ShantanuT01/DACTYL-Pretraining huggingface dataset:
Simple closed-box (CB) models of chemical evolution are extended on two respects: (i) simple closed-(box+reservoir) (CBR) models allowing gas outflow from the box into the reservoir or gas inflow into the box from the reservoir with same composition as the preexisting gas and rate proportional to the star formation rate, and (ii) simple multistage closed-(box+reservoir) (MCBR) models allowing different stages of evolution characterized by different inflow or outflow rates. The stellar initial mass function is assumed to be universal, and mass conservation holds for the whole system (box+reservoir) while it is violated for each subsystem (box and reservoir). The theoretical differential oxygen abundance distribution (TDOD) predicted by the model, under the assumption of instantaneous recycling, is a continuous broken line, where different slopes are related to different inflow rates. For an application of the model (a) a fictitious sample is built up from two distinct samples and taken as representative of the inner Galactic halo, and (b) different [O/H]-[Fe/H] empirical relations are deduced from five different samples related to different methods, and two of them are selected for determining the empirical differential oxygen abundance distribution (EDOD) with regard to the fictitious sample. In both cases the EDOD is represented, to an acceptable extent, as a continuous broken line. If the inner halo and the metal-poor bulge (after the inflow stage) are represented by the box and the reservoir, respectively, then the inner halo fractional mass (normalized to the halo) is comparable with, or exceeds by a factor up to 4, the metal-poor bulge fractional mass (normalized to the bulge), for current estimates of the halo-to-bulge mass ratio of about 0.05-0.10.
Australia Telescope Compact Array HI-line observations of the nearby dwarf galaxy NGC 1705 are presented. The data are used to trace the gravitational potential of the galaxy out to several stellar disc scale lengths. A rotation curve is derived for the system and used to generate mass models. Dark matter dominates the gravitational potential at nearly all galactocentric radii. NFW and pseudo-isothermal sphere halo parameterisations allowing for good reproductions of the observations. The models suggest NGC 1705 to have a dark matter halo that it much denser and more compact than previously thought.
We report here an experimental and theoretical study on the magnetoresistance properties of heavily phosphorous doped germanium on the metallic side of the metal-nonmetal transition. An anomalous regime, formed by negative values of the magnetoresistance, was observed by performing low-temperature measurements and explained within the generalized Drude model, due to the many-body effects. It reveals a key mechanism behind the magnetoresistance properties at low temperatures and, therefore, constitutes a path to its manipulation in such materials of great interest in fundamental physics and technological applications
In a recent e-print [cond-mat/0603260] Hall and Flatte claim that a particular spin based field effect transistor (SPINFET), which they have analyzed, will have a lower threshold voltage, lower switching energy and lower leakage current than a comparable metal oxide semiconductor field effect transistor (MOSFET). Here, we show that all three claims of HF are invalid.
In the $q$-voter model, the voter at $x$ changes its opinion at rate $f_x^q$, where $f_x$ is the fraction of neighbors with the opposite opinion. Mean-field calculations suggest that there should be coexistence between opinions if $q<1$ and clustering if $q>1$. This model has been extensively studied by physicists, but we do not know of any rigorous results. In this paper, we use the machinery of voter model perturbations to show that the conjectured behavior holds for $q$ close to 1. More precisely, we show that if $q<1$, then for any $m<\infty$ the process on the three-dimensional torus with $n$ points survives for time $n^m$, and after an initial transient phase has a density that it is always close to 1/2. If $q>1$, then the process rapidly reaches fixation on one opinion. It is interesting to note that in the second case the limiting ODE (on its sped up time scale) reaches 0 at time $\log n$ but the stochastic process on the same time scale dies out at time $(1/3)\log n$.
