than the 2{\sigma} uncertainties. Systematic effects from model differences are reexamined using Near-IR colors for a subsample of 46 galaxies in the GOODS-NICMOS survey. For z > 1, the observed optical/NIR colors span the rest frame UV-optical SED, and the use of different models does not significantly bias the estimates of the stellar population parameters compared to using optical-only colors. We then illustrate how pixel-z can be applied robustly to make detailed studies of substructure in high redshift galaxies such as (a) radial gradients of age, SFR, sSFR and dust and (b) the distribution of these properties within subcomponents such as spiral arms and clumps. Finally, we show preliminary results from the CANDELS survey illustrating how the new HST/WFC3 data can be exploited to probe substructure in z~1-3 galaxies.
The "positive square" of any tensor is presented in a universal and unified manner, valid in Lorentzian manifolds of arbitrary dimension, and independently of any (anti)-symmetry properties of the tensor. For rank-m tensors, the positive square has rank 2m. Positive here means future, that is to say, satisfying the dominant property. The standard energy-momentum and super-energy tensors are recovered as appropriate parts of the general square. A richer structure of principal null directions arises.
In this work, we develop a method to design control pulses for fixed-frequency superconducting qubits coupled via tunable couplers based on local control theory, an approach commonly employed to steer chemical reactions. Local control theory provides an algorithm for the monotonic population transfer from a selected initial state to a desired final state of a quantum system through the on-the-fly shaping of an external pulse. The method, which only requires a unique forward time-propagation of the system wavefunction, can serve as starting point for additional refinements that lead to new pulses with improved properties. Among others, we propose an algorithm for the design of pulses that can transfer population in a reversible manner between given initial and final states of coupled fixed-frequency superconducting qubits.
We study repeated (noncontinuous) measurements on the electron spin in a quantum dot and find that the measurement technique may lead to a different met$ or mechanism to realize nuclear spin polarization. While it may be used in any case, the method is aimed at the further polarization, providing that nuclear spins have been polarized by the existent electrical or optical methods. The feasibility of the method is analyzed. The existing techniques in electron spin measurements are applicable to this scheme. The repeated measurements \emph{deform} the structures of the nuclear wave function and can also serve as $\emph{gates}$ to manipulate nuclear spins.
Fine-grained visual categorization (FGVC) is an important but challenging task due to high intra-class variances and low inter-class variances caused by deformation, occlusion, illumination, etc. An attention convolutional binary neural tree architecture is presented to address those problems for weakly supervised FGVC. Specifically, we incorporate convolutional operations along edges of the tree structure, and use the routing functions in each node to determine the root-to-leaf computational paths within the tree. The final decision is computed as the summation of the predictions from leaf nodes. The deep convolutional operations learn to capture the representations of objects, and the tree structure characterizes the coarse-to-fine hierarchical feature learning process. In addition, we use the attention transformer module to enforce the network to capture discriminative features. The negative log-likelihood loss is used to train the entire network in an end-to-end fashion by SGD with back-propagation. Several experiments on the CUB-200-2011, Stanford Cars and Aircraft datasets demonstrate that the proposed method performs favorably against the state-of-the-arts.
Using the Herschel Space Observatory's Heterodyne Instrument for the Far-Infrared (HIFI), we have performed mapping observations of the 620.701 GHz 5(32)-4(41) transition of ortho-H2O within a roughly 1.5 x 1.5 arcmin region encompassing the Kleinmann-Low nebula in Orion, and pointed observations of that transition toward the Orion South condensation and the W49N region of high-mass star formation. Using the Effelsberg 100 m radio telescope, we obtained ancillary observations of the 22.23508 GHz 6(16)-5(23) water maser transition; in the case of Orion-KL, the 621 GHz and 22 GHz observations were carried out within 10 days of each other. The 621 GHz water line emission shows clear evidence for strong maser amplication in all three sources, exhibiting narrow (roughly 1 km/s FWHM) emission features that are coincident (kinematically and/or spatially) with observed 22 GHz features. Moreover, in the case of W49N - for which observations were available at three epochs spanning a two year period - the spectra exhibited variability. The observed 621 GHz/22 GHz line ratios are consistent with a maser pumping model in which the population inversions arise from the combined effects of collisional excitation and spontaneous radiative decay, and the inferred physical conditions can plausibly arise in gas heated by either dissociative or non-dissociative shocks. The collisional excitation model also predicts that the 22 GHz population inversion will be quenched at higher densities than that of the 621 GHz transition, providing a natural explanation for the observational fact that 22 GHz maser emission appears to be a necessary but insufficient condition for 621 GHz maser emission.
Compactons are solutions of the equations of motion that behave trivially outside a compact region. In general, the operators describing quantum fluctuations above compactons have singularities. However, we show that despite these singularities the quantum theory is well defined. As an example, we calculate the one-loop mass shift of a compacton in a model described by a single real scalar field.
