ShantanuT01/DACTYL-Pretraining huggingface dataset:
Cosmological parameter estimation from forthcoming experiments promise to reach much greater precision than current constraints. As statistical errors shrink, the required control over systematic errors increases. Therefore, models or approximations that were sufficiently accurate so far, may introduce significant systematic biases in the parameter best-fit values and jeopardize the robustness of cosmological analyses. We present a general expression to estimate a priori the systematic error introduced in parameter inference due to the use of insufficiently good approximations in the computation of the observable of interest or the assumption of an incorrect underlying model. Although this methodology can be applied to measurements of any scientific field, we illustrate its power by studying the effect of modeling the angular galaxy power spectrum incorrectly. We also introduce Multi_CLASS, a new, public modification of the Boltzmann code CLASS, which includes the possibility to compute angular cross-power spectra for two different tracers. We find that significant biases in most of the cosmological parameters are introduced if one assumes the Limber approximation or neglects lensing magnification in modern galaxy survey analyses, and the effect is in general larger for the multi-tracer case, especially for the parameter controlling primordial non-Gaussianity of the local type, $f_{\rm NL}$.
We investigate seed magnetic field generation in the early universe by radiation force of first stars. In the previous study with steady assumption, large amplitudes(10^{-15} G for first stars, 10^{-11}G for QSOs) are predicted. In this study, we formulate this issue in unsteady framework. Then, we consider a specific model of magnetic field generation around a very massive first star. Consequently, 1) we find steady assumption is not valid in realistic situation, and 2) obtain much smaller magnetic field strength than predicted by Langer et al. (2003). In addition, we find momentum transfer process during photoionization is more important than Thomson scattering. The resultant magnetic flux density around the first star is < 10^{-19}G. These seed magnetic field will not affect subsequent star formation in the neighbor of first stars.
In this survey article we describe moduli spaces of simple, stable, and semistable sheaves on K3 surfaces, following the work of Mukai, O'Grady, Huybrechts, Yoshioka, and others. We also describe some recent developments, including applications to the study of Chow rings of K3 surfaces, determination of the ample and nef cones of irreducible holomorphic symplectic manifolds, and moduli spaces of Bridgeland stable complexes of sheaves.
We show an attempt to establish the zeroth law of thermodynamics within the framework of nonextensive statistical mechanics based on the classic normalization $\texttt{Tr}\hat{\rho}=1$ and the unnormalized expectation $x=\texttt{Tr}\hat{\rho}^q\hat{x}$. The first law of thermodynamics and the definition of heat and work in this formalism are discussed.
The body pose of a person wearing a camera is of great interest for applications in augmented reality, healthcare, and robotics, yet much of the person's body is out of view for a typical wearable camera. We propose a learning-based approach to estimate the camera wearer's 3D body pose from egocentric video sequences. Our key insight is to leverage interactions with another person---whose body pose we can directly observe---as a signal inherently linked to the body pose of the first-person subject. We show that since interactions between individuals often induce a well-ordered series of back-and-forth responses, it is possible to learn a temporal model of the interlinked poses even though one party is largely out of view. We demonstrate our idea on a variety of domains with dyadic interaction and show the substantial impact on egocentric body pose estimation, which improves the state of the art. Video results are available at http://vision.cs.utexas.edu/projects/you2me/
Based upon recent evidence from abundance patterns of chemical elements in solar energetic particles (SEPs), and, ironically, the belated inclusion of H and He, we can distinguish four basic SEP populations: (1) SEP1 - pure "impulsive" SEPs are produced by magnetic reconnection in solar jets showing steep power-law enhancements of 1<= Z <= 56 ions versus charge-to-mass ratio A/Q from a ~3 MK plasma. (2) SEP2 - ambient ions, mostly protons, plus SEP1 ions reaccelerated by the shock wave driven by the narrow coronal mass ejection (CME) from the same jet. (3) SEP3 - a "gradual" SEP event is produced when a moderately fast, wide CME-driven shock wave barely accelerates ambient protons while preferentially accelerating accumulated remnant SEP1 ions from an active region fed by multiple jets. (4) SEP4 - a gradual SEP event is produced when a very fast, wide CME-driven shock wave is completely dominated by ambient coronal seed population of 0.8 - 1.8 MK plasma usually producing a full power law vs. A/Q for 1<= Z <= 56 ions. We begin with element abundances in the photosphere that are fractionated during transport up to the corona based upon their first ionization potential (FIP); this important "FIP effect" for SEPs provides our reference abundances and is different for SEPs from that for the solar wind. We then show evidence for each of the processes of acceleration, reacceleration, and transport that conspire to produce the four abundances patterns we distinguish.