We present polarisation data for 180 extragalactic sources extracted from the Australia Telescope 20 GHz (AT20G) survey catalog, and observed with the Australia Telescope Compact Array during a dedicated, high sensitivity run. For the sake of completeness we extracted the polarisation information for 7 extended sources from the 9-yr WMAP coadded maps at 23 GHz. The full sample of 187 sources constitutes a 99% complete sample of extragalactic sources brighter than S(20 GHz)=500mJy at the selection epoch with declination <-30 deg. The sample has a 91.4% detection rate in polarisation at 20GHz (94% if considering the sub-sample of point like sources). We have measurements also at 4.8 and 8.6 GHz within 1 month of the 20GHz observations for 172 sources to reconstruct the spectral properties of the sample in total intensity and in polarisation: 143 of them have a polarisation detection at all three frequencies. We find that there is no statistically significant evidence of a relationship either between the fraction of polarisation and frequency or between the fraction of polarisation and the total intensity flux density. This indicates that Faraday depolarisation is not very important above 4.8 GHz and that the magnetic field is not substantially more ordered in the regions dominating the emission at higher frequencies (up to 20 GHz). We estimate the distribution of the polarisation fraction and the polarised flux density source counts at 20GHz.
We study the thermal Markovian diffusion of tracer particles in a 2D medium with spatially-varying diffusivity $D(r)$, mimicking recently measured, heterogeneous maps of the apparent diffusion coefficient in biological cells. For this heterogeneous diffusion process (HDP) we analyse the mean squared displacement (MSD) of the tracer particles, the time averaged MSD, the spatial probability density function, and the first passage time dynamics from the cell boundary to the nucleus. Moreover we examine the non-ergodic properties of this process which are important for the correct physical interpretation of time averages of observables obtained from single particle tracking experiments. From extensive computer simulations of the 2D stochastic Langevin equation we present an in-depth study of this HDP. In particular, we find that the MSDs along the radial and azimuthal directions in a circular domain obey anomalous and Brownian scaling, respectively. We demonstrate that the time averaged MSD stays linear as a function of the lag time and the system thus reveals a weak ergodicity breaking. Our results will enable one to rationalise the diffusive motion of larger tracer particles such as viruses or submicron beads in biological cells.
The nonequilibrium work fluctuation theorem provides the way for calculations of (equilibrium) free energy based on work measurements of nonequilibrium, finite-time processes and their reversed counterparts by applying Bennett's acceptance ratio method. A nice property of this method is that each free energy estimate readily yields an estimate of the asymptotic mean square error. Assuming convergence, it is easy to specify the uncertainty of the results. However, sample sizes have often to be balanced with respect to experimental or computational limitations and the question arises whether available samples of work values are sufficiently large in order to ensure convergence. Here, we propose a convergence measure for the two-sided free energy estimator and characterize some of its properties, explain how it works, and test its statistical behavior. In total, we derive a convergence criterion for Bennett's acceptance ratio method.
In this paper we present a comprehensive study of magnetic dynamics in the rare-earth orthoferrite YbFeO$_3$ at temperatures below and above the spin-reorientation (SR) transition $T_{\mathrm{SR}}=7.6$ K, in magnetic fields applied along the $a, b$ and $c$ axes. Using single-crystal inelastic neutron scattering, we observed that the spectrum of magnetic excitations consists of two collective modes well separated in energy: 3D gapped magnons with a bandwidth of $\sim$60 meV, associated with the antiferromagnetically (AFM) ordered Fe subsystem, and quasi-1D AFM fluctuations of $\sim$1 meV within the Yb subsystem, with no hybridization of those modes. The spin dynamics of the Fe subsystem changes very little through the SR transition and could be well described in the frame of semiclassical linear spin-wave theory. On the other hand, the rotation of the net moment of the Fe subsystem at $T_{\mathrm{SR}}$ drastically changes the excitation spectrum of the Yb subsystem, inducing the transition between two regimes with magnon and spinon-like fluctuations. At $T < T_{\mathrm{SR}}$, the Yb spin chains have a well defined field-induced ferromagnetic (FM) ground state, and the spectrum consists of a sharp single-magnon mode, a two-magnon bound state, and a two-magnon continuum, whereas at $T > T_{\mathrm{SR}}$ only a gapped broad spinon-like continuum dominates the spectrum. In this work we show that a weak quasi-1D coupling within the Yb subsystem $J_\text{Yb-Yb}$, mainly neglected in previous studies, creates unusual quantum spin dynamics on the low energy scales. The results of our work may stimulate further experimental search for similar compounds with several magnetic subsystems and energy scales, where low-energy fluctuations and underlying physics could be "hidden" by a dominating interaction.