We found a possible ~ 1 hour quasi-periodic oscillation (QPO) in a ~ 55 ks X-ray observation of the narrow-line Seyfert 1 galaxy MCG--06--30--15 made with the XMM-Newton EPIC/pn detector in the energy range 0.3 -- 10 keV. We identify a total modulation of ~ 16% in the light curve and find a $\simeq$ 3670~s quasi-period using Lomb-Scargle periodogram (LSP) and weighted wavelet Z-transform (WWZ) techniques. Our analyses of eight light curves of MCG--06--30--15, indicated the possible presence of an oscillation during one of them. The LSP indicates a statistically significant ($\simeq$ 3$\sigma$) QPO detection. A WWZ analysis shows that the signal at this possible roughly 3670s period is present, and rather persistent, throughout the observation; however, a signal around 8735s is more persistent. We briefly discuss models that can produce X-ray QPOs with such periods in narrow line Seyfert 1 galaxies, as both other claimed QPO detections in this class of AGN had very similar periods.
We study the stability of a compressible magnetic plane Couette flow and show that compressibility profoundly alters the stability properties if the magnetic field has a component perpendicular to the direction of flow. The necessary condition of a newly found instability can be satisfied in a wide variety of flows in laboratory and astrophysical conditions. The instability can operate even in a very strong magnetic field which entirely suppresses other MHD instabilities. The growth time of this instability can be rather short and reach $\sim 10$ shear timescales.
We measure X-ray emission from the outskirts of the cluster of galaxies PKS 0745-191 with Suzaku, determining radial profiles of density, temperature, entropy, gas fraction, and mass. These measurements extend beyond the virial radius for the first time, providing new information about cluster assembly and the diffuse intracluster medium out to ~1.5 r_200, (r_200 ~ 1.7 Mpc ~ 15'). The temperature is found to decrease by roughly 70 per cent from 0.3-1 r_200. We also see a flattening of the entropy profile near the virial radius and consider the implications this has for the assumption of hydrostatic equilibrium when deriving mass estimates. We place these observations in the context of simulations and analytical models to develop a better understanding of non-gravitational physics in the outskirts of the cluster.
Consider the energy-critical focusing wave equation in space dimension $N\geq 3$. The equation has a nonzero radial stationary solution $W$, which is unique up to scaling and sign change. It is conjectured (soliton resolution) that any radial, bounded in the energy norm solution of the equation behaves asymptotically as a sum of modulated $W$s, decoupled by the scaling, and a radiation term. A nonradiative solution of the equation is by definition a solution whose energy in the exterior $\{|x|>|t|\}$ of the wave cone vanishes asymptotically as $t\to +\infty$ and $t\to -\infty$. In a previous work (Cambridge Journal of Mathematics 2013, arXiv:1204.0031), we have proved that the only radial nonradiative solutions of the equation in three space dimensions are, up to scaling, $0$ and $\pm W$. This was crucial in the proof of soliton resolution in 3 space dimension.   In this paper, we prove that the initial data of a radial nonradiative solution in odd space dimension have a prescribed asymptotic behaviour as $r\to \infty$. We will use this property for the proof of soliton resolution, for radial data, in all odd space dimensions. The proof uses the characterization of nonradiative solutions of the linear wave equation in odd space dimensions obtained by Lawrie, Liu, Schlag and the second author (Advances in Mathematics, 2015, arXiv:1409.3643) .   We also study the propagation of the support of nonzero radial solutions with compactly supported initial data, and prove that these solutions cannot be nonradiative.
We present a joint experimental and theoretical study of parametric resonance of spin wave eigenmodes in Ni$_{80}$Fe$_{20}$/Pt bilayer nanowires. Using electrically detected magnetic resonance, we measure the spectrum of spin wave eigenmodes in transversely magnetized nanowires and study parametric excitation of these eigenmodes by a microwave magnetic field. We also develop an analytical theory of spin wave eigenmodes and their parametric excitation in the nanowire geometry that takes into account magnetic dilution at the nanowire edges. We measure tuning of the parametric resonance threshold by antidamping spin Hall torque from a direct current for the edge and bulk eigenmodes, which allows us to independently evaluate frequency, damping and ellipticity of the modes. We find good agreement between theory and experiment for parametric resonance of the bulk eigenmodes but significant discrepancies arise for the edge modes. The data reveals that ellipticity of the edge modes is significantly lower than expected, which can be attributed to strong modification of magnetism at the nanowire edges. Our work demonstrates that parametric resonance of spin wave eigenmodes is a sensitive probe of magnetic properties at edges of thin-film nanomagnets.
