ShantanuT01/DACTYL-Pretraining huggingface dataset:
We consider a trapped ultra-cold gas of (non-condensed) bosons with two internal states (described by a pseudo spin) and study the stability of a longitudinal pseudo spin polarization gradient. For this purpose, we numerically solve a kinetic equation corresponding to a situation close to an experiment at JILA. It shows the presence of Castaing's instability of transverse spin polarization fluctuations at long wavelengths. This phenomenon could be used to create spontaneous transverse spin waves.
In this paper we present the most complete description as possible of the factorization of the general polar of the general member of an equisingularity class of irreducible germs of complex plane curves. Our result will refine the rough description of the factorization given by M. Merle in the 70's and it is based on a result given by E. Casas-Alvero in the 90's that describes the cluster of the singularities of such polars. By using our analysis, it will be possible to characterize all equisingularity classes of irreducible plane germs with r characteristic exponents having the exceptional behavior that the general polar of a general curve in this equisingularity class has only irreducible components with less than r characteristic exponents, generalizing a result previously obtained for r=2 by the authors.
We study how low-energy charge carriers scatter off periodic and linear graphene grain boundaries oriented along the zigzag direction with a periodicity three times greater than that of pristine graphene. These defects map the two Dirac points into the same position, and thus allow for intervalley scattering to occur. Starting from graphene's first-neighbor tight-binding model we show how can we compute the boundary condition seen by graphene's massless Dirac fermions at such grain boundaries. We illustrate this procedure for the 3-periodic pentagon-only grain boundary, and then work out the low-energy electronic scattering off this linear defect. We also compute the effective generalized potential seen by the Dirac fermions at the grain boundary region.
We report on the discovery of a peculiar Broad Absorption Line (BAL) quasar identified in our Gaia-assisted survey of red quasars. The systemic redshift of this quasar was difficult to establish due to the absence of conspicuous emission lines. Based on deep and broad BAL troughs (at least SiIV, CIV, and AlIII), a redshift of z=2.41 was established under the assumption that the systemic redshift can be inferred from the red edge of the BAL troughs. However, we observe a weak and spatially-extended emission line at 4450 AA most likely due to Lyman-alpha emission, which implies a systemic redshift of z=2.66 if correctly identified. There is also evidence for the onset of Lyman-alpha forest absorption bluewards of 4450 AA and evidence for H-alpha emission in the K-band consistent with a systemic redshift of z=2.66. If this redshift is correct, the quasar is an extreme example of a detached low-ionisation BAL quasar. The BAL lines must originate from material moving with very large velocities ranging from 22000 to 40000 km/s. To our knowledge, this is the first case of a systemic-redshift measurement based on extended Lyman-$\alpha$ emission for a BAL quasar, a method that should also be useful in cases of sufficiently distant BL Lac quasars without systemic-redshift information.
We establish the existence of a nontrivial weak solution to strongly indefinite asymptotically linear and superlinear Schr\"odinger equations. The novelty is to identify the essential relation between the spectrum of the operator and the behavior of the nonlinear term, in order to weaken the necessary assumptions to obtain a linking structure to the problem, for instance to allow zero being in the spectrum or the nonlinearity being sign-changing. Our main difficulty is to overcome the lack of monotonicity on the nonlinear term, as well, as the lack of compactness since the domain is unbounded. With this purpose, we require periodicity on $V$.
We present the complete NLO electroweak contribution to the production of diagonal squark--anti-squark pairs in proton--proton collisions. We discuss their effects for the production of squarks different from top squarks, in the SPS1a' scenario.
Deep neural network (DNN) architecture based models have high expressive power and learning capacity. However, they are essentially a black box method since it is not easy to mathematically formulate the functions that are learned within its many layers of representation. Realizing this, many researchers have started to design methods to exploit the drawbacks of deep learning based algorithms questioning their robustness and exposing their singularities. In this paper, we attempt to unravel three aspects related to the robustness of DNNs for face recognition: (i) assessing the impact of deep architectures for face recognition in terms of vulnerabilities to attacks inspired by commonly observed distortions in the real world that are well handled by shallow learning methods along with learning based adversaries; (ii) detecting the singularities by characterizing abnormal filter response behavior in the hidden layers of deep networks; and (iii) making corrections to the processing pipeline to alleviate the problem. Our experimental evaluation using multiple open-source DNN-based face recognition networks, including OpenFace and VGG-Face, and two publicly available databases (MEDS and PaSC) demonstrates that the performance of deep learning based face recognition algorithms can suffer greatly in the presence of such distortions. The proposed method is also compared with existing detection algorithms and the results show that it is able to detect the attacks with very high accuracy by suitably designing a classifier using the response of the hidden layers in the network. Finally, we present several effective countermeasures to mitigate the impact of adversarial attacks and improve the overall robustness of DNN-based face recognition.
