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We investigate a tilted fluid component on a Bianchi V geometry in the theories of General Relativity (GR) and Quadratic Gravity (QG). The numerical time evolution is to the future. As is well known, QG contains the Ruzmaikina-Ruzmaikin (RR) solution. This solution describes the slow-roll regime of Starobinsky's inflationary model, which is currently the best one due to the excellent agreement with Cosmic Microwave Background Radiation (CMBR) data. In QG, we found universes that can be attracted to the RR solution or recollapse toward the isotropic singularity attractor. If the Equation of State (EoS) parameter is ultra-radiative w>1/3, the tilt variable increases both in RR and Milne for QG or GR, respectively. In both cases, the fluid expansion and acceleration diverge, while the vorticity initially increases and then decreases to zero., Comment: 22 pages, 9 figures

In this work, tilted source solutions in both Einstein-Hilbert General Relativity (GR) and Quadratic Gravity (QG) for the anisotropic Bianchi V model are addressed. Since the excellent CMBR match of Starobinsky's inflation with Planck's team measurements data, QG has acquired a prominent status in the effective sense, for sufficiently strong gravity fields. The main interest is in the numeric time evolution to the past towards the singularity and the behavior of the kinematic variables, vorticity, acceleration, and the expansion of this source substance. In QG we found that for universes with higher and smaller matter densities fall into the Kasner or isotropic singularity attractors to the past, respectively. We also found that the Kasner singularity attractor to the past has always zero vorticity, for both GR and QG theories. While for QG the isotropic singularity attractor may have divergent vorticity. For the set of assumptions and conditions supposed in this work, the isotropic singularity attractor, favors QG as compared to GR. Only in QG we were able to find a geometric singularity with divergences in all of the kinematic variables of the substance, decreasing to finite values to the future, upon time reversing. That is, we obtained an initial kinematic singularity substance, that approaches a perfect fluid source., Comment: 28 pages, 12 figures

We have found numerically initial conditions in the $(R, H)$ plane leading to a successful Starobinsky inflation in $R+R^2$ gravity for a isotropic metrics with positive spatial curvature. Trajectories can reach inflation regime either directly or going through a bounce, and even recollapse followed by a bounce. Our numerical plots indicate that ``good" initial conditions exist even for big initial spatial curvature, however, we argue that such a trajectory must cross a region of rather big $R$ or $H$. This means that the range of viability of $R+R^2$ theory in the $(R,H)$ plane directly affect the question of viability of Starobinsky inflation for a positive spatial curvature isotropic Universe., Comment: In this new version we have included 3 references

ESA's Rosetta spacecraft at comet 67P/Churyumov-Gerasimenko (67P) was the first mission that accompanied a comet over a substantial fraction of its orbit. On board was the ROSINA mass spectrometer suite to measure the local densities of the volatile species sublimating from the ices inside the comet's nucleus. Understanding the nature of these ices was a key goal of Rosetta. We analyzed the primary cometary molecules at 67P, namely H$_2$O and CO$_2$, together with a suite of minor species for almost the entire mission. Our investigation reveals that the local abundances of highly volatile species, such as CH$_4$ and CO, are reproduced by a linear combination of both H$_2$O and CO$_2$ densities. These findings bear similarities to laboratory-based temperature programmed desorption experiments of amorphous ices and imply that highly volatile species are trapped in H$_2$O and CO$_2$ ices. Our results do not show the presence of ices dominated by these highly volatile molecules. Most likely, they were lost due to thermal processing of 67P's interior prior to its deflection to the inner solar system. Deviations in the proportions co-released with H$_2$O and CO$_2$ can only be observed before the inbound equinox, when the comet was still far from the sun and the abundance of highly volatile molecules associated with CO$_2$ outgassing were lower. The corresponding CO$_2$ is likely seasonal frost, which sublimated and lost its trapped highly volatile species before re-freezing during the previous apparition. CO, on the other hand, was elevated during the same time and requires further investigation., Comment: This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The version of record is available online at: https://doi.org/10.1093/mnras/stad3005

The European Space Agency's Rosetta mission to comet 67P/Churyumov-Gerasimenko has offered scientists the opportunity to study a comet in unprecedented detail. Four instruments of the Rosetta orbiter, namely, the Micro-Imaging Dust Analysis System (MIDAS), the Grain Impact Analyzer and Dust Accumulator (GIADA), the COmetary Secondary Ion Mass Analyser (COSIMA), and the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) have provided information on cometary dust particles. Cross-instrument comparisons are crucial to characterize cometary dust particles beyond the capabilities of individual sensors, as they are sensitive to different dust components. We present the first comparison between detections of the ROSINA COmet Pressure Sensor (COPS) and GIADA. These two instruments are complementary as the former is sensitive solely to volatiles of icy particles, while the latter measured the dust particle as a whole, including refractories and condensed (semi)volatiles. Our goal is to correlate the particles detected by COPS and GIADA and to assess whether they belong to a common group. We statistically analyzed the in situ data of COPS and GIADA by calculating Pearson correlation coefficients. Among the several types of particles detected by GIADA, we find that COPS particles are significantly correlated solely with GIADA fluffy agglomerates (Pearson correlation coefficient of 0.55 and p-value of $4.6\cdot 10^{-3}$). This suggests that fluffy particles are composed of both refractories and volatiles. COPS volatile volumes, which may be represented by equivalent spheres with a diameter in the range between 0.06 $\mu$m and 0.8 $\mu$m, are similar to the sizes of the fractal particle's subunits identified by MIDAS (i.e., 0.05-0.18 $\mu$m)., Comment: 6 pages, 3 figures, accepted for publication in A&A