Reggeon cuts in QCD amplitudes with negative signature are discussed. These cuts appear in the next-to-next-to-leading logarithmic approximation (NNLLA) and greatly complicate the derivation of the BFKL equation. Feynman diagrams responsible for appearance of these cuts are indicated and the cut contributions are calculated in the two- and three-loop approximation.
The large interest in chiral magnetic structures for realization of nanoscale magnetic storage or logic devices has necessitated methods which can quantify magnetic interactions at the atomic scale. To overcome the limitations of the typically used current-based sensing of atomic-scale exchange interactions, a force-based detection scheme is highly advantageous. Here, we quantify the atomic-scale exchange force field between a ferromagnetic tip and a cycloidal spin spiral using our developed combination of current and exchange force detection. Compared to the surprisingly weak spin polarization, the exchange force field is more sensitive to atomic-scale variations in the magnetization. First-principles calculations reveal that the measured atomic-scale variations in the exchange force originate from different contributions of direct and indirect (Zener) type exchange mechanisms, depending on the chemical tip termination. Our work opens the perspective of quantifying different exchange mechanisms of chiral magnetic structures with atomic-scale precision using 3D magnetic exchange force field measurements.
Generalized permutahedra are the polytopes obtained from the permutahedron by changing the edge lengths while preserving the edge directions, possibly identifying vertices along the way. We introduce a "lifting" construction for these polytopes, which turns an $n$-dimensional generalized permutahedron into an $(n+1)$-dimensional one. We prove that this construction gives rise to Stasheff's multiplihedron from homotopy theory, and to the more general "nestomultiplihedra," answering two questions of Devadoss and Forcey.   We construct a subdivision of any lifted generalized permutahedron whose pieces are indexed by compositions. The volume of each piece is given by a polynomial whose combinatorial properties we investigate. We show how this "composition polynomial" arises naturally in the polynomial interpolation of an exponential function. We prove that its coefficients are positive integers, and present evidence suggesting that they may also be unimodal.
We study the heavy quark effective theory prediction for semileptonic $B$ decays into an orbital excited $F$-wave charmed doublet, the ($2^{+}$, $3^{+}$) states ($D^{*'}_{2}$, $D_{3}$), at the leading order of heavy quark expansion. The corresponding universal form factor is estimated by using the QCD sum rule method. The decay rates we predict are $\Gamma_{B\to D^{*'}_{2}\ell\overline{\nu}}=1.85\times10^{-19} {GeV}$ and $\Gamma_{B\to D_{3}\ell\overline{\nu}}=1.78\times10^{-19} {GeV}$. The branching ratios are $\mathcal {B}(B\to D_{2}^{*'}\ell\overline{\nu})=4.6\times10^{-7}$ and $\mathcal {B}(B\to D_{3}\ell\overline{\nu})=4.4\times10^{-7}$, respectively.
We present the results of a systematic search for molecular hydrogen (H2) in low redshift ($ 0.05 \lesssim z \lesssim 0.7$) DLAs and sub-DLAs with $N(HI) \gtrsim 10^{19.0}$ cm$^{-2}$, in the archival HST/COS spectra. Our core sample is comprised of 27 systems with a median $\log N(HI) = 19.6$. On the average, our survey is sensitive down to $\log N(H2) = 14.4$ corresponding to a molecular fraction of $\log f_{H2} = -4.9$ at the median $N(HI)$. H2 is detected in 10 cases (3/5 DLAs and 7/22 sub-DLAs) down to this $f_{H2}$ limit. The H2 detection rate of $50^{+25}_{-12}$ percent seen in our sample, is a factor of $\gtrsim 2$ higher than that of the high-$z$ sample of Noterdaeme et al. (2008), for systems with $N(H2) > 10^{14.4}$ cm$^{-2}$. In spite of having $N(HI)$ values typically lower by a factor of 10, low-$z$ H2 systems show molecular fractions ($\log f_{H2}=-1.93\pm0.63$) that are comparable to the high-$z$ sample. The rotational excitation temperatures ($T_{01} = 133\pm55$ K), as measured in our low-$z$ sample, are typically consistent with high-$z$ measurements. Simple photoionization models favour a radiation field much weaker than the mean Galactic ISM field for a particle density in the range 10 - 100 cm$^{-3}$. The impact parameters of the identified host-galaxy candidates are in the range $10 \lesssim \rho$ (kpc) $\lesssim 80$. We, therefore, conjecture that the low-$z$ H2 bearing gas is not related to star-forming disks but stems from self-shielded, tidally stripped or ejected disk-material in the extended halo.
