| 1. |
- Cravens, T. E., et al.
(författare)
-
Dynamical and magnetic field time constants for Titan's ionosphere : Empirical estimates and comparisons with Venus
- 2010
-
Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 115:8, s. A08319-
-
Tidskriftsartikel (refereegranskat)abstract
- Plasma in Titan's ionosphere flows in response to forcing from thermal pressure gradients, magnetic forces, gravity, and ion-neutral collisions. This paper takes an empirical approach to the ionospheric dynamics by using data from Cassini instruments to estimate pressures, flow speeds, and time constants on the dayside and nightside. The plasma flow speed relative to the neutral gas speed is approximately 1 m s(-1) near an altitude of 1000 km and 200 m s(-1) at 1500 km. For comparison, the thermospheric neutral wind speed is about 100 m s(-1). The ionospheric plasma is strongly coupled to the neutrals below an altitude of about 1300 km. Transport, vertical or horizontal, becomes more important than chemistry in controlling ionospheric densities above about 1200-1500 km, depending on the ion species. Empirical estimates are used to demonstrate that the structure of the ionospheric magnetic field is determined by plasma transport (including neutral wind effects) for altitudes above about 1000 km and by magnetic diffusion at lower altitudes. The paper suggests that a velocity shear layer near 1300 km could exist at some locations and could affect the structure of the magnetic field. Both Hall and polarization electric field terms in the magnetic induction equation are shown to be locally important in controlling the structure of Titan's ionospheric magnetic field. Comparisons are made between the ionospheric dynamics at Titan and at Venus.
|
|
| 2. |
- Aidas, Kestutis, et al.
(författare)
-
The Dalton quantum chemistry program system
- 2014
-
Ingår i: Wiley Interdisciplinary Reviews. Computational Molecular Science. - : Wiley. - 1759-0876. ; 4:3, s. 269-284
-
Tidskriftsartikel (refereegranskat)abstract
- Dalton is a powerful general-purpose program system for the study of molecular electronic structure at the Hartree-Fock, Kohn-Sham, multiconfigurational self-consistent-field, MOller-Plesset, configuration-interaction, and coupled-cluster levels of theory. Apart from the total energy, a wide variety of molecular properties may be calculated using these electronic-structure models. Molecular gradients and Hessians are available for geometry optimizations, molecular dynamics, and vibrational studies, whereas magnetic resonance and optical activity can be studied in a gauge-origin-invariant manner. Frequency-dependent molecular properties can be calculated using linear, quadratic, and cubic response theory. A large number of singlet and triplet perturbation operators are available for the study of one-, two-, and three-photon processes. Environmental effects may be included using various dielectric-medium and quantum-mechanics/molecular-mechanics models. Large molecules may be studied using linear-scaling and massively parallel algorithms. Dalton is distributed at no cost from for a number of UNIX platforms.
|
|
| 3. |
- Jonkman, Nini H., et al.
(författare)
-
Do self-management interventions work in patients with heart failure? An individual patient data meta-analysis
- 2016
-
Ingår i: Circulation. - : Lippincott Williams & Wilkins. - 0009-7322 .- 1524-4539. ; 133:12, s. 1189-1198
-
Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: -Self-management interventions are widely implemented in care for patients with heart failure (HF). Trials however show inconsistent results and whether specific patient groups respond differently is unknown. This individual patient data meta-analysis assessed the effectiveness of self-management interventions in HF patients and whether subgroups of patients respond differently.METHODS AND RESULTS: -Systematic literature search identified randomized trials of self-management interventions. Data of twenty studies, representing 5624 patients, were included and analyzed using mixed effects models and Cox proportional-hazard models including interaction terms. Self-management interventions reduced risk of time to the combined endpoint HF-related hospitalization or all-cause death (hazard ratio [HR], 0.80; 95% confidence interval [CI], 0.71-0.89), time to HF-related hospitalization (HR, 0.80; 95%CI, 0.69-0.92), and improved 12-month HF-related quality of life (standardized mean difference 0.15; 95%CI, 0.00-0.30). Subgroup analysis revealed a protective effect of self-management on number of HF-related hospital days in patients <65 years (mean number of days 0.70 days vs. 5.35 days; interaction p=0.03). Patients without depression did not show an effect of self-management on survival (HR for all-cause mortality, 0.86; 95%CI, 0.69-1.06), while in patients with moderate/severe depression self-management reduced survival (HR, 1.39; 95%CI, 1.06-1.83, interaction p=0.01).CONCLUSIONS: -This study shows that self-management interventions had a beneficial effect on time to HF-related hospitalization or all-cause death, HF-related hospitalization alone, and elicited a small increase in HF-related quality of life. The findings do not endorse limiting self-management interventions to subgroups of HF patients, but increased mortality in depressed patients warrants caution in applying self-management strategies in these patients.
