ShantanuT01/DACTYL-Pretraining huggingface dataset:
We study dynamics of antiferromagnets induced by simultaneous application of dc spin current and ac charge current, motivated by the requirement of all-electrically controlled devices in THz gap (0.1-30 THz). We show that ac electric current, via N\'eel spin orbit torques, can lock the phase of a steady rotating N\'eel vector whose precession is controlled by a dc spin current. In the phase-locking regime the frequency of the incoming ac signal coincides with the frequency of autooscillations which for typical antiferromagnets fall into the THz range. The frequency of autooscillations is proportional to the precession-induced tilting of the magnetic sublattices related to the so-called dynamical magnetization. We show how the incoming ac signal can be detected from the measurement of the dc-current dependencies of the constant dynamical magnetization. We formulate the conditions of phase-locking based on relations between parameters of an antiferromagnet and the characteristics of the incoming signal (frequency, amplitude, bandwidth, duration). We also show that the rotating N\'eel vector can generate ac electrical current via inverse N\'eel spin-orbit torque. Hence, antiferromagnets driven by dc spin current can be used as tunable detectors and emitters of narrow-band signals operating in the THz range.
The statistical mechanics of periodically driven ("Floquet") systems in contact with a heat bath exhibits some radical differences from the traditional statistical mechanics of undriven systems. In Floquet systems all quasienergies can be placed in a finite frequency interval, and the number of near degeneracies in this interval grows without limit as the dimension N of the Hilbert space increases. This leads to pathologies, including drastic changes in the Floquet states, as N increases. In earlier work these difficulties were put aside by fixing N, while taking the coupling to the bath to be smaller than any quasienergy difference. This led to a simple explicit theory for the reduced density matrix, but with some major differences from the usual time independent statistical mechanics. We show that, for weak but finite coupling between system and heat bath, the accuracy of a calculation within the truncated Hilbert space spanned by the N lowest energy eigenstates of the undriven system is limited, as N increases indefinitely, only by the usual neglect of bath memory effects within the Born and Markov approximations. As we seek higher accuracy by increasing N, we inevitably encounter quasienergy differences smaller than the system-bath coupling. We therefore derive the steady state reduced density matrix without restriction on the size of quasienergy splittings. In general, it is no longer diagonal in the Floquet states. We analyze, in particular, the behavior near a weakly avoided crossing, where quasienergy near degeneracies routinely appear. The explicit form of our results for the denisty matrix gives a consistent prescription for the statistical mechanics for many periodically driven systems with N infinite, in spite of the Floquet state pathologies.
In this paper, we introduce a generative model for image enhancement specifically for improving diver detection in the underwater domain. In particular, we present a model that integrates generative adversarial network (GAN)-based image enhancement with the diver detection task. Our proposed approach restructures the GAN objective function to include information from a pre-trained diver detector with the goal to generate images which would enhance the accuracy of the detector in adverse visual conditions. By incorporating the detector output into both the generator and discriminator networks, our model is able to focus on enhancing images beyond aesthetic qualities and specifically to improve robotic detection of scuba divers. We train our network on a large dataset of scuba divers, using a state-of-the-art diver detector, and demonstrate its utility on images collected from oceanic explorations of human-robot teams. Experimental evaluations demonstrate that our approach significantly improves diver detection performance over raw, unenhanced images, and even outperforms detection performance on the output of state-of-the-art underwater image enhancement algorithms. Finally, we demonstrate the inference performance of our network on embedded devices to highlight the feasibility of operating on board mobile robotic platforms.