Probing the evolution of the universe at high redshifts with standard candles is a powerful way to discriminate dark energy models, where an open question nowadays is whether this component is constant or evolves with time. One possible source of ambiguity in this kind of analyses comes from cosmic opacity, which can mimick a dark enery behaviour. However, most tests of cosmic opacity have been restricted to the redshift range $z<2$. In this work, by using luminosity distances of gamma-ray bursts (GRBs), {given the validity of the Amati relation}, and the latest $H(z)$ data we determine constraints on the cosmic opacity at high redshifts ($z>2$) for a flat $\Lambda$CDM model. A possible degenerescence of the results with the adopted cosmological model is also investigated by considering a flat XCDM model. The limits on cosmic opacity in the redshift range $0<z<2$ are updated with type Ia supernovae (SNe Ia) from the Union2.1 sample, where we added the most distant ($z=1.713$) spectroscopically confirmed SNe Ia. From the analyses performed, we find that both SNe Ia and GRBs samples are compatible with a transparent universe at $1\sigma$ level and the results are independent of the dark energy equation of state parameter $w$.
The PT-symmetry breaking, consistent hamiltonian interactions in all $n\geq 4$ spacetime dimensions that can be added to an abelian BF model involving a set of scalar fields, two sorts of one-forms, and a system of two-forms are obtained by means of the hamiltonian deformation procedure based on local BRST cohomology. This paper enhances one of our previous works, where only PT-invariant deformations were considered. The associated coupled theory is an interacting, topological BF model exhibiting an open gauge algebra and on-shell reducibility relations.
We explore the processes that trigger local AGN and the role of these AGN in regulating star formation, using ~350 nearby galaxies observed by the mJy Imaging VLBA Exploration at 20cm (mJIVE) survey. The >10^7 K brightness temperature required for an mJIVE detection cannot be achieved via star formation alone, allowing us to unambiguously detect nearby radio AGN and study their role in galaxy evolution. Radio AGN are an order of magnitude more common in early-type galaxies (ETGs) than in their late-type counterparts. The VLBI-detected ETGs in this study have a similar stellar mass distribution to their undetected counterparts, are typically not the central galaxies of clusters and exhibit merger fractions that are significantly higher than in the average ETG. This suggests that these radio AGN (which have VLBI luminosities >10^22 W Hz^-1) are primarily fuelled by mergers, and not by internal stellar mass loss or cooling flows. Our radio AGN are a factor of ~3 times more likely to reside in the UV-optical red sequence than the average ETG. Furthermore, typical AGN lifetimes (a few 10^7 yr) are much shorter than the transit times from blue cloud to red sequence (~1.5 Gyr). This indicates that the AGN are not triggered promptly and appear several dynamical timescales into the associated star formation episode, implying that they typically couple only to residual gas, at a point where star formation has already declined significantly. While evidence for AGN feedback is strong in systems where the black hole is fed by the cooling of hot gas, AGN triggered by mergers appear not to strongly regulate the associated star formation. The inability of the AGN to rapidly quench merger-driven star formation is likely to make merging the dominant mode of star formation in nearby ETGs, in line with evidence for minor mergers being the primary driver of stellar mass growth in these systems.
Momentum Contrast (MoCo) achieves great success for unsupervised visual representation. However, there are a lot of supervised and semi-supervised datasets, which are already labeled. To fully utilize the label annotations, we propose Unified Momentum Contrast (UniMoCo), which extends MoCo to support arbitrary ratios of labeled data and unlabeled data training. Compared with MoCo, UniMoCo has two modifications as follows: (1) Different from a single positive pair in MoCo, we maintain multiple positive pairs on-the-fly by comparing the query label to a label queue. (2) We propose a Unified Contrastive(UniCon) loss to support an arbitrary number of positives and negatives in a unified pair-wise optimization perspective. Our UniCon is more reasonable and powerful than the supervised contrastive loss in theory and practice. In our experiments, we pre-train multiple UniMoCo models with different ratios of ImageNet labels and evaluate the performance on various downstream tasks. Experiment results show that UniMoCo generalizes well for unsupervised, semi-supervised and supervised visual representation learning.