|
|
| 4. |
- Luhmann, J. G., et al.
(författare)
-
Investigating magnetospheric interaction effects on Titan's ionosphere with the Cassini orbiter Ion Neutral Mass Spectrometer, Langmuir Probe and magnetometer observations during targeted flybys
- 2012
-
Ingår i: Icarus. - : Elsevier BV. - 0019-1035 .- 1090-2643. ; 219:2, s. 534-555
-
Tidskriftsartikel (refereegranskat)abstract
- In the similar to 6 years since the Cassini spacecraft went into orbit around Saturn in 2004, roughly a dozen Titan flybys have occurred for which the Ion Neutral Mass Spectrometer (INMS) measured that moon's ionospheric density and composition. For these, and for the majority of the similar to 60 close flybys probing to altitudes down to similar to 950 km, Langmuir Probe electron densities were also obtained. These were all complemented by Cassini magnetometer observations of the magnetic fields affected by the Titan plasma interaction. Titan's ionosphere was expected to differ from those of other unmagnetized planetary bodies because of significant contributions from particle impact due to its magnetospheric environment. However, previous analyses of these data clearly showed the dominance of the solar photon source, with the possible exception of the nightside. This paper describes the collected ionospheric data obtained in the period between Cassini's Saturn Orbit Insertion in 2004 and 2009, and examines some of their basic characteristics with the goal of searching for magnetospheric influences. These influences might include effects on the altitude profiles of impact ionization by magnetospheric particles at the Titan orbit location, or by locally produced pickup ions freshly created in Titan's upper atmosphere. The effects of forces on the ionosphere associated with both the draped and penetrating external magnetic fields might also be discernable. A number of challenges arise in such investigations given both the observed order of magnitude variations in the magnetospheric particle sources and the unsteadiness of the magnetospheric magnetic field and plasma flows at Titan's (similar to 20Rs (Saturn Radius)) orbit. Transterminator flow of ionospheric plasma from the dayside may also supply some of the nightside ionosphere, complicating determination of the magnetospheric contribution. Moreover, we are limited by the sparse sampling of the ionosphere during the mission as the Titan interaction also depends on Saturn Local Time as well as possible intrinsic asymmetries and variations of Titan's neutral atmosphere. We use organizations of the data by key coordinate systems of the plasma interaction with Titan's ionosphere to help interpret the observations. The present analysis does not find clear characteristics of the magnetosphere's role in defining Titan's ionosphere. The observations confirm the presence of an ionosphere produced mainly by sunlight, and an absence of expected ionospheric field signatures in the data. Further investigation of the latter, in particular, may benefit from numerical experiments on the inner boundary conditions of 3D models including the plasma interaction and features such as neutral winds.
|
|
| 5. |
- Ulusen, D., et al.
(författare)
-
Comparisons of Cassini flybys of the Titan magnetospheric interaction with an MHD model : Evidence for organized behavior at high altitudes
- 2012
-
Ingår i: Icarus. - : Elsevier BV. - 0019-1035 .- 1090-2643. ; 217:1, s. 43-54
-
Tidskriftsartikel (refereegranskat)abstract
- Recent papers suggest the significant variability of conditions in Saturn's magnetosphere at the orbit of Titan. Because of this variability, it was expected that models would generally have a difficult time regularly comparing to data from the Titan flybys. However, we find that in contrast to this expectation, it appears that there is underlying organization of the interaction features roughly above similar to 1800 km (1.7 Rt) altitude by the average external field due to Saturn's dipole moment. In this study, we analyze Cassini's plasma and magnetic field data collected at 9 Titan encounters during which the external field is close to the ideal southward direction and compare these observations to the results from a 2-fluid (1 ion, 1 electron) 7-species MHD model simulations obtained under noon SLT conditions. Our comparative analysis shows that under noon SLT conditions the Titan plasma interaction can be viewed in two layers: an outer layer between 6400 and 1800 km where interaction features observed in the magnetic field are in basic agreement with a purely southward external field interaction and an inner layer below 1800 km where the magnetic field measurements show strong variations and deviate from the model predictions. Thus the basic features inferred from the Voyager 1 flyby seem to be generally present above similar to 1800 km in spite of the ongoing external variations from SLT excursions, time variability and magnetospheric current systems as long as a significant southward external field component is present. At around similar to 1800 km kinetic effects (such as mass loading and heavy ion pickup) and below 1800 km ionospheric effects (such as drag of ionospheric plasma due to coupling with neutral winds and/or magnetic memory of Titan's ionosphere) complicate what is observed.