We present optical photometry and spectroscopy from about a week after explosion to $\sim$272 d of an atypical Type IIP supernova, SN 2015ba, which exploded in the edge-on galaxy IC 1029. SN 2015ba is a luminous event with an absolute V-band magnitude of -17.1$\pm$0.2 mag at 50 d since explosion and has a long plateau lasting for $\sim$123 d. The distance to the SN is estimated to be 34.8$\pm$0.7 Mpc using the expanding photosphere and standard candle methods. High-velocity H-Balmer components constant with time are observed in the late-plateau phase spectra of SN 2015ba, which suggests a possible role of circumstellar interaction at these phases. Both hydrodynamical and analytical modelling suggest a massive progenitor of SN 2015ba with a pre-explosion mass of 24-26 M$_\odot$. However, the nebular spectra of SN 2015ba exhibit insignificant levels of oxygen, which is otherwise expected from a massive progenitor. This might be suggestive of the non-monotonical link between O-core masses and the zero-age main-sequence mass of pre-supernova stars and/or uncertainties in the mixing scenario in the ejecta of supernovae.
The use of instruments that record narrow band images at selected wavelengths is a common approach in solar observations. They allow the scanning of a spectral line by sampling the Stokes profiles with 2D images at each line position, but require a compromise between spectral resolution and temporal cadence. We evaluate the impact of the time-dependent acquisition of different wavelengths on the inversion of spectropolarimetric profiles from chromospheric lines during umbral flashes. Simulations of non-linear wave propagation in a sunspot were performed with the code MANCHA. Synthetic Stokes parameters in the Ca II 8542 A line in NLTE were computed for an umbral flash using the code NICOLE. Artificial profiles with the same wavelength coverage and temporal cadence from reported observations were constructed and inverted. The inferred atmospheric stratifications were compared with the original models. The inferred atmospheres provide a reasonable characterization of the thermodynamic properties of the atmosphere during most of the phases of the umbral flash. Only at the early stages of the flash, when the shock wave reaches the formation height of the line, the Stokes profiles present apparent wavelength shifts and other spurious deformations. These features are misinterpreted by the inversion code, which can return unrealistic atmospheric models from a good fit of the Stokes profiles. The misguided results include flashed atmospheres with strong downflows, even though the simulation exhibits upflows during the umbral flash, and large variations in the magnetic field strength. Our analyses validate the inversion of Stokes profiles acquired by sequentially scanning certain selected wavelengths of a line profile, even in the case of rapidly-changing events such as umbral flashes. However, the inversions are unreliable during a short period at the development phase of the flash.
Inspired by the idea of stochastic quantization proposed by Parisi and Wu, we construct the transition probability matrix which plays a central role in the renormalization group through a stochastic differential equation. By establishing the discrete time stochastic dynamics, the renormalization procedure can be characterized from the perspective of probability. Hence, we will focus on the investigation of the infinite dimensional stochastic dynamic. From the stochastic point of view, the discrete time stochastic dynamic can induce a Markov chain. Via calculating the square field operator and the Bakry-\'Emery curvature for a class of two-points functions, the local Poincar\'e inequality is established, from which the estimate of correlation functions can also be obtained. Finally, under the condition of ergodicity, by choosing the couple relationship between the system parameter $K$ and the system time $T$ properly when $T\rightarrow +\infty$, the two-points correlation functions for limit system are also estimated.
The HDO/H2O abundance ratio is thought to be a key diagnostic on the evolution of water during the star- and planet-formation process and thus on its origin on Earth. We here present millimeter-wavelength high angular resolution observations of the deeply embedded protostar NGC1333-IRAS4B from the Submillimeter Array targeting the 3(1,2)-2(2,1) transition of HDO at 225.6 GHz (Eu = 170 K). We do not (or only very tentatively) detect the HDO line toward the central protostar, contrasting the previous prominent detection of a line from another water isotopologue, H2-18-O, with similar excitation properties using the IRAM Plateau de Bure Interferometer. The non-detection of the HDO line provides a direct, model independent, upper limit to the HDO/H2O abundance ratio of 6e(-4) (3sigma) in the warm gas associated with the central protostar. This upper limit suggests that the HDO/H2O abundance ratio is not significantly enhanced in the inner 50 AU around the protostar relative to what is seen in comets and Earth's oceans and does not support previous suggestions of a generally enhanced HDO/H2O ratio in these systems.
