New EUV Fe IX emission line identifications from Hinode/EIS

Four Fe IX transitions in the wavelength range 188--198 A are identified for the first time in spectra from the EUV Imaging Spectrometer on board the Hinode satellite. In particular the emission line at 197.86 A is unblended and close to the peak of the EIS sensitivity curve, making it a valuable diagnostic of plasma at around 800,000 K - a critical temperature for studying the interface between the corona and transition region. Theoretical ratios amongst the four lines predicted from the CHIANTI database reveal weak sensitivity to density and temperature with observed values consistent with theory. The ratio of 197.86 relative to the 171.07 resonance line of Fe IX is found to be an excellent temperature diagnostic, independent of density, and the derived temperature in the analysed data set is log T=5.95, close to the predicted temperature of maximum ionization of Fe IX.Comment: 10 pages, 3 figures, 2 tables, submitted to ApJ Letter

A New Approach To Analyzing Solar Coronal Spectra And Updated Collisional Ionization Equilibrium Calculations. II. Updated Ionization Rate Coefficients

We have re-analyzed Solar Ultraviolet Measurement of Emitted Radiation (SUMER) observations of a parcel of coronal gas using new collisional ionization equilibrium (CIE) calculations. These improved CIE fractional abundances were calculated using state-of-the-art electron-ion recombination data for K-shell, L-shell, Na-like, and Mg-like ions of all elements from H through Zn and, additionally, Al- through Ar-like ions of Fe. They also incorporate the latest recommended electron impact ionization data for all ions of H through Zn. Improved CIE calculations based on these recombination and ionization data are presented here. We have also developed a new systematic method for determining the average emission measure (EM) and electron temperature (Te ) of an isothermal plasma. With our new CIE data and a new approach for determining average EM and Te , we have re-analyzed SUMER observations of the solar corona. We have compared our results with those of previous studies and found some significant differences for the derived EM and Te . We have also calculated the enhancement of coronal elemental abundances compared to their photospheric abundances, using the SUMER observations themselves to determine the abundance enhancement factor for each of the emitting elements. Our observationally derived first ionization potential factors are in reasonable agreement with the theoretical model of Laming

CHIANTI - An atomic database for emission lines. XI. EUV emission lines of Fe VII, Fe VIII and Fe IX observed by Hinode/EIS

A detailed study of emission lines from Fe VII, Fe VIII and Fe IX observed by the EUV Imaging Spectrometer on board the Hinode satellite is presented. Spectra in the ranges 170-212 A and 246-292 A show strongly enhanced lines from the upper solar transition region (temperatures 5.4 <= log T <= 5.9) allowing a number of new line identifications to be made. Comparisons of Fe VII lines with predictions from a new atomic model reveal new plasma diagnostics, however there are a number of disagreements between theory and observation for emission line ratios insensitive to density and temperature, suggesting improved atomic data are required. Line ratios for Fe VIII also show discrepancies with theory, with the strong 185.21 and 186.60 lines under-estimated by 60-80 % compared to lines between 192 and 198 A. A newly-identified multiplet between 253.9 and 255.8 A offers excellent temperature diagnostic opportunities relative to the lines between 185-198 A, however the atomic model under-estimates the strength of these lines by factors 3-6. Two new line identifications are made for Fe IX at wavelengths 176.959 A and 177.594 A, while seven other lines between 186 and 200 A are suggested to be due to Fe IX but for which transition identifications can not be made. The new atomic data for Fe VII and Fe IX are demonstrated to significantly modify models for the response function of the TRACE 195 A imaging channel, affecting temperature determinations from this channel. The data will also affect the response functions for other solar EUV imaging instruments such as SOHO/EIT, STEREO/EUVI and the upcoming AIA instrument on the Solar Dynamics Observatory.Comment: 51 pages, submitted to Ap

Ionization Equilibrium Timescales in Collisional Plasmas

Astrophysical shocks or bursts from a photoionizing source can disturb the typical collisional plasma found in galactic interstellar media or the intergalactic medium. The spectrum emitted by this plasma contains diagnostics that have been used to determine the time since the disturbing event, although this determination becomes uncertain as the elements in the plasma return to ionization equilibrium. A general solution for the equilibrium timescale for each element arises from the elegant eigenvector method of solution to the problem of a non-equilibrium plasma described by Masai (1984) and Hughes & Helfand (1985). In general the ionization evolution of an element Z in a constant electron temperature plasma is given by a coupled set of Z+1 first order differential equations. However, they can be recast as Z uncoupled first order differential equations using an eigenvector basis for the system. The solution is then Z separate exponential functions, with the time constants given by the eigenvalues of the rate matrix. The smallest of these eigenvalues gives the scale of slowest return to equilibrium independent of the initial conditions, while conversely the largest eigenvalue is the scale of the fastest change in the ion population. These results hold for an ionizing plasma, a recombining plasma, or even a plasma with random initial conditions, and will allow users of these diagnostics to determine directly if their best-fit result significantly limits the timescale since a disturbance or is so close to equilibrium as to include an arbitrarily-long time.Comment: 4 pages, 2 figures. Accepted for publication by the Astrophysical Journa

Abstracting PROV provenance graphs:A validity-preserving approach

Data provenance is a structured form of metadata designed to record the activities and datasets involved in data production, as well as their dependency relationships. The PROV data model, released by the W3C in 2013, defines a schema and constraints that together provide a structural and semantic foundation for provenance. This enables the interoperable exchange of provenance between data producers and consumers. When the provenance content is sensitive and subject to disclosure restrictions, however, a way of hiding parts of the provenance in a principled way before communicating it to certain parties is required. In this paper we present a provenance abstraction operator that achieves this goal. It maps a graphical representation of a PROV document PG1 to a new abstract version PG2, ensuring that (i) PG2 is a valid PROV graph, and (ii) the dependencies that appear in PG2 are justified by those that appear in PG1. These two properties ensure that further abstraction of abstract PROV graphs is possible. A guiding principle of the work is that of minimum damage: the resultant graph is altered as little as possible, while ensuring that the two properties are maintained. The operator developed is implemented as part of a user tool, described in a separate paper, that lets owners of sensitive provenance information control the abstraction by specifying an abstraction policy.</p

