ShantanuT01/DACTYL-Pretraining huggingface dataset:
Studies of quasar absorption lines reveal that the low density intergalactic medium at z ~ 3 is enriched to 0.001-0.01 solar metallicity. This enrichment may have occurred in an early generation of Population III stars at redshift z >~ 10, by protogalaxies at 6 <~ z <~ 10, or by larger galaxies at 3 <~ z <~ 6. This paper addresses the third possibility by calculating the enrichment of the IGM at z >~ 3 by galaxies of baryonic mass >~ 10^8.5 solar masses. We use already completed cosmological simulations to which we add a prescription for chemical evolution and metal ejection by winds, assuming that the winds have properties similar to those observed in local starbursts and Lyman-break galaxies. Results are given for a number of representative models, and we also examine the properties of the galaxies responsible for the enrichment as well as the physical effects responsible for wind escape and propagation. We find that winds of velocity >~ 200-300 km/s are capable of enriching the IGM to the mean level observed, though many low-density regions would remain metal free. Calibrated by observations of Lyman-break galaxies, our calculations suggest that most galaxies at z >~ 3 should drive winds that can escape and propagate to large radii. The primary effect limiting the enrichment of low-density IG gas in our scenario is then the travel time from high- to low-density regions, implying that the metallicity of low-density gas is a strong function of redshift.
We seek a measure of the neutron density of 208Pb from analyses of intermediate energy nucleon elastic scattering. The pertinent model for such analyses is based on coordinate space nonlocal optical potentials obtained from model nuclear ground state densities. Those potentials give predictions of integral observables and of angular distributions which show sensitivity to the neutron density. When compared with experiment, and correlated with analyses of electron scattering data, the results suggest that 208Pb has a neutron skin thickness ~0.17 fm.
We present an effective field theory (EFT) at leading order to describe light single-$\Lambda$ hypernuclei. Owing to the weak $\Lambda$ binding and to the $\Lambda N$ short interaction range, meson exchange forces are approximated by contact interactions within a pionless EFT where the only degrees of freedom are baryons. At leading order, the $\Lambda$-nuclear interaction contains two 2-body (singlet and triplet) and three 3-body interaction terms, a total of 5 terms associated with 5 coupling strengths or low energy constants (LECs). We adopt the 2-body LECs from hyperon-nucleon scattering data and interaction models that constrain the $\Lambda N$ scattering lengths, while the 3-body LECs are adjusted using both 3-body and 4-body hypernuclear binding energies. To calculate the binding energies for A-body systems with A$>$2, we expand the wavefunctions using a correlated Gaussian basis. The stochastic variational method is employed to select the non-linear parameters. The resulting \nopieft~is then applied to calculate the $\Lambda$ separation energy in $_\Lambda^5$He, where the adjusted 3-body interactions largely resolve the known overbinding problem of $_\Lambda^5$He.
NU Ori is a massive spectroscopic and visual binary in the Orion Nebula Cluster, with 4 components: Aa, Ab, B, and C. The B0.5 primary (Aa) is one of the most massive B-type stars reported to host a magnetic field. We report the detection of a spectroscopic contribution from the C component in high-resolution ESPaDOnS spectra, which is also detected in a Very Large Telescope Interferometer (VLTI) dataset. Radial velocity (RV) measurements of the inner binary (designated Aab) yield an orbital period of 14.3027(7) d. The orbit of the third component (designated C) was constrained using both RVs and interferometry. We find C to be on a mildly eccentric 476(1) d orbit. Thanks to spectral disentangling of mean line profiles obtained via least-squares deconvolution we show that the Zeeman Stokes $V$ signature is clearly associated with C, rather than Aa as previously assumed. The physical parameters of the stars were constrained using both orbital and evolutionary models, yielding $M_{\rm Aa} = 14.9 \pm 0.5 M_\odot$, $M_{\rm Ab} = 3.9 \pm 0.7 M_\odot$, and $M_{\rm C} = 7.8 \pm 0.7 M_\odot$. The rotational period obtained from longitudinal magnetic field $\langle B_z \rangle$ measurements is $P_{\rm rot} = 1.09468(7)$ d, consistent with previous results. Modeling of $\langle B_z \rangle$ indicates a surface dipole magnetic field strength of $\sim 8$ kG. NU Ori C has a magnetic field strength, rotational velocity, and luminosity similar to many other stars exhibiting magnetospheric H$\alpha$ emission, and we find marginal evidence of emission at the expected level ($\sim$1% of the continuum).