Explosions of type Ic supernovae (SNe Ic) are investigated using a relativistic hydrodynamic code to study roles of their outermost layers of the ejecta in light element nucleosynthesis through spallation reactions as a possible mechanism of the "primary" process. We have confirmed that the energy distribution of the outermost layers with a mass fraction of only 0.001 % follows the empirical formula proposed by previous work when the explosion is furious. In such explosions, a significant fraction of the ejecta ($>$0.1 % in mass) have the energy greater than the threshold energy for spallation reactions. On the other hand, it is found that the outermost layers of ejecta become more energetic than the empirical formula would predict when the explosion energy per unit ejecta mass is smaller than $\sim 1.3\times 10^{51}{ergs/}\Msun$. As a consequence, it is necessary to numerically calculate explosions to estimate light element yields from SNe Ic. The usage of the empirical formula would overestimate the yields by a factor of $\gtsim 3$ for energetic explosions such as SN 1998bw and underestimate the yields by a similar factor for less energetic explosions like SN 1994I. The yields of light elements Li, Be, and B (LiBeB) from SNe Ic are estimated by solving the transfer equation of cosmic rays originated from ejecta of SNe Ic and compared with observations.
We study the incidence of nuclear obscuration on a complete sample of 1310 AGN selected on the basis of their rest-frame 2-10 keV X-ray flux from the XMM-COSMOS survey, in the redshift range 0.3<z<3.5. We classify the AGN as obscured or un-obscured on the basis of either the optical spectral properties and the overall SED or the shape of the X-ray spectrum. The two classifications agree in about 70% of the objects, and the remaining 30% can be further subdivided into two distinct classes: at low luminosities X-ray un-obscured AGN do not always show signs of broad lines or blue/UV continuum emission in their optical spectra, most likely due to galaxy dilution effects; at high luminosities broad line AGN may have absorbed X-ray spectra, which hints at an increased incidence of small-scale (sub-parsec) dust-free obscuration. We confirm that the fraction of obscured AGN is a decreasing function of the intrinsic X-ray luminosity, while the incidence of absorption shows significant evolution only for the most luminous AGN, which appear to be more commonly obscured at higher redshift. We find no significant difference between the mean stellar masses and star formation rates of obscured and un-obscured AGN hosts. We conclude that the physical state of the medium responsible for obscuration in AGN is complex, and mainly determined by the radiation environment (nuclear luminosity) in a small region enclosed within the gravitational sphere of influence of the central black hole, but is largely insensitive to the wider scale galactic conditions.
The Central Limit Theorem for the random walk on a stationary random network of conductances has been studied by several authors. In one dimension, when conductances and resistances are integrable, and following a method of martingale introduced by S. Kozlov (1985), we can prove the Quenched Central Limit Theorem. In that case the variance of the limit law is not null. When resistances are not integrable, the Annealed Central Limit Theorem with null variance was established by Y. Derriennic and M. Lin (personal communication). The quenched version of this last theorem is proved here, by using a very simple method. The similar problem for the continuous diffusion is then considered. Finally our method allows us to prove an inequality for the quadratic mean of a diffusion (X_t)_t at all time t.
Let $f$ be a Hecke-Maass or holomorphic primitive cusp form of arbitrary level and nebentypus, and let $\chi$ be a primitive character of conductor $M$. For the twisted $L$-function $L(s,f\otimes \chi)$ we establish the hybrid subconvex bound $$ L(1/2+it,f\otimes\chi)\ll (M(3+|t|))^{1/2-1/18+\varepsilon}, $$ for $t\in \mathbb R$. The implied constant depends only on the form $f$ and $\varepsilon$.
An extensive theoretical search for the proton magic number in the superheavy valley beyond $Z=$82 and corresponding neutron magic number after $N=$126 is carried out. For this we scanned a wide range of elements $Z=112-130$ and their isotopes. The well established non-relativistic Skryme-Hartree-Fock and Relativistic Mean Field formalisms with various force parameters are used. Based on the calculated systematics of pairing gap, two neutron separation energy and the shell correction energy for these nuclei, we find $Z=$120 as the next proton magic and N=172, 182/184, 208 and 258 the subsequent neutron magic numbers.