Checking and Enforcing Security through Opacity in Healthcare Applications

The Internet of Things (IoT) is a paradigm that can tremendously revolutionize health care thus benefiting both hospitals, doctors and patients. In this context, protecting the IoT in health care against interference, including service attacks and malwares, is challenging. Opacity is a confidentiality property capturing a system's ability to keep a subset of its behavior hidden from passive observers. In this work, we seek to introduce an IoT-based heart attack detection system, that could be life-saving for patients without risking their need for privacy through the verification and enforcement of opacity. Our main contributions are the use of a tool to verify opacity in three of its forms, so as to detect privacy leaks in our system. Furthermore, we develop an efficient, Symbolic Observation Graph (SOG)-based algorithm for enforcing opacity

A new approach to analyzing solar coronal spectra and updated collisional ionization equilibrium calculations. II. Additional ionization rate coefficients

We have reanalyzed SUMER observations of a parcel of coronal gas using new collisional ionization equilibrium (CIE) calculations. These improved CIE fractional abundances were calculated using state-of-the-art electron-ion recombination data for K-shell, L-shell, Na-like, and Mg-like ions of all elements from H through Zn and, additionally, Al- through Ar-like ions of Fe. They also incorporate the latest recommended electron impact ionization data for all ions of H through Zn. Improved CIE calculations based on these recombination and ionization data are presented here. We have also developed a new systematic method for determining the average emission measure ($EM$) and electron temperature ($T_e$) of an isothermal plasma. With our new CIE data and our new approach for determining average $EM$ and $T_e$, we have reanalyzed SUMER observations of the solar corona. We have compared our results with those of previous studies and found some significant differences for the derived $EM$ and $T_e$. We have also calculated the enhancement of coronal elemental abundances compared to their photospheric abundances, using the SUMER observations themselves to determine the abundance enhancement factor for each of the emitting elements. Our observationally derived first ionization potential (FIP) factors are in reasonable agreement with the theoretical model of Laming (2008).Comment: 147 pages (102 of which are online only tables and figures). Submitted to ApJ. Version 2 is updated addressing the referee's repor

Common Representation of Information Flows for Dynamic Coalitions

We propose a formal foundation for reasoning about access control policies within a Dynamic Coalition, defining an abstraction over existing access control models and providing mechanisms for translation of those models into information-flow domain. The abstracted information-flow domain model, called a Common Representation, can then be used for defining a way to control the evolution of Dynamic Coalitions with respect to information flow

Properties of a Polar Coronal Hole During the Solar Minimum in 2007

We report measurements of a polar coronal hole during the recent solar minimum using the Extreme Ultraviolet Imaging Spectrometer on Hinode. Five observations are analyzed that span the polar coronal hole from the central meridian to the boundary with the quiet-Sun corona. We study the observations above the solar limb in the height range of 1.03-1.20 R ☉. The electron temperature T e and emission measure (EM) are found using a geometric mean emission measure method. The EM derived from the elements Fe, Si, S, and Al are compared in order to measure relative coronal-to-photospheric abundance enhancement factors. We also studied the ion temperature T i and the non-thermal velocity v nt using the line profiles. All these measurements are compared to polar coronal hole observations from the previous (1996-1997) solar minimum and to model predictions for relative abundances. There are many similarities in the physical properties of the polar coronal holes between the two minima at these low heights. We find that the electron density, T e, and T i are comparable in both minima. T e shows a comparable gradient with height. Both minima show a decreasing T i with increasing charge-to-mass ratio q/M. A previously observed upturn of T i for ions above q/M>0.25 was not found here. We also compared relative coronal-to-photospheric elemental abundance enhancement factors for a number of elements. These ratios were ~1 for both the low first ionization potential (FIP) elements Si and Al and the marginally high FIP element S relative to the low FIP element Fe, as is expected based on earlier observations and models for a polar coronal hole. These results are consistent with no FIP effect in a polar coronal hole

Molecular Cloud Chemistry and The Importance of Dielectronic Recombination

Dielectronic recombination (DR) of singly charged ions is a reaction pathway that is commonly neglected in chemical models of molecular clouds. In this study we include state-of-the-art DR data for He+, C+, N+, O+, Na+, and Mg+ in chemical models used to simulate dense molecular clouds, protostars, and diffuse molecular clouds. We also update the radiative recombination (RR) rate coefficients for H+, He+, C+, N+, O+, Na+, and Mg+ to the current state-of-the-art values. The new RR data have little effect on the models. However, the inclusion of DR results in significant differences in gas-grain models of dense, cold molecular clouds for the evolution of a number of surface and gas-phase species. We find differences of a factor of 2 in the abundance for 74 of the 655 species at times of 104-106 yr in this model when we include DR. Of these 74 species, 16 have at least a factor of 10 difference in abundance. We find the largest differences for species formed on the surface of dust grains. These differences are due primarily to the addition of C+ DR, which increases the neutral C abundance, thereby enhancing the accretion of C onto dust. These results may be important for the warm-up phase of molecular clouds when surface species are desorbed into the gas phase. We also note that no reliable state-of-the-art RR or DR data exist for Si+, P+, S+, Cl+, and Fe+. Modern calculations for these ions are needed to better constrain molecular cloud models