We analyzed the combined 142 years sunspot-group data from Greenwich Photoheliograpic Results (GPR) and Debrecen Photoheliographic Data (DPD) and determined the yearly mean residual rotation rate and the meridional velocity of sunspot groups in different 5-degree latitude intervals. The residual rotation rate is found to be -120 m/s to 80 m/s. In a large number of solar cycles the rotation is to some extent weaker during maxima than that of during minima. There exist alternate bands of equatorward and poleward merdional motions. The equatorward motion is dominant mostly around the maxima of solar cycles with velocity 8-12 m/s, whereas the poleward motion is dominant mostly around the minima but with a relatively weak velocity, only 4-6 m/s. This analysis suggests the existence of equatorward migrating alternate bands of slower and faster than average rotation within the activity belt and no clear equatorward or poleward migrating bands of meridional motions. A statistically significant anticorrelation exists between the meridional motion and residual rotation. The corresponding linear-least-squares best-fit is found to be reasonably good (slope, -0.028 + or - 0.008, is about 3.5 times larger than its standard deviation). The significant negative value of the slope indicates the existence of a strong angular momentum transport toward equator. The slope leads sunspot number (SN) by about 4 and 9 years. The Morlet wavelet spectrum of the slope suggests the existence of approximate 11-year periodicity in the slope almost throughout the data window, but it was very weak during 1920-1940.Overall the results suggest there exits a strong relationship between the slope and amount of activity during a solar cycle. However, no relationship is found between the slope and strength of activity on a long-time scale (longer than 11-year period).
We apply the prescription proposed in hep-th/0307197 for non-abelian expansion of S-matrix elements, to the S-matrix element of four tachyons and one gauge field in superstring theory. We show that the leading order terms of the expansion are in perfect agreement with the non-abelian generalization of the tachyon DBI action in which the tachyon potential is $V(T)=1+\pi\alpha' m^2T^2+\frac{1}{2!}(\pi\alpha' m^2T^2)^2+...$ where $m^2=-1/(2\alpha')$ is the mass of tachyon. This calculation fixes the coefficient of $T^4$ in the potential without on-shell ambiguity.
We compute the decay rate for the process $\eta_c\to p\bar p$ using an effective helicity-flipping proton-antiproton-gluon vertex which incorporates nonperturbative chiral symmetry breaking effects induced by instantons. We fix the strength of the vertex by requiring it to account for the screening of the proton's axial charge observed in deep-inelastic scattering, and we estimate the size of the instanton effects by assuming them to depend linearly on the instanton density. We find that, despite a large suppression, the instanton-induced process occurs with a sizable rate comparable to the observed one, whereas the process is forbidden in perturbative QCD and not understood using standard methods.
In this paper we will investigate the singular points of the following unstable free boundary problem: {equation}\label{Eq} \Delta u= -\chi_{\{u>0\}} \quad\quad\textrm{in} B_1(0) {equation} where $\chi_{\{u>0\}}$ is the characteristic function of the set $\{u>0\}$.
We propose a scheme that is able to generate the microwave controlled optical double optome-chanical induced transparency (OMIT) in a hybrid piezo-optomechanical cavity system, which a piezoelectric optomechanical crystal AlN-nanobeam resonator is placed in a superconducting microwave cavity, and the AlN-nanobeam resonator can be simultaneously driven by both the optical field via the radiation pressure and the microwave field via the piezoelectric interaction. We show that in the presence of a strong pumped optical field applied to the optomechanical crystal cavity through the optical waveguide and an intensely stimulated microwave field applied to the superconducting microwave cavity, a double-OMIT window can be observed in the weak output probe field. The mechanism is that a N-type four-level system can be formed by the system, when two driving fields and a probe field are applied to the corresponding levels, under the effect of quantum interference between different energy level pathways, the third-order nonlinear absorption is enhanced by the constructive quantum interference while the linear absorption is inhibited by the destruc- tive quantum interference, as a result, the double-OMIT window is generated. Our scheme can be applied to realize high-speed optical switches, high-resolution spectroscopy, coherent population trapping or quantum information processing in the solid state quantum systems.
Over the last decade, implementations of several desingularization algorithms have appeared in various contexts. These differ as widely in their methods and in their practical efficiency as they differ in the situations in which they may be applied. The purpose of this article is to give a brief overview over a selection of these approaches and the applicability of the respective implementations in Singular.
Recent experimental data on space-like and time-like form factors of the nucleon are analyzed in terms of a two-component model with a quark-like intrinsic three-quark structure and quark-antiquark pairs.
We provide the first example of a communication model and a distributed task, for which there exists a realistic quantum protocol which is asymptotically more efficient than any classical protocol, both in the communication and the information resources. For this, we extend a recently proposed coherent state mapping for quantum communication protocols, introduce the notion of multiplexed coherent state fingerprints and show how to use them to design an efficient quantum protocol for estimating the Euclidean distance of two real vectors within a constant factor.
The sigma clique cover number (resp. sigma clique partition number) of graph G, denoted by scc(G) (resp. scp(G)), is defined as the smallest integer k for which there exists a collection of cliques of G, covering (resp. partitioning) all edges of G such that the sum of sizes of the cliques is at most k. In this paper, among some results we provide some tight bounds for scc and scp.
We compute various kinematical distributions for one-jet and two-jet inclusive photoproduction at HERA. Our results are accurate to next-to-leading order in QCD. We use the subtraction method for the cancellation of infrared singularities. We perform a thorough study of the reliability of QCD predictions; in particular, we consider the scale dependence of our results and discuss the cases when the perturbative expansion might break down. We also deal with the problem of the experimental definition of the pointlike and hadronic components of the incident photon, and briefly discuss the sensitivity of QCD predictions upon the input parameters of the calculation, like $\alpha_S$ and the parton densities.