In this paper, we use Stein's method to obtain optimal bounds, both in Kolmogorov and in Wasserstein distance, in the normal approximation for the empirical distribution of the ground state of a many-interacting-worlds harmonic oscillator proposed by Hall, Deckert, and Wiseman [Phys. Rev. X. (2014)]. Our bounds on the Wasserstein distance solve a conjecture of McKeague and Levin [Ann. Appl. Probab. (2016)].
Controlling the magnetization reversal process of magnetic elements is important for a wide range of applications that make use of magnetoresistive effects, but is difficult to achieve for devices that require adjacent thin film structures capable of contacting an individual molecule or quantum dot. We report on the fabrication and measurement of ferromagnetic break junction devices with planar, elliptical leads to address the particular challenge of controlling the relative magnetization alignment between neighboring electrodes. Low temperature transport measurements, supported by finite-element micromagnetic simulations, are used to characterize the magnetoresistance response across a range of conductance levels. We demonstrate that an in-plane external field applied parallel to the hard axis of the ellipses may be used to controllably switch the magnetization of the source and drain electrodes between monodomain-like parallel and antiparallel configurations for devices in the tunneling regime.
Solar oscillations are expected to be excited by turbulent flows in the intergranular lanes near the solar surface. Time series recorded by the IMaX instrument aboard the {\sc Sunrise} observatory reveal solar oscillations at high resolution, which allow studying the properties of oscillations with short wavelengths. We analyze two times series with synchronous recordings of Doppler velocity and continuum intensity images with durations of 32\thinspace min and 23\thinspace min, resp., recorded close to the disk center of the Sun to study the propagation and excitation of solar acoustic oscillations. In the Doppler velocity data, both the standing acoustic waves and the short-lived, high-degree running waves are visible. The standing waves are visible as temporary enhancements of the amplitudes of the large-scale velocity field due to the stochastic superposition of the acoustic waves. We focus on the high-degree small-scale waves by suitable filtering in the Fourier domain. Investigating the propagation and excitation of $f$- and $p_1$-modes with wave numbers $k > 1.4$\thinspace 1/Mm we find that also exploding granules contribute to the excitation of solar $p$-modes in addition to the contribution of intergranular lanes.
Deep neural networks have been the driving force behind the success in classification tasks, e.g., object and audio recognition. Impressive results and generalization have been achieved by a variety of recently proposed architectures, the majority of which are seemingly disconnected. In this work, we cast the study of deep classifiers under a unifying framework. In particular, we express state-of-the-art architectures (e.g., residual and non-local networks) in the form of different degree polynomials of the input. Our framework provides insights on the inductive biases of each model and enables natural extensions building upon their polynomial nature. The efficacy of the proposed models is evaluated on standard image and audio classification benchmarks. The expressivity of the proposed models is highlighted both in terms of increased model performance as well as model compression. Lastly, the extensions allowed by this taxonomy showcase benefits in the presence of limited data and long-tailed data distributions. We expect this taxonomy to provide links between existing domain-specific architectures. The source code is available at \url{https://github.com/grigorisg9gr/polynomials-for-augmenting-NNs}.
The present note considers a certain family of sums indexed by the set of fixed length compositions of a given number. The sums in question cannot be realized as weighted compositions. However they can be be related to the hypergeometric function, thereby allowing one to factorize the corresponding generating polynomials. This factorization leads to some interesting identities.