We report high-resolution, high-cadence observations of five small-scale coronal jets in an on-disk quiet Sun region observed with Solar Orbiter's EUI/\hri\ in 174 \AA. We combine the \hri\ images with the EUV images of SDO/AIA and investigate magnetic setting of the jets using co-aligned line-of-sight magnetograms from SDO/HMI. The \hri\ jets are miniature versions of typical coronal jets as they show narrow collimated spires with a base brightening. Three out of five jets result from a detectable minifilament eruption following flux cancelation at the neutral line under the minifilament, analogous to coronal jets. To better understand the physics of jets, we also analyze five small-scale jets from a high-resolution Bifrost MHD simulation in synthetic \FeIX/\FeX\ emissions. The jets in the simulation reside above neutral lines and four out of five jets are triggered by magnetic flux cancelation. The temperature maps show the evidence of cool gas in the same four jets. Our simulation also shows the signatures of opposite Doppler shifts (of the order of $\pm$10s of \kms) in the jet spire, which is evidence of untwisting motion of the magnetic field in the jet spire. The average jet duration, spire length, base width, and speed in our observations (and in synthetic \FeIX/\FeX\ images) are 6.5$\pm$4.0 min (9.0$\pm$4.0 min), 6050$\pm$2900 km (6500$\pm$6500 km), 2200$\pm$850 km, (3900$\pm$2100 km), and 60$\pm$8 \kms\ (42$\pm$20 \kms), respectively. Our observation and simulation results provide a unified picture of small-scale solar coronal jets driven by magnetic reconnection accompanying flux cancelation. This picture also aligns well with the most recent reports of the formation and eruption mechanisms of larger coronal jets., Comment: 15 pages, 9 Figures, 1 Table, Accepted for publication in ApJ

A key goal of the Solar Orbiter mission is to connect elemental abundance measurements of the solar wind enveloping the spacecraft with EUV spectroscopic observations of their solar sources, but this is not an easy exercise. Observations from previous missions have revealed a highly complex picture of spatial and temporal variations of elemental abundances in the solar corona. We have used coordinated observations from Hinode and Solar Orbiter to attempt new abundance measurements with the SPICE (Spectral Imaging of the Coronal Environment) instrument, and benchmark them against standard analyses from EIS (EUV Imaging Spectrometer). We use observations of several solar features in AR 12781 taken from an Earth-facing view by EIS on 2020 November 10, and SPICE data obtained one week later on 2020 November 17; when the AR had rotated into the Solar Orbiter field-of-view. We identify a range of spectral lines that are useful for determining the transition region and low coronal temperature structure with SPICE, and demonstrate that SPICE measurements are able to differentiate between photospheric and coronal Mg/Ne abundances. The combination of SPICE and EIS is able to establish the atmospheric composition structure of a fan loop/outflow area at the active region edge. We also discuss the problem of resolving the degree of elemental fractionation with SPICE, which is more challenging without further constraints on the temperature structure, and comment on what that can tell us about the sources of the solar wind and solar energetic particles., Comment: To be published in The Astrophysical Journal

Isotopic abundances in comets are key to understanding the history and origin of material in the Solar System. Deuterium-to-hydrogen (D/H) ratios in water are available for several comets. However, no long-term studies of the D/H ratio in water of a comet during its passage around the Sun have been reported. Linear alkanes are important organic molecules, which have been found on several Solar System bodies, including comets. To date, only upper limits of isotopic ratios for D/H and 13C/12C in linear alkanes are available. The aim of this work is a detailed analysis of the D/H ratio in water during the whole Rosetta mission. In addition, a first determination of the D/H and 13C/12C ratios in the first four linear alkanes in the coma of 67P/Churyumov-Gerasimenko is provided. We analysed in situ measurements from the Rosetta/ROSINA Double Focusing Mass Spectrometer (DFMS). The D/H ratio from HDO/H2O and the 16O/17O ratio from H216O/H217O did not change during 67P's passage around the Sun between 2014 and 2016. All D/H ratio measurements were compatible, within 1$\sigma$, with the mean value of $5.01\times10^{-4}$ and its relative variation of 2.0%. This suggests that the D/H ratio in 67P's coma is independent of heliocentric distance, level of cometary activity, as well as spacecraft location with respect to the nucleus. Additionally, the 16O/17O ratio could be determined with a higher accuracy than previously possible, yielding a value of 2347 with a relative variation of 2.3%. For the alkanes, the D/H ratio is between 4.1 and 4.8 times higher than in H2O, while the 13C/12C ratio is compatible, within uncertainties, with data for other Solar System objects. The relatively high D/H ratio in alkanes is in line with other cometary organic molecules and suggests that these organics may be inherited from the presolar molecular cloud from which the Solar System formed., Comment: Accepted for publication in A&A

