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The Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) suite of instruments operated throughout the over two years of the Rosetta mission operations in the vicinity of comet 67P/Churyumov-Gerasimenko. It measured gas densities and composition throughout the comet's atmosphere, or coma. Here we present two-years' worth of measurements of the relative densities of the four major volatile species in the coma of the comet, H2O. CO2, CO and O2, by one of the ROSINA sub-systems called the Double Focusing Mass Spectrometer (DFMS). The absolute total gas densities were provided by the Comet Pressure Sensor (COPS), another ROSINA sub-system. DFMS is a very high mass resolution and high sensitivity mass spectrometer able to resolve at a tiny fraction of an atomic mass unit. We have analyzed the combined DFMS and COPS measurements using an inversion scheme based on spherical harmonics that solves for the distribution of potential surface activity of each species as the comet rotates, changing solar illumination, over short intervals and as the comet changes distance from the sun and orientation of its spin axis over long time intervals. We also use the surface boundary conditions derived from the inversion scheme to simulate the whole coma with our fully kinetic Direct Simulation Monte Carlo model and calculate the production rates of the four major species throughout the mission. We compare the derived production rates with revised remote sensing observations by the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) as well as with published observations from the Microwave Instrument for the Rosetta Orbiter (MIRO). Finally we use the variation of the surface production of the major species to calculate the total mass loss over the mission and, for different estimates of the dust/gas ratio, calculate the variation of surface loss over the nucleus., Comment: 144 pages, 9 figures, 8 tables, 1 supplemental table

Comets are considered to be some of the most pristine and unprocessed solar system objects accessible to in-situ exploration. Investigating their molecular and elemental composition takes us on a journey back to the early period of our solar system and possibly even further. In this work, we deduce the bulk abundances of the major volatile species in comet 67P/Churyumov-Gerasimenko, the target of the European Space Agency's Rosetta mission. The basis are measurements obtained with the ROSINA instrument suite on board the Rosetta orbiter during a suitable period of high outgassing near perihelion. The results are combined with both gas and dust composition measurements published in the literature. This provides an integrated inventory of the major elements present in the nucleus of 67P/Churyumov-Gerasimenko. Similar to comet 1P/Halley, which was visited by ESA's Giotto spacecraft in 1986, comet 67P/Churyumov-Gerasimenko also shows near-solar abundances of oxygen and carbon, whereas hydrogen and nitrogen are depleted compared to solar. Still, the degree of devolatilization is lower than that of inner solar system objects, including meteorites and the Earth. This supports the idea that comets are among the most pristine objects in our solar system., Comment: Accepted for publication in MNRAS

The nucleus of the Jupiter-family comet 67P/Churyumov-Gerasimenko was discovered to be bi-lobate in shape when the European Space Agency spacecraft Rosetta first approached it in July 2014. The bi-lobate structure of the cometary nucleus has led to much discussion regarding the possible manner of its formation and on how the composition of each lobe might compare with that of the other. During its two-year-long mission from 2014 to 2016, Rosetta remained in close proximity to 67P/Churyumov-Gerasimenko, studying its coma and nucleus in situ. Based on lobe-specific measurements of HDO and H2O performed with the ROSINA DFMS mass spectrometer on board Rosetta, the Deuterium-to-Hydrogen ratios in water from the two lobes could be compared. No appreciable difference was observed, suggesting that both lobes formed in the same region and are homogeneous in their Deuterium-to-Hydrogen ratios., Comment: 10 pages, 6 figures. Submitted to MNRAS

We find that a donor-doped band-gap material can enhance the overall high-order harmonic generation (HHG) efficiency by several orders of magnitude, compared with undoped and acceptor-doped materials. This significant enhancement, predicted by time-dependent density functional theory simulations, originates from the highest-occupied impurity state which has an isolated energy located within the band gap. The impurity-state HHG is rationalized by a three-step model, taking into account that the impurity-state electron tunnels into the conduction band and then moves according to its band structure until recombination. In addition to the improvement of the HHG efficiency, the donor-type doping results in a harmonic cutoff different from that in the undoped and acceptor-doped cases, explained by semiclassical analysis for the impurity-state HHG., Comment: 9 pages, 7 figures, REVTeX 4.1

The ROSINA mass spectrometer DFMS on board ESA's Rosetta spacecraft detected the major isotopes of the noble gases argon, krypton, and xenon in the coma of comet 67P/Churyumov-Gerasimenko. Earlier, it has been shown that xenon exhibits an isotopic composition distinct from anywhere else in the solar system. However, argon isotopes, within error, were shown to be consistent with solar isotope abundances. This discrepancy suggested an additional exotic component of xenon in comet 67P/Churyumov-Gerasimenko. Here we show that also krypton exhibits an isotopic composition close to solar. Furthermore, we found a depletion compared to solar of argon with respect to krypton and of krypton with respect to xenon, which is a necessity to postulate an addition of exotic xenon in the comet., Comment: http://advances.sciencemag.org/content/4/7/eaar6297