It was recently discovered that the quantum correlations of a pair of disentangled qubits, as measured by the quantum discord, can increase solely because of their interaction with a local dissipative bath. Here, we show that a similar phenomenon can occur in continuous-variable bipartite systems. To this aim, we consider a class of two-mode squeezed thermal states and study the behavior of Gaussian quantum discord under various local Markovian non-unitary channels. While these in general cause a monotonic drop of quantum correlations, an initial rise can take place with a thermal-noise channel.
In this paper, we build from previous work (Bustard et al. 2018) and present simulations of recent (within the past Gyr), magnetized, cosmic ray driven outflows from the Large Magellanic Cloud (LMC), including our first attempts to explicitly use the derived star formation history of the LMC to seed outflow generation. We run a parameter set of simulations for different LMC gas masses and cosmic ray transport treatments, and we make preliminary comparisons to published outflow flux estimates, neutral and ionized hydrogen observations, and Faraday rotation measure maps. We additionally report on the gas mass that becomes unbound from the LMC disk and swept by ram pressure into the Trailing Magellanic Stream. We find that, even for our largest outburst, the mass contribution to the Stream is still quite small, as much of the outflow-turned-halo gas is shielded on the LMC's far-side due to the LMC's primarily face-on infall through the Milky Way halo over the past Gyr. On the LMC's near-side, past outflows have fought an uphill battle against ram pressure, with near-side halo mass being at least a factor of a few smaller than the far-side. Absorption line studies probing only the LMC foreground, then, may be severely underestimating the total mass of the LMC halo formed by outflows.
Airborne Laser Scanning (ALS) point clouds have complex structures, and their 3D semantic labeling has been a challenging task. It has three problems: (1) the difficulty of classifying point clouds around boundaries of objects from different classes, (2) the diversity of shapes within the same class, and (3) the scale differences between classes. In this study, we propose a novel double self-attention convolutional network called the DAPnet. The double self-attention includes the point attention module (PAM) and the group attention module (GAM). For problem (1), the PAM can effectively assign different weights based on the relevance of point clouds in adjacent areas. Meanwhile, for the problem (2), the GAM enhances the correlation between groups, i.e., grouped features within the same classes. To solve the problem (3), we adopt a multiscale radius to construct the groups and concatenate extracted hierarchical features with the output of the corresponding upsampling process. Under the ISPRS 3D Semantic Labeling Contest dataset, the DAPnet outperforms the benchmark by 85.2\% with an overall accuracy of 90.7\%. By conducting ablation comparisons, we find that the PAM effectively improves the model than the GAM. The incorporation of the double self-attention module has an average of 7\% improvement on the pre-class accuracy. Plus, the DAPnet consumes a similar training time to those without the attention modules for model convergence. The DAPnet can assign different weights to features based on the relevance between point clouds and their neighbors, which effectively improves classification performance. The source codes are available at: https://github.com/RayleighChen/point-attention.
Given positive integers a,b,c and d such that c and d are coprime we show that the primes p=c(mod d)dividing a^k+b^k for some k>=1 have a natural density and explicitly compute this density.   We demonstrate our results by considering some claims of Fermat that he made in a 1641 letter to Mersenne.
One of the most striking non-classical features of quantum mechanics is in the correlations it predicts between spatially separated measurements. In local hidden variable theories, correlations are constrained by Bell inequalities, but quantum correlations violate these. However, experimental imperfections lead to "loopholes" whereby LHV correlations are no longer constrained by Bell inequalities, and violations can be described by LHV theories. For example, loopholes can emerge through selective detection of events. In this letter, we introduce a clean, operational picture of multi-party Bell tests, and show that there exists a non-trivial form of loophole-free post-selection. Surprisingly, the same post-selection can enhance quantum correlations, and unlock a connection between non-classical correlations and non-classical computation.
We use integration by parts formulas to give estimates for the $L^p$ norm of the Riesz transform. This is motivated by the representation formula for conditional expectations of functionals on the Wiener space already given in Malliavin and Thalmaier. As a consequence, we obtain regularity and estimates for the density of non degenerated functionals on the Wiener space. We also give a semi-distance which characterizes the convergence to the boundary of the set of the strict positivity points for the density.