Let $(L_n)_{n\geq 0}$ be the Lucas sequence given by $L_0 = 2, L_1 = 1$ and $L_{n+2} = L_{n+1}+L_n$ for $n \geq 0$. In this paper, we are interested in finding all powers of three which are sums of two Lucas numbers, i.e., we study the exponential Diophantine equation $L_n + L_m = 3^{a}$ in nonnegative integers $n, m,$ and $a$. The proof of our main theorem uses lower bounds for linear forms in logarithms, properties of continued fractions, and a version of the Baker-Davenport reduction method in Diophantine approximation.
The dynamics of an individual magnetic moment is studied through the Landau-Lifshitz equation with a periodic driving in the direction perpendicular to the applied field. For fields lower than the anisotropy field and small values of the perturbation amplitude we have observed the magnetic moment bistability. At intermediate values we have found quasiperiodic bands alternating with periodic motion. At even larger values a chaotic regime is found. When the applied field is larger than the anisotropy one, the behavior is periodic with quasiperiodic regions. Those appear periodically in the amplitude of the oscillating field. Also, even for low values of the driving force, the moment is not parallel to the applied field.
This paper addresses the question of whether there are 4D Lorentz invariant unitary quantum field theories with scale invariance but not conformal invariance. An important loophole in the arguments of Luty-Polchinski-Rattazzi and Dymarsky-Komargodski-Schwimmer-Theisen is that trace of the energy-momentum tensor $T$ could be a generalized free field. In this paper we rule out this possibility. The key ingredient is the observation that a unitary theory with scale but not conformal invariance necessarily has a non-vanishing anomaly for global scale transformations. We show that this anomaly cannot be reproduced if $T$ is a generalized free field unless the theory also contains a dimension-2 scalar operator. In the special case where such an operator is present it can be used to redefine ("improve") the energy-momentum tensor, and we show that there is at least one energy-momentum tensor that is not a generalized free field. In addition, we emphasize that, in general, large momentum limits of correlation functions cannot be understood from the leading terms of the coordinate space OPE. This invalidates a recent argument by Farnsworth-Luty-Prilepina (FLP). Despite the invalidity of the general argument of FLP, some of the techniques turn out to be useful in the present context.
We compute the arithmetic L-invariants (of Greenberg-Benois) of twists of symmetric powers of p-adic Galois representations attached to Iwahori level Hilbert modular forms (under some technical conditions). Our method uses the automorphy of symmetric powers and the study of analytic Galois representations on p-adic families of automorphic forms over symplectic and unitary groups. Combining these families with some explicit plethysm in the representation theory of GL(2), we construct global Galois cohomology classes with coefficients in the symmetric powers and provide formulae for the L-invariants in terms of logarithmic derivatives of Hecke eigenvalues.
We present the complete set of ISOPHOT observations of 3CR radio galaxies and quasars, which are contained in the ISO Data Archive, providing 75 mid- and far-infrared spectral energy distributions (SEDs) between 5 and 200 micron. For 28 sources they are supplemented with MAMBO 1.2 mm observations and for 15 sources with new submillimetre data from the SCUBA archive.   We check the orientation-dependent unified scheme, in which the powerful FR2 narrow line galaxies are quasars viewed at high inclination, so that their nuclei are hidden behind a dust torus intercepting the optical-ultraviolet AGN radiation and reemitting it in the infrared. We find that (1) both the quasars and the galaxies show a high mid- to far-infrared luminosity ratio typical for powerful AGNs and (2) -- when matched in 178 MHz luminosity -- both show the same ratio of isotropic far-infrared to isotropic 178 MHz lobe power. Therefore, from our large sample investigated here we find strong evidence for the orientation-dependent unification of the powerful FR2 galaxies with the quasars.
In this paper we prove the existence of positive ground state solution for a class of linearly coupled systems involving Kirchhoff-Schr\"odinger equations. We study the subcritical and critical case. Our approach is variational and based on minimization technique over the Nehari manifold. We also obtain a nonexistence result using a Pohozaev identity type.