Future remote sensing of exoplanets will be enhanced by a thorough investigation of our solar system Ice Giants (Neptune-size planets). What can the configuration of the magnetic field tell us (remotely) about the interior, and what implications does that field have for the structure of the magnetosphere; energy input into the atmosphere, and surface geophysics (for example surface weathering of satellites that might harbour sub-surface oceans). How can monitoring of auroral emission help inform future remote observations of emission from exoplanets? Our Solar System provides the only laboratory in which we can perform in-situ experiments to understand exoplanet formation, dynamos, systems and magnetospheres., Comment: Exoplanet Science Strategy White Paper, submitted to the National Academies of Sciences, Engineering and Medicine, Space Studies Board, 9 March 2018

Using time-dependent density functional theory, high-harmonic generation (HHG) is studied in one-dimensional structures of sizes from a single nucleus up to hundreds of nuclei. The HHG cutoff is observed to extent linearly with the system size from the well known atomic HHG cutoff and is found to converge into the previously observed cutoffs for bulk solids only for large systems. A change in the response from that of single atoms or small molecules is observed from system sizes of $N$ $\approx$ 6 nuclei and becomes independent of system size at $N \gtrsim 60$. The system-size dependence of the observed HHG cutoffs is found to follow the limitations, set by the finite size solid, on the classical motion of electron-hole pairs. Because of the relation between recombination energy and electron-hole propagation length in the system, high-energy recombination events are not possible in small systems but become accessible for larger systems resulting in the change of the cutoff energies with system size. When varying the field intensity we observe that the cutoffs move linearly with the intensity even for small systems of $N\gtrsim 6$ that are far from the limit of a bulk solid., Comment: 9 pages, 6 figures

High-harmonic generation (HHG) in the two topological phases of a finite, one-dimensional, periodic structure is investigated using a self-consistent time-dependent density functional theory (TDDFT) approach. For harmonic photon energies smaller than the band gap, the harmonic yield is found to differ up to fourteen orders of magnitude for the two topological phases. This giant topological effect is explained by the degree of destructive interference in the harmonic emission of all valence-band (and edge-state) electrons, which strongly depends on whether topological edge states are present or not. The combination of strong-field laser physics with topological condensed matter opens up new possibilities to electronically control strong-field-based light or particle sources or---vice versa---to steer by all optical means topological electronics., Comment: 5 pages, 4 figures, RevTeX 4.1, Supplemental Material

High-harmonic generation by a laser-driven solid slab is simulated using time-dependent density functional theory. Multiple harmonic plateaus up to very high harmonic orders are observed already at surprisingly low field strengths. The full all-electron harmonic spectra are, in general, very different from those of any individual Kohn-Sham orbital. Freezing the Kohn-Sham potential instead is found to be a good approximation for the laser intensities and harmonic orders considered. The origins of the plateau cutoffs are explained in terms of band gaps that can be reached by Kohn-Sham electrons and holes moving through the band structure., Comment: 9 pages, 8 figures, RevTeX 4.1

We present a study of non-sequential double recombination (NSDR) high harmonic generation (HHG) in a molecular-like system. Using a Coulomb-corrected three-step model we are able to classically describe the observed NSDR HHG cutoffs precisely for all internuclear distances showing an intrinsic dependence on the location of the nuclei in the NSDR HHG process originating partly from the strong electron correlation in the NSDR HHG process. This dependence modifies the classically allowed return energies which in return changes the cutoffs observed in the HHG spectra. We also observe that the NSDR HHG signal changes its character for internuclear distances of $R\gtrsim 8-9$ a.u. which is proposed to stem from a change in the charge transfer dynamics within the molecule. For large internuclear distances of $R\gtrsim 13$ a.u. we observe a clear signature of the point of emission for the first electron emitted in the NSDR HHG signal and we also see signs of molecular exchange paths contributing to the HHG spectrum for these internuclear distances., Comment: 7 pages, 8 figures

Non-sequential double recombination (NSDR) high-order harmonic generation (HHG) is studied in a molecular system. We observe a unique molecular two-electron effect with a characteristic cutoff in the HHG spectrum at higher energies than what was previously seen for NSDR HHG in atoms. The effect is corroborated with a classical model where it is found that the effect is sensitive to the molecular potential and originates from same period emission and recombination (SPEaR) of two electrons. The effect persists for intermediate nuclear distances of $R \gtrsim 8.0$ a.u., Comment: 5 pages, 4 figures

Ways of rethinking school financial policy issues are examined in this report. This rethinking has evolved from growing recognition of two related principles: school finance as part of public finance; and policy formation as a product of commitments and constraints. Principles of public finance, commitments and constraints are described. Five policy options are offered, which include subsuming school finance within public finance, developing comprehensive databases, rearranging the sequence of school finance policy, developing an accountability system, and increasing collaboration. A conclusion is that each part of the system must compromise to a small extent and that school finance reform will not take place until actual school improvement occurs, which requires additional funding. (LMI)