In this Letter, we report the discovery of a new bright radio transient in M82. Using the Very Large Array, we observed the nuclear region of M82 at several epochs at 22 GHz and detected a new bright radio source in this galaxy's central region. We find a flux density for this flaring source that is ~300 times larger than upper limits determined in previous observations. The flare must have started between 2007 October 29 and 2008 March 24. Over the last year, the flux density of this new source has decreased from ~100 mJy to ~11 mJy. The lightcurve (based on only three data points) can be fitted better with an exponential decay than with a power law. Based on the current data we cannot identify the nature of this transient source. However, a new radio supernova seems to be the most natural explanation. With it's flux density of more than 100 mJy, it is at least 1.5 times brighter than SN1993J in M81 at the peak of its lightcurve at 22 GHz.
Let $G$ be a quadrangulation on an orientable surface and let $g$ be a proper vertex-$4$-coloring of $G$. A face $F$ of $G$ is said to be a rainbow-face if all four distinct colors appear on its boundary. A $(c_1,c_2,c_3,c_4)$-face in $G$ is a rainbow face with colors $c_i$, $i=1,2,3,4$ on the boundary in clockwise order. We show that the number of $(c_1,c_2,c_3,c_4)$-faces in $G$ equals the number of $(c_4,c_3,c_2,c_1)$-faces. This implies in particular that the number of rainbow-faces of $G$ is even.
An increasing body of data reveals a one-to-one linear correlation between galaxy halo mass and the total mass in its globular cluster (GC) population, M_{GCS} ~ M_h^{1.03 \pm 0.03}, valid over 5 orders of magnitude. We explore the nature of this correlation for galaxies of different morphological types, and for the subpopulations of metal-poor (blue) and metal-rich (red) GCs. For the subpopulations of different metallicity we find M_{GCS}(blue) ~ M_h^{0.96 \pm 0.03} and M_{GCS}(red) ~ M_h^{1.21 \pm 0.03} with similar scatter. The numerical values of these exponents can be derived from the detailed behavior of the red and blue GC fractions with galaxy mass and provide a self-consistent set of relations. In addition, all morphological types (E, S0, S/Irr) follow the same relation, but with a second-order trend for spiral galaxies to have a slightly higher fraction of metal-rich GCs for a given mass. These results suggest that the amount of gas available for GC formation at high redshift was in nearly direct proportion to the dark-matter halo potential, in strong contrast to the markedly nonlinear behavior of total stellar mass versus halo mass. Of the few available theoretical treatments that directly discuss the formation of GCs in a hierarchical merging framework,the model of Kravtsov & Gnedin (2005) best matches these observations. They find that the blue, metal-poor GCs formed in small halos at $z > 3$ and did so in nearly direct proportion to halo mass. Similar models addressing the formation rate of the red, metal-richer GCs in the same detail and continuing to lower redshift are still needed for a comprehensive picture.
The role of the electron-phonon interaction in the Holstein-Hubbard model is investigated in the metallic phase close to the Mott transition and in the insulating Mott phase. The model is studied by means of a variational slave boson technique. At half-filling, mean-field static quantities are in good agreement with the results obtained by numerical techniques. By taking into account gaussian fluctuations, an analytic expression of the spectral density is derived in the Mott insulating phase showing that an increase of the electron-phonon coupling leads to a sensitive reduction of the Mott gap through a reduced effective repulsion. The relation of the results with recent experimental observations in strongly correlated systems is discussed.
This paper separately evaluates the effects of inclination and asymmetry of solar coronal loops on the resonant absorption of kink magnetohydrodynamic (MHD) oscillations. We modelled a typical coronal loop by a straight and axisymmetric cylindrical magnetic flux tube filled with cold plasma. We solved the dispersion relation numerically for different values of the longitudinal mass density stratification. We show that, in inclined and asymmetric loops, the frequencies and their corresponding damping rates of the fundamental and first-overtone modes of kink oscillations are smaller in comparison with semi-circular uninclined loops with the same lengths. The results also indicate that, the period ratio $P_1/P_2$, increases with increasing the inclination of the loop, but it decreases less than $2\%$ while imposing the asymmetry to each loop side, up to $9.66\%$ of the loop length. The ratio of each mode frequency to its corresponding damping rate remain unchanged approximately while the inclination or the asymmetry imposed. Hence, we conclude that these ratios are reliable for inferring the physical parameters of coronal loops and coronal medium, regardless of the loop shape or the state of its inclination. In addition, in contrast with the effect of asymmetry which is not significant on the period ratio $P_1/P_2$, when an observed oscillating loop has a smaller apex height, the state of its inclination is an important factor that should be considered, especially when the period ratio $P_1/P_2$, is taken into consideration for coronal seismology.