Is wave function collapse a prediction of the Schr\"odinger equation? This unusual problem is explored in an enlarged framework of interpretation, where quantum dynamics is considered exact and its interpretation is extended to include local entanglement of two systems, including a macroscopic one. This property of local entanglement, which results directly from the Schr\"odinger equation but is unrelated with observables, is measured by local probabilities, fundamentally distinct from quantum probabilities and evolving nonlinearly. When applied to a macroscopic system and the fluctuations in its environment, local entanglement can also inject a formerly ignored species of incoherence into the quantum state of this system,. When applied to a quantum measurement, the conjunction of these two effects suggests a self-consistent mechanism of collapse, which would directly derive from the Schr\"odinger equation. (This work develops and improves significantly a previously circulated version with the same title [23])
We discuss the elementary physics of the final state Coulomb interactions in Hanbury-Brown Twiss interferometry, showing -- with explicit comparison to E877 data for $\pi^+\pi^-$ and $\pi^\pm p$ -- that the Coulomb corrections in the pair correlation function can be well understood in terms of simple classical physics. We connect the classical picture with descriptions in terms of Coulomb wave functions, and investigate the influence of the ``central'' Coulomb potential on the pair correlation function.
The proton diffractive structure function $F_2^{D(3)}$ measured in the H1 and ZEUS experiments at HERA are analysed in terms of perturbative QCD in the perspective of the QCD extrapolation to the Tevatron and the LHC. It is shown that both data sets can be well described by a QCD analysis in which point-like parton distributions, evolving according to the next-leading DGLAP equations, are assigned to the leading and sub-leading Regge exchanges. For present data from H1 and ZEUS the gluon distributions are found to be quite different and we give the corresponding sets of quark and gluon parton distributions for the Pomeron, extracted from the two experiments. An extrapolation to the Tevatron range is compared with CDF data on single diffraction. Conclusions on factorization breaking between HERA and Tevatron critically depend on whether H1 (strong violation) or ZEUS (compatibility at low $\beta$) fits are taken into account. Using the double Pomeron formulation in central diffractive dijet production we show that the Tevatron mass fraction is much sensitive to the high $\beta$ tail of the gluon in the Pomeron, suggesting a new way of handling the otherwise badly known gluon distribution in the Pomeron. Extrapolation of the fits to very high $Q^2$ are given since they will be relevant for QCD and diffraction studies at the LHC.
We present the results from a systematic search for galactic-scale, molecular (OH 119 $\mu$m) outflows in a sample of 52 Local Volume ($d < 50$ Mpc) Burst Alert Telescope detected active galactic nuclei (BAT AGN) with \emph{Herschel}-PACS. We combine the results from our analysis of the BAT AGN with the published \emph{Herschel}/PACS data of 43 nearby ($z<0.3$) galaxy mergers, mostly ultraluminous infrared galaxies (ULIRGs) and QSOs. The objects in our sample of BAT AGN have, on average, $\sim 10-100$ times lower AGN luminosities, star formation rates (SFRs), and stellar masses than those of the ULIRG and QSO sample. OH 119 $\mu$m is detected in 42 of our BAT AGN targets. Evidence for molecular outflows (i.e. OH absorption profiles with median velocities more blueshifted than $-$50 km s$^{-1}$ and/or blueshifted wings with 84-percentile velocities less than $-$300 km s$^{-1}$) is seen in only four BAT AGN (NGC~7479 is the most convincing case). Evidence for molecular inflows (i.e. OH absorption profiles with median velocities more redshifted than 50 km s$^{-1}$) is seen in seven objects, although an inverted P-Cygni profile is detected unambiguously in only one object (Circinus). Our data show that both the starburst and AGN contribute to driving OH outflows, but the fastest OH winds require AGN with quasar-like luminosities. We also confirm that the total absorption strength of OH 119 $\mu$m is a good proxy for dust optical depth as it correlates strongly with the 9.7 $\mu$m silicate absorption feature, a measure of obscuration originating in both the nuclear torus and host galaxy disk.