We discuss the symmetry of NaV2O5 in the high temperature phase on the basis of optical conductivity data. Conclusive information cannot be obtained by studying the optically allowed lattice vibrations. However, intensity and polarization of the electronic excitations give a direct indication for a broken-parity electronic ground-state. This is responsible for the detection of charged bi-magnons in the optical spectrum.
We extend the high-momentum antisymmetrized molecular dynamics (HMAMD) by incorporating the short-range part of the unitary correlation operator method (UCOM) as the variational method of finite nuclei. In this HMAMD+UCOM calculation of light nuclei, the HMAMD is mainly in charge of the tensor correlation with up to the four-body correlation, while the short-range correlation is further improved by using the UCOM. The binding energies of the 3H and 4He nuclei are calculated with this HMAMD+UCOM using the AV8' bare nucleon-nucleon (NN) interaction. The different roles of the short-range and tensor correlations from the HMAMD and UCOM are analyzed in the numerical results. Compared with the previous calculations based on the different variational methods, this newly extended HMAMD+UCOM method can almost provide the consistent results with the ab initio results.
Coherent optical control of individual particles has been demonstrated both for atoms and semiconductor quantum dots. Here we demonstrate the emergence of quantum coherent effects in semiconductor Rydberg excitons in bulk Cu$_2$O. Due to the spectral proximity between two adjacent Rydberg exciton states, a single-frequency laser may pump both resonances with little dissipation from the detuning. As a consequence, additional resonances appear in the absorption spectrum that correspond to dressed states consisting of two Rydberg exciton levels coupled to the excitonic vacuum, forming a V-type three-level system, but driven only by one laser light source. We show that the level of pure dephasing in this system is extremely low. These observations are a crucial step towards coherently controlled quantum technologies in a bulk semiconductor.
We present a theoretical study of Ge-core/Si-shell nanocrystals in a wide bandgap matrix and compare the results with experimental data obtained from the samples prepared by co-sputtering. The empirical tight-binding technique allows us to account for the electronic structure under strain on the atomistic level. We find that a Si shell as thick as 1 monolayer is enough to reduce the radiative recombination rate as a result of valley $L - X$ cross-over. Thin Si shell leads to a dramatic reduction of the optical bandgap from visible to near-infrared range, which is promising for photovoltaics and photodetector applications. Our detailed analysis of the structure of the confined electron and hole states in real and reciprocal spaces indicates that the type-II heterostructure is not yet achieved for Si shells with the thickness below 0.8 nm, despite some earlier theoretical predictions. The energy levels of holes are affected by the Si shell stronger than the electron states, even though holes are completely confined to the Ge core. This occurs probably due to a strong influence of strain on the band offsets.
We have studied ballistic transport in a 1D channel formed using surface gate techniques on a back-gated, high-mobility, bilayer 2D hole system. At millikelvin temperatures, robust conductance quantization is observed in the quantum wire formed in the top layer of the bilayer system, without the gate instabilities that have hampered previous studies of 1D hole systems. Using source drain bias spectroscopy, we have measured the 1D subband spacings, which are 5-10 times smaller than in comparable GaAs electron systems, but 2-3 times larger than in previous studies of 1D holes. We also report the first observation of the anomalous conductance plateau at G = 0.7 x 2e2/h in a 1D hole system.
The size distribution of ionized regions during the epoch of reionization -- a key ingredient in understanding the HI power spectrum observable by 21cm experiments -- can be modelled analytically using the excursion set formalism of random walks in the smoothed initial density field. To date, such calculations have been based on simplifying assumptions carried forward from the earliest excursion set models of two decades ago. In particular, these models assume that the random walks have uncorrelated steps and that haloes can form at arbitrary locations in the initial density field. We extend these calculations by incorporating recent technical developments that allow us to (a) include the effect of correlations in the steps of the walks induced by a realistic smoothing filter and (b) more importantly, account for the fact that dark matter haloes preferentially form near peaks in the initial density. A comparison with previous calculations shows that including these features, particularly the peaks constraint on halo locations, has large effects on the size distribution of the HII bubbles surrounding these haloes. For example, when comparing models at the same value of the globally averaged ionized volume fraction, the typical bubble sizes predicted by our model are more than a factor 2 larger than earlier calculations. Our results can potentially have a significant impact on estimates of the observable HI power spectrum.