Topological connections in the single-streaming voids and multistreaming filaments and walls reveal a cosmic web structure different from traditional mass density fields. A single void structure not only percolates the multistream field in all the directions, but also occupies over 99 per cent of all the single-streaming regions. Sub-grid analyses on scales smaller than simulation resolution reveal tiny pockets of voids that are isolated by membranes of the structure. For the multistreaming excursion sets, the percolating structure is significantly thinner than the filaments in over-density excursion approach.   Hessian eigenvalues of the multistream field are used as local geometrical indicators of dark matter structures. Single-streaming regions have most of the zero eigenvalues. Parameter-free conditions on the eigenvalues in the multistream region may be used to delineate primitive geometries with concavities corresponding to filaments, walls and haloes.
The association of filaments with protostellar objects has made these structures a priority target in star formation studies. The datasets of the Herschel Galactic Cold Cores Key Programme allow for a statistical study of filaments with a wide range of intrinsic and environmental characteristics. Characterisation of this sample can be used to identify key physical parameters and quantify the role of environment in the formation of supercritical filaments. Filaments were extracted from fields at D<500pc with the getfilaments algorithm and characterised according to their column density profiles and intrinsic properties. Each profile was fitted with a beam-convolved Plummer-like function and quantified based on the relative contributions from the filament 'core', represented by a Gaussian, and 'wing' component, dominated by the power-law of the Plummer-like function. These parameters were examined for populations associated with different background levels. We find that filaments increase their core (Mcore) and wing (Mwing) contributions while increasing their total linear mass density (Mtot). Both components appear to be linked to the local environment, with filaments in higher backgrounds having systematically more massive Mcore and Mwing. This dependence on the environment supports an accretion-based model for filament evolution in the local neighbourhood (D<500pc). Structures located in the highest backgrounds develop the highest central Av, Mcore, and Mwing as Mtot increases with time, favoured by the local availability of material and the enhanced gravitational potential. Our results indicate that filaments acquiring a significantly massive central region with Mcore>Mcrit/2 may become supercritical and form stars. This translates into a need for filaments to become at least moderately self-gravitating in order to undergo localised star formation or become star-forming filaments.
Proofs that an arbitrary field has a separable closure are necessarily non-constructive, and separable closures are unique only up to non-canonical isomorphism. This means that the absolute Galois group of a field is defined only up to inner automorphism. Here we construct a profinite algebraic group which is an inner form of the absolute Galois group. Our construction uses no form of the axiom of choice, and the group is defined up to canonical isomorphism. We also show that the Frobenius associated with a prime of a number field unramified in an extension, which is classically defined only up to conjugation, has a uniquely-defined analogue in terms of our group. We give a construction of the category of Artin motives with coefficients in an arbitrary field, and we give an interpretation of our absolute Galois group in terms of this category.
We study non-equilibrium dynamics of integrable and non-integrable closed quantum systems whose unitary evolution is interrupted with stochastic resets, characterized by a reset rate $r$, that project the system to its initial state. We show that the steady state density matrix of a non-integrable system, averaged over the reset distribution, retains its off-diagonal elements for any finite $r$. Consequently a generic observable $\hat O$, whose expectation value receives contribution from these off-diagonal elements, never thermalizes under such dynamics for any finite $r$. We demonstrate this phenomenon by exact numerical studies of experimentally realizable models of ultracold bosonic atoms in a tilted optical lattice. For integrable Dirac-like fermionic models driven periodically between such resets, the reset-averaged steady state is found to be described by a family of generalized Gibbs ensembles (GGE s) characterized by $r$. We also study the spread of particle density of a non-interacting one-dimensional fermionic chain, starting from an initial state where all fermions occupy the left half of the sample, while the right half is empty. When driven by resetting dynamics, the density profile approaches at long times to a nonequilibrium stationary profile that we compute exactly. We suggest concrete experiments that can possibly test our theory.
In this paper we investigate the limits of control for mixed-state quantum systems. The constraint of unitary evolution for non-dissipative quantum systems imposes kinematical bounds on the optimization of arbitrary observables. We summarize our previous results on kinematical bounds and show that these bounds are dynamically realizable for completely controllable systems. Moreover, we establish improved bounds for certain partially controllable systems. Finally, the question of dynamical realizability of the bounds for arbitary partially controllable systems is shown to depend on the accessible sets of the associated control system on the unitary group U(N) and the results of a few control computations are discussed briefly.