The off-centered "bar" of the Large Magellanic Cloud (LMC) is commonly assumed, for simplicity's sake, to lie in the same plane as the LMC disk. Relaxing this assumption to the extent allowed by the observations, we can drastically change our interpretation of the microlensing events towards the LMC. We propose that the off-centered ``bar'' in the Large Magellanic Cloud is a foreground object slightly misaligned with, and offset from, the plane of the LMC disk. The small displacement and misalignment are consequences of recent tidal interactions with the Small Magellanic Cloud and the Galaxy. This proposal, though radical, is consistent with the kinematics of the LMC and near-infrared star count maps from the DENIS and 2MASS surveys. It does not violate any of the observational limits on the depth and structure of the LMC -- in particular, the reported 25 to 50 degree inclination range of the LMC and the east-west gradient of distance moduli of standard candles. Contributions to LMC microlensing come from the mutual lensing of stars in the disk and the ``bar'', as well as self-lensing of the disk and the ``bar''. The microlensing optical depth of such configurations from self-lensing alone is comparable to the observed microlensing signal reported by the EROS and MACHO groups. Possible observations are suggested to discriminate between our misaligned, offset ``bar'' model and the conventional picture of an off-centered, planar bar.
In this paper, we prove that given a flat generically smooth morphism between smooth projective varieties with $F$-pure closed fibers, if the source space is Fano, weak Fano or a variety with the nef anti-canonical divisor, then so is the target space. We also show that relative anti-canonical divisors of generically smooth surjective nonconstant morphisms are not nef and big in arbitrary characteristic.
We present the line of sight radial velocity dispersion profile of the Sextans dwarf spheroidal galaxy (dSph), based on a sample of 88 stars extending to about 1 degree (about 1.5 kpc). Like the Draco and Ursa Minor dSphs, Sextans shows some evidence of a fall-off in the velocity dispersion at large projected radii, with significance p=0.96. Surprisingly, the dispersion at the very centre of Sextans is close to zero (with significance p=0.96). We present evidence which suggests that this latter change in the stellar kinematics coincides with changes in the stellar populations within the dSph. We discuss possible scenarios which could lead to a kinematically and photometrically distinct population at the centre of Sextans.
We give an algorithm to determine whether a kernel sheaf over a smooth projective curve over an algebraically closed field is semistable. The algorithm uses symmetric powers to make destabilizing subbundles visible as global sections.
We solve the two-component Dirac equation in the presence of a spatially one dimensional symmetric attractive cusp potential. The components of the spinor solution are expressed in terms of Whittaker functions. We compute the bound states solutions and show that, as the potential amplitude increases, the lowest energy state sinks into the Dirac sea becoming a resonance. We characterize and compute the lifetime of the resonant state with the help of the phase shift and the Breit-Wigner relation. We discuss the limit when the cusp potential reduces to a delta point interaction.
We consider a simple one dimensional stochastic model of heat transport which locally conserves both energy and momentum and which is coupled to heat reservoirs with different temperatures at its two ends. The steady state is analyzed and the model is found to obey the Fourier law with finite heat conductivity. In the infinite length limit, the steady state is described locally by an equilibrium Gibbs state. However finite size corrections to this local equilibrium state are present. We analyze these finite size corrections by calculating the on-site fluctuations of the momentum and the two point correlation of the momentum and energy. These correlations are long ranged and have scaling forms which are computed explicitly. We also introduce a multi-lane variant of the model in which correlations vanish in the steady state. The deviation from local equilibrium in this model as expressed in terms of the on-site momentum fluctuations is calculated in the large length limit.