Motivated by the recent investigation of a predator-prey model in heterogeneous environments \cite{LouYuan-WangBiao}, we show that the maximum of the unique positive solution of the scalar equation \begin{equation}\label{eq:01}\begin{cases} \mu\Delta\theta+(m(x)-\theta)\theta=0 \hspace{0.5em} &\text{in}\hspace{0.5em}\Omega,\\ \frac{\partial \theta}{\partial n}=0 \hspace{0.5em} &\text{on}\hspace{0.5em}\partial\Omega \end{cases}\end{equation} is a strictly monotone decreasing function of the diffusion rate $\mu$ for several classes of function $m$, which substantially improves a result in \cite{LouYuan-WangBiao}. However, the minimum of the positive solution of \eqref{eq:01} is monotone increasing under proper assumptions on the resource function, it is not always monotone increasing in the diffusion rate \cite{HeXiaoqing-NiWeiMing2016}.
We study the evolution of baryonic gas before the reionization in the lognormal (LN) model of cosmic clustering. We show that the thermal history of the universe around the reionization can roughly be divided into three epochs: 1) cold dark age $z>z_r$, in which baryon gas is neutral, and opaque to Ly$\alpha$ photons; 2) hot dark age $z_r > z> z_{gp}$, in which a predominant part of baryon gas is ionized and hot, but it is still opaque to Ly$\alpha$ photons; 3) bright age $z<z_{gp}$, in which the universe is ionized highly enough to be transparent to Ly$\alpha$ photons. In the flat cold dark matter cosmological models given by WMAP and COBE, the difference of the two redshifts $z_r - z_{gp}$ is found to be as large as $\sim 10$ with $z_r\sim 17$ and $z_{gp}\sim 7$. This reionization history naturally yields a high optical depth to the CMB $\tau_e \simeq 0.12 - 0.19$ observed by the TE polarization of the WMAP, and a low redshift $z_{gp}$ of the appearance of the Ly$\alpha$ Gunn-Peterson trough $z_{gp} \simeq 6 - 8$ in QSO's absorption spectra. The reason why the universe stays long in an ionized, yet Ly$\alpha$ opaque, stage is because the first photo-ionization heats the intergalactic gas effectively and has balanced the gravitational clustering a long period of time. Therefore, the result of a high $\tau_e$ and low $z_{gp}$ is a common feature of all the models considered. Besides the cosmological parameters, the only free parameter we used in the calculation is $N_{ion}$, the mean ionization photons produced by each baryon in collapsed objects. We take it to be 40 - 80 in the calculation.
Spectra of broad-lined Type Ic supernovae (SN Ic-BL), the only kind of SN observed at the locations of long-duration gamma-ray bursts (LGRBs), exhibit wide features indicative of high ejecta velocities (~0.1c). We study the host galaxies of a sample of 245 low-redshift (z<0.2) core-collapse SN, including 17 SN Ic-BL, discovered by galaxy-untargeted searches, and 15 optically luminous and dust-obscured z<1.2 LGRBs. We show that, in comparison with SDSS galaxies having similar stellar masses, the hosts of low-redshift SN Ic-BL and z<1.2 LGRBs have high stellar-mass and star-formation-rate densities. Core-collapse SN having typical ejecta velocities, in contrast, show no preference for such galaxies. Moreover, we find that the hosts of SN Ic-BL, unlike those of SN Ib/Ic and SN II, exhibit high gas velocity dispersions for their stellar masses. The patterns likely reflect variations among star-forming environments, and suggest that LGRBs can be used as probes of conditions in high-redshift galaxies. They may be caused by efficient formation of massive binary progenitors systems in densely star-forming regions, or, less probably, a higher fraction of stars created with the initial masses required for a SN Ic-BL or LGRB. Finally, we show that the preference of SN Ic-BL and LGRBs for galaxies with high stellar-mass and star-formation-rate densities cannot be attributed to a preference for low metal abundances but must reflect the influence of a separate environmental factor.