Oxygen-isotope effects on the intrinsic resistivity have been studied in high-quality epitaxial thin films of La_{0.75}Ca_{0.25}MnO_{3} and Nd_{0.7}Sr_{0.3}MnO_{3}. We found that the residual resistivity \rho_{o} increases by about 15(3)% upon replacing ^{16}O by ^{18}O. This provides strong evidence for the presence of small or intermediate-size polarons in the metallic ferromagnetic state. Furthermore, the temperature dependent part of the resistivity at low temperatures consists of an AT^{4.5} term contributed from 2-magnon scattering, and a B\omega_{s}/\sinh^{2}(\hbar\omega_{s}/2k_{B}T) term which arises from scattering by a soft optical phonon mode. The absolute magnitudes of the coefficient A and the phonon frequency \hbar\omega_{s} for both isotope samples are in quantitative agreement with theoretical predictions.
We show how the linear "low-density theorem" of Drukarev and Levin can be extended to arbitrary positive integer power of the baryon density $\rho$. The n^th coefficient in the McLaurin expansion of the fermion condensate's $\rho$ dependence is the connected n-nucleon sigma term matrix element. We calculate the $O(\rho^2)$ coefficient in lowest-order perturbative approximation to the linear sigma model and then show how this and other terms can be iterated to arbitrarily high order. Convergence radius of the result is discussed.
We provide a mathematical analysis of appearance of the concentrations (as Dirac masses) of the solution to a Fokker-Planck system with asymmetric potentials. This problem has been proposed as a model to describe motor proteins moving along molecular filaments. The components of the system describe the densities of the different conformations of the proteins. Our results are based on the study of a Hamilton-Jacobi equation arising, at the zero diffusion limit, after an exponential transformation change of the phase function that rises a Hamilton-Jacobi equation. We consider different classes of conformation transitions coefficients (bounded, unbounded and locally vanishing).
We formulate the work output and efficiency for linear irreversible heat engines working between a finite-sized hot heat source and an infinite-sized cold heat reservoir until the total system reaches the final thermal equilibrium state with a uniform temperature. We prove that when the heat engines operate at the maximum power under the tight-coupling condition without heat leakage the work output is just half of the exergy, which is known as the maximum available work extracted from a heat source. As a consequence, the corresponding efficiency is also half of its quasistatic counterpart.
We consider finite-energy solutions to the defocusing nonlinear wave equation in two dimensional space. We prove that almost all energy moves to the infinity at almost the light speed as time tends to infinity. In addition, the inward/outward part of energy gradually vanishes as time tends to positive/negative infinity. These behaviours resemble those of free waves. We also prove some decay estimates of the solutions if the initial data decay at a certain rate as the spatial variable tends to infinity. As an application, we prove a couple of scattering results for solutions whose initial data are in a weighted energy space. Our assumption on decay rate of initial data is weaker than previous known scattering results.
The spin Hall effect (SHE) is highly promising for spintronic applications, and the design of materials with large SHE can enable ultra-low power memory technology. Recently, 5d-transition metal oxides have been shown to demonstrate a large SHE. Here we report large values of SHE in four 5d-transition metal anti-perovskites which makes these anti-perovskites promising spintronic materials. We demonstrate that these effects originate in the mixing of dx2-y2 and dxy orbitals caused by spin orbit coupling.
We provide a mirror symmetry theorem in a range of cases where the state-of-the-art techniques relying on concavity or convexity do not apply. More specifically, we work on a family of FJRW potentials named after Fan, Jarvis, Ruan, and Witten's quantum singularity theory and viewed as the counterpart of a non-convex Gromov--Witten potential via the physical LG/CY correspondence. The main result provides an explicit formula for Polishchuk and Vaintrob's virtual cycle in genus zero. In the non-concave case of the so-called chain invertible polynomials, it yields a compatibility theorem with the FJRW virtual cycle and a proof of mirror symmetry for FJRW theory.
We study perturbative renormalization of the composite operators in the $T\bar T$-deformed two-dimensional free field theories. The pattern of renormalization for the stress-energy tensor is different in the massive and massless cases. While in the latter case the canonical stress tensor is not renormalized up to high order in the perturbative expansion, in the massive theory there are induced counterterms at linear order. For a massless theory our results match the general formula derived recently in [1].
IceCube is the world's largest neutrino telescope, recently completed at the South Pole. As a proof of pointing accuracy, we look for the image of the Moon as a deficit in down-going cosmic ray muons, using techniques similar to those used in IceCube's astronomical point-source searches.
Polymer based printable organic thin film transistor (OTFT) is a viable low cost alternative to amorphous silicon based thin film transistors and possesses light-weight and flexibility advantage. In this paper, we report on the hole injecting properties of doped PANI in OLED devices using it as an anode. From these results we conclude that hole doped PANI layers can be used as a low contact resistance source and drain electrode material for polymer OTFTs.