Based on a prior determination of the $\phi$ selfenergy in a nuclear medium we perform a theoretical study of inclusive $\phi$ photoproduction in nuclei, looking at the $A$ dependence of the cross sections for different $\phi$ momenta. We find sizeable reductions in the nuclear cross sections with respect to the elementary one, using a $\phi$ selfenergy which implies a width about six times the free one at normal nuclear density. The calculations are done to match the set up for an ongoing experiment at {\it SPring8/Osaka} which should provide valuable information on the renormalization of the $\phi$ properties in nuclei.
Minimum information quantum gravity (MIQG) is a theory of quantum gravity which requires no explicit microscopic quantum structure. In this article, it is shown that the MIQG action can be derived using a more elegant and straight-forward method than in the first existence proof. The required assumptions are dramatically reduced. In particular, former assumptions referring to the existence of quantum boxes, the exact differential of the entropy variation and the role of the boundary can be omitted. Moreover, the open problem of the quantum occupation number per box is solved. Thus, the arguments in favour of MIQG become even more stringent. The remaining assumptions are 1. the principle of optimisation of the resulting per imposed degrees of freedom, 2. abstract quantum number conservation, 3. the validity of the laws of thermodynamics, 4. identification of a macroscopic parameterisation with space-time and 5. unspecific interactions. Although the requirements are reduced, all former results remain valid. In particular, all well established physics as special cases (Quantum Field Theory, QFT, and General Relativity, GR) follow and all measurable quantities may be computed.
The nickel--carbon system has received increased attention over the past years due to the relevance of nickel as a catalyst for carbon nanotube and graphene growth, where Nickel carbide intermediates may be involved or carbide interface layers form in the end. Nickel--carbon composite thin films comprising Ni$_3$C are especially interesting in mechanical sensing applications. Due to the meta-stability of nickel carbides, formation conditions and the coupling between mechanical and electrical properties are not yet well understood. Using first-principles electronic structure methods, we calculated the elastic properties of Ni$_3$C, Ni$_2$C and NiC, as well as changes in electronic properties under mechanical strain. We observe that the electronic density of states around the Fermi level does not change under the considered strains of up to 1%, which correspond to stresses up to 3GPa. Relative changes in conductivity of Ni$_3$C range up to maximum values of about 10%.
In this paper, we calculate the top quark rare decay t-ch in a supersymmetric extension of the standard model where baryon and lepton numbers are local gauge symmetries. Adopting reasonable assumptions on the parameter space, we find that the branching ratios of t-ch can reach 10^-3, which can be detected in near future.
We show that in a sample of size $n$ from a GEM$(0,\theta)$ random discrete distribution, the gaps $G_{i:n}:= X_{n-i+1:n} - X_{n-i:n}$ between order statistics $X_{1:n} \le \cdots \le X_{n:n}$ of the sample, with the convention $G_{n:n} := X_{1:n} - 1$, are distributed like the first $n$ terms of an infinite sequence of independent geometric$(i/(i+\theta))$ variables $G_i$. This extends a known result for the minimum $X_{1:n}$ to other gaps in the range of the sample, and implies that the maximum $X_{n:n}$ has the distribution of $1 + \sum_{i=1}^n G_i$, hence the known result that $X_{n:n}$ grows like $\theta\log(n)$ as $n\to\infty$, with an asymptotically normal distribution. Other consequences include most known formulas for the exact distributions of GEM$(0,\theta)$ sampling statistics, including the Ewens and Donnelly--Tavar\'e sampling formulas. For the two-parameter GEM$(\alpha,\theta)$ distribution we show that the maximal value grows like a random multiple of $n^{\alpha/(1-\alpha)}$ and find the limit distribution of the multiplier.