Results. We found that gas-phase silicon was present throughout the Rosetta mission. Furthermore, the presence of sodium and iron atoms near the comet's perihelion confirms that sputtering cannot be the sole release process for refractory elements into the gas phase. Nickel was found to be below the detection limit. The search for parent species of any of the identified gas phase refractories has not been successful. Upper limits for a suite of possible fragment species (SiH, SiC, NaH, etc.) of larger parent and daughter species have been obtained. Furthermore, Si did not exhibit the same drop in signal as do common cometary gases when the spacecraft is pointed away from the nucleus. The combined results suggest that a direct release of elemental species from small grains on the surface of the nucleus or from small grains in the surrounding coma is a more likely explanation than the previous assumption of release via the dissociation of gaseous parent molecules., Comment: Accepted for publication in A&A

Coreference resolution is essential for automatic text understanding to facilitate high-level information retrieval tasks such as text summarisation or question answering. Previous work indicates that the performance of state-of-the-art approaches (e.g. based on BERT) noticeably declines when applied to scientific papers. In this paper, we investigate the task of coreference resolution in research papers and subsequent knowledge graph population. We present the following contributions: (1) We annotate a corpus for coreference resolution that comprises 10 different scientific disciplines from Science, Technology, and Medicine (STM); (2) We propose transfer learning for automatic coreference resolution in research papers; (3) We analyse the impact of coreference resolution on knowledge graph (KG) population; (4) We release a research KG that is automatically populated from 55,485 papers in 10 STM domains. Comprehensive experiments show the usefulness of the proposed approach. Our transfer learning approach considerably outperforms state-of-the-art baselines on our corpus with an F1 score of 61.4 (+11.0), while the evaluation against a gold standard KG shows that coreference resolution improves the quality of the populated KG significantly with an F1 score of 63.5 (+21.8)., Comment: Accepted for publication in 43rd European Conference on Information Retrieval (ECIR), 2021

In this work, the divergence and curl operators are obtained using the coordinate free non rigid basis formulation of differential geometry. Although the authors have attempted to keep the presentation self-contained as much as possible, some previous exposure to the language of differential geometry may be helpful. In this sense the work is aimed to late undergraduate or beginners graduate students interested in mathematical physics. To illustrate the development, we graphically present the eleven coordinate systems in which the Laplace operator is separable. We detail the development of the basis and the connection for the cylindrical and paraboloidal coordinate systems. We also present in [1] codes both in Maxima and Maple for the spherical orthonormal basis, which serves as a working model for calculations in other situations of interest. Also in [1] the codes to obtain the coordinate surfaces are given.

In this work we present an extension of the technique of the order reduction to higher perturbative approximations in an iterative fashion. The intention is also to analyze more carefully the conditions for the validity of the order reduction technique. With this in mind, a few simple situations in which the iterative order reduction converges analytically to the exact solutions are presented as examples. It is discovered that the order reduction as a perturbative iterative technique does not converge in the weak coupling limit as most of the known perturbative schemes, at least when applied to these examples. Also, considering these specific examples, the convergence of the order reduction occurs in strong coupling regimes. As a more realistic case, the order reduction is applied to Starobinsky's inflationary model is presented. It is verified that the method converges to the inflationary solution in the slow-roll regime.

We improve the pNRQCD approach to annihilation processes of heavy quarkonium and make first pNRQCD predictions for exclusive electromagnetic production of heavy quarkonium. We consider strongly coupled quarkonia, i.e., quarkonia that are not Coulombic bound states. Possible strongly coupled quarkonia include excited charmonium and bottomonium states. For these, pNRQCD provides expressions for the decay and exclusive electromagnetic production NRQCD matrix elements that depend on the wavefunctions at the origin and few universal gluon field correlators. We compute electromagnetic decay widths and exclusive production cross sections, and inclusive decay widths into light hadrons for $P$-wave quarkonia at relative order $v^2$ and leading order, respectively. We also compute the decay widths of $2S$ and $3S$ bottomonium states into lepton pairs and their ratios with the inclusive widths into light hadrons at relative order $v^2$., Comment: 50 pages, 4 figures, 12 tables, minor revisions, version published in JHEP