Visual feature clustering is one of the cost-effective approaches to segment objects in videos. However, the assumptions made for developing the existing algorithms prevent them from being used in situations like segmenting an unknown number of static and moving objects under heavy camera movements. This paper addresses the problem by introducing a clustering approach based on superpixels and short-term Histogram of Oriented Optical Flow (HOOF). Salient Dither Pattern Feature (SDPF) is used as the visual feature to track the flow and Simple Linear Iterative Clustering (SLIC) is used for obtaining the superpixels. This new clustering approach is based on merging superpixels by comparing short term local HOOF and a color cue to form high-level semantic segments. The new approach was compared with one of the latest feature clustering approaches based on K-Means in eight-dimensional space and the results revealed that the new approach is better by means of consistency, completeness, and spatial accuracy. Further, the new approach completely solved the problem of not knowing the number of objects in a scene.
The integer $\beta (\rho, v, k)$ is defined to be the maximum number of blocks in any $(v, k)$-packing in which the maximum partial parallel class (or PPC) has size $\rho$. This problem was introduced and studied by Stinson for the case $k=3$. Here, we mainly consider the case $k = 4$ and we obtain some upper bounds and lower bounds on $\beta (\rho, v, 4)$. We also provide some explicit constructions of $(v,4)$-packings having a maximum PPC of a given size $\rho$. For small values of $\rho$, the number of blocks of the constructed packings are very close to the upper bounds on $\beta (\rho, v, 4)$. Some of our methods are extended to the cases $k > 4$.
We discuss an equivalence relation on the set of square binary matrices with the same number of 1's in each row and each column. Each binary matrix is represented using ordered n-tuples of natural numbers. We give a few starting values of integer sequences related to the discussed problem. The obtained sequences are new and they are not described in the On-Line Encyclopedia of Integer Sequences (OEIS). We show a relationship between some particular values of the parameters and the Fibonacci sequence.
We present a method for stabilizing handheld video that simulates the camera motions cinematographers achieve with equipment like tripods, dollies, and Steadicams. We formulate a constrained convex optimization problem minimizing the $\ell_1$-norm of the first three derivatives of the stabilized motion. Our approach extends the work of Grundmann et al. [9] by solving with full homographies (rather than affinities) in order to correct perspective, preserving linearity by working in log-homography space. We also construct crop constraints that preserve field-of-view; model the problem as a quadratic (rather than linear) program to allow for an $\ell_2$ term encouraging fidelity to the original trajectory; and add constraints and objectives to reduce distortion. Furthermore, we propose new methods for handling salient objects via both inclusion constraints and centering objectives. Finally, we describe a windowing strategy to approximate the solution in linear time and bounded memory. Our method is computationally efficient, running at 300fps on an iPhone XS, and yields high-quality results, as we demonstrate with a collection of stabilized videos, quantitative and qualitative comparisons to [9] and other methods, and an ablation study.
The forerunners preceding the main tunneling signal of the wave created by a source with a sharp onset or by a quantum shutter, have been generally associated with over-the-barrier (non-tunneling) components. We demonstrate that, while this association is true for distances which are larger than the penetration lenght, for smaller distances the forerunner is dominated by under-the-barrier components. We find that its characteristic arrival time is inversely proportional to the difference between the barrier energy and the incidence energy, a tunneling time scale different from both the phase time and the B\"uttiker-Landauer (BL) time.
We consider the heat equation with a logarithmic nonlinearity, on thereal line. For a suitable sign in front of the nonlinearity, weestablish the existence and uniqueness of solutions of the Cauchyproblem, for a well-adapted class of initial data. Explicitcomputations in the case of Gaussian data lead to various scenariiwhich are richer than the mere comparison with the ODE mechanism,involving (like in the ODE case) double exponential growth or decayfor large time. Finally, we prove that such phenomena remain, in the case of compactlysupported initial data.