We consider the dynamics of a separable Continuous Time Random Walk (CTRW) when the random walker is biased by a velocity field in a uniformly growing domain. Concrete examples for such domains include growing biological cells or lipid vesicles, biofilms and tissues, but also macroscopic systems such as expanding aquifers during rainy periods, or the expanding universe. The considered CTRW can be subdiffusive, normal diffusive or superdiffusive, including the particular case of a L\'evy flight. We first consider the case of zero velocity field. In the subdiffusive case, we reveal an interesting time dependence of the kurtosis of the particle probability density function. In particular, for a suitable parameter choice, we find that the propagator, which is fat tailed at short times, may cross over to a Gaussian-like propagator. We subsequently incorporate the effect of the velocity field and derive a bi-fractional diffusion-advection equation encoding the time evolution of the particle distribution. We apply this equation to study the mixing kinetics of two diffusing pulses, whose peaks move towards each other under the action of velocity fields acting in opposite directions. This deterministic motion of the peaks, together with the diffusive spreading of each pulse, tends to increase particle mixing, thereby counteracting the peak separation induced by the domain growth. As a result of this competition, different regimes of mixing arise. In the case of L\'evy flights, apart from the non-mixing regime, one has two different mixing regimes in the long-time limit, depending on the exact parameter choice: In one of these regimes, mixing is mainly driven by diffusive spreading, while in the other mixing is controlled by the velocity fields acting on each pulse. Possible implications for encounter-controlled reactions in real systems are discussed.
We propose a new heuristic approach to integral moments of L-functions over function fields, which we demonstrate in the case of Dirichlet characters ramified at one place (the function field analogue of the moments of the Riemann zeta function, where we think of the character n^{it} as ramified at the infinite place). We represent the moment as a sum of traces of Frobenius on cohomology groups associated to irreducible representations. Conditional on a hypothesis on the vanishing of some of these cohomology groups, we calculate the moments of the L-function and they match the predictions of the Conrey-Farmer-Keating-Rubinstein-Snaith recipe.   In this case, the decomposition into irreducible representations seems to separate the main term and error term, which are mixed together in the long sums obtained from the approximate functional equation, even when it is dyadically decomposed. This makes our heuristic statement relatively simple, once the geometric background is set up. We hope that this will clarify the situation in more difficult cases like the L-functions of quadratic Dirichlet characters to squarefree modulus. There is also some hope for a geometric proof of this cohomological hypothesis, which would resolve the moment problem for these L-functions in the large degree limit over function fields.
Low-energy cosmic rays (LECRs) contribute substantially to the energy balance of the interstellar medium. They play also significant role in the heating and chemistry of gas, and, consequently, on the star formation process. Because of the slow propagation coupled with enhanced energy losses of subrelativistic particles, LECRs are concentrated around their acceleration sites. LECRs effectively interact with the ambient gas through nuclear reactions. Although these processes are energetically less effective compared to heating and ionization, they are extremely important from the point of view of nuclear de-excitation lines, which carry unique information about LECRs. We present results on production of de-excitation lines combining the numerical treatment of nuclear reactions using the code TALYS, with the propagation and energy losses of LECRs.
Before the publication of the Gaia DR2 we confirmed with RAVE and TGAS an observation recently made with the GALAH survey by Quillen ey al. concerning the Coma Berenices moving group in the Solar neighbourhood, namely that it is only present at negative Galactic latitudes. This allowed us to show that it is coherent in vertical velocity, providing a first evidence for incomplete vertical phase-mixing. We estimated for the first time from dynamical arguments that the moving group must have formed at most ~ 1.5 Gyr ago, and related this to a pericentric passage of the Sagittarius dwarf satellite galaxy. The present note is a rewritten version of the original arXiv post on this result now also including a confirmation of our finding with Gaia DR2.
Long-term visual localization is the problem of estimating the camera pose of a given query image in a scene whose appearance changes over time. It is an important problem in practice, for example, encountered in autonomous driving. In order to gain robustness to such changes, long-term localization approaches often use segmantic segmentations as an invariant scene representation, as the semantic meaning of each scene part should not be affected by seasonal and other changes. However, these representations are typically not very discriminative due to the limited number of available classes. In this paper, we propose a new neural network, the Fine-Grained Segmentation Network (FGSN), that can be used to provide image segmentations with a larger number of labels and can be trained in a self-supervised fashion. In addition, we show how FGSNs can be trained to output consistent labels across seasonal changes. We demonstrate through extensive experiments that integrating the fine-grained segmentations produced by our FGSNs into existing localization algorithms leads to substantial improvements in localization performance.