The rate of the nuclear reaction $^3He+\mu^- \to ^3H+\gamma+\nu_{\mu}$ has been calculated using both the elementary particle model (EPM) approach and the impulse approximation (IA) approach. Using the EPM approach, the exclusive statistical radiative muon capture (RMC) rate for photon energy greater than 57 MeV is found to be $0.245 s^{-1}$ and the ordinary muon capture (OMC) rate to be $1503 s^{-1}$. The IA calculation exhibits a slight dependence on the type of trinucleon wave functions used. The difference between the IA and EPM calculation is larger for RMC than for OMC. To resolve the difference between the two approaches a more detailed investigation including meson exchange corrections will be required.
A number of studies have investigated the training of neural networks with synthetic data for applications in the real world. The aim of this study is to quantify how much real world data can be saved when using a mixed dataset of synthetic and real world data. By modeling the relationship between the number of training examples and detection performance by a simple power law, we find that the need for real world data can be reduced by up to 70% without sacrificing detection performance. The training of object detection networks is especially enhanced by enriching the mixed dataset with classes underrepresented in the real world dataset. The results indicate that mixed datasets with real world data ratios between 5% and 20% reduce the need for real world data the most without reducing the detection performance.
Aims. The interaction of supernova remnants (SNRs) with molecular clouds gives rise to strong molecular emission in the far-IR and sub-mm wavelength regimes. The application of MHD shock models in the interpretation of this line emission can yield valuable information on the energetic and chemical impact of supernova remnants. Methods. New mapping observations with the APEX telescope in CO (3-2), (4-3), (6-5), (7-6) and 13CO (3-2) towards two regions in the supernova remnant W44 are presented. Integrated intensities are extracted on five different positions, corresponding to local maxima of CO emission. The integrated intensities are compared to the outputs of a grid of models, which combine an MHD shock code with a radiative transfer module based on the large velocity gradient approximation. Results. All extracted spectra show ambient and line-of-sight components as well as blue- and red-shifted wings indicating the presence of shocked gas. Basing the shock model fits only on the highest-lying transitions that unambiguously trace the shock-heated gas, we find that the observed CO line emission is compatible with non-stationary shocks and a pre-shock density of 10^4 cm-3. The ages of the modelled shocks scatter between values of \sim1000 and \sim3000 years. The shock velocities in W44F are found to lie between 20 and 25 km/s, while in W44E fast shocks (30-35 km/s) as well as slower shocks (\sim20 km/s) are compatible with the observed spectral line energy diagrams. The pre-shock magnetic field strength components perpendicular to the line of sight in both regions have values between 100 and 200 \muG. Our best-fitting models allow us to predict the full ladder of CO transitions, the shocked gas mass in one beam as well as the momentum- and energy injection.
Generative adversarial networks achieve great performance in photorealistic image synthesis in various domains, including human images. However, they usually employ latent vectors that encode the sampled outputs globally. This does not allow convenient control of semantically-relevant individual parts of the image, and is not able to draw samples that only differ in partial aspects, such as clothing style. We address these limitations and present a generative model for images of dressed humans offering control over pose, local body part appearance and garment style. This is the first method to solve various aspects of human image generation such as global appearance sampling, pose transfer, parts and garment transfer, and parts sampling jointly in a unified framework. As our model encodes part-based latent appearance vectors in a normalized pose-independent space and warps them to different poses, it preserves body and clothing appearance under varying posture. Experiments show that our flexible and general generative method outperforms task-specific baselines for pose-conditioned image generation, pose transfer and part sampling in terms of realism and output resolution.
Deviations of the observed cosmic microwave background (CMB) from the standard model, known as "anomalies", are obviously highly significant and deserve to be pursued more aggressively in order to discover the physical phenomena underlying them. Through intensive investigation we have discovered that there are equally surprising features in the digits of the number $\pi$, and moreover there is a remarkable correspondence between each type of peculiarity in the digits of $\pi$ and the anomalies in the CMB. Putting aside the unreasonable possibility that these are just the sort of flukes that appear when one looks hard enough, the only conceivable conclusion is that, however the CMB anomalies were created, a similar process imprinted patterns in the digits of $\pi$.