|
|
| 6. |
- Wahlund, Jan Erik, et al.
(författare)
-
On the amount of heavy molecular ions in Titan's ionosphere
- 2009
-
Ingår i: Planetary and Space Science. - : Elsevier BV. - 0032-0633 .- 1873-5088. ; 57:14-15, s. 1857-1865
-
Tidskriftsartikel (refereegranskat)abstract
- We present observational evidence that the ionosphere of Titan below an altitude of 1150 km is a significant source of heavy (> 100 amu) molecular organic species. This study is based on measurements by five instruments (RPWS/LP, RPWS/E, INMS, CAPS/ELS, CAPS/IBS) onboard the Cassini spacecraft during three flybys (T17, T18, T32) of Titan. The ionospheric peaks encountered at altitudes of 950-1300 km had densities in the range 900-3000 cm(-3). Below these peaks the number densities of heavy positively charged ions reached 100-2000 cm(-3) and approached 50-70% of the total ionospheric density with an increasing trend toward lowest measured altitudes. Simultaneously measured negatively charged ion densities were in the range 50-150 cm(-3). These results imply that similar to 10(5)similar to 10(6) heavy positively charged ions/m(3)/s are continuously recombining into heavy neutrals and supply the atmosphere of Titan. The ionosphere may in this way produce 0.1-1 Mt/yr of heavy organic compounds and is therefore a sizable source for aerosol formation. We also predict that Titan's ionosphere is dominated by heavy (> 100 amu) molecular ions below 950 km.
|
|
| 7. |
- Edberg, Niklas J. T., et al.
(författare)
-
Extreme densities in Titan's ionosphere during the T85 magnetosheath encounter
- 2013
-
Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 40:12, s. 2879-2883
-
Tidskriftsartikel (refereegranskat)abstract
- We present Cassini Langmuir probe measurements of the highest electron number densities ever reported from the ionosphere of Titan. The measured density reached 4310cm(-3) during the T85 Titan flyby. This is at least 500cm(-3) higher than ever observed before and at least 50% above the average density for similar solar zenith angles. The peak of the ionospheric density is not reached on this flyby, making the maximum measured density a lower limit. During this flyby, we also report that an impacting coronal mass ejection (CME) leaves Titan in the magnetosheath of Saturn, where it is exposed to shocked solar wind plasma for at least 2 h 45 min. We suggest that the solar wind plasma in the magnetosheath during the CME conditions significantly modifies Titan's ionosphere by an addition of particle impact ionization by precipitating protons.
|
|
| 8. |
- Edberg, Niklas J. T., et al.
(författare)
-
Solar cycle modulation of Titan's ionosphere
- 2013
-
Ingår i: Journal of Geophysical Research-Space Physics. - : American Geophysical Union (AGU). - 2169-9380. ; 118:8, s. 5255-5264
-
Tidskriftsartikel (refereegranskat)abstract
- During the six Cassini Titan flybys T83-T88 (May 2012 to November 2012) the electron density in the ionospheric peak region, as measured by the radio and plasma wave science instrument/Langmuir probe, has increased significantly, by 15-30%, compared to previous average. These measurements suggest that a longterm change has occurred in the ionosphere of Titan, likely caused by the rise to the new solar maximum with increased EUV fluxes. We compare measurements from TA, TB, and T5, from the declining phase of solar cycle 23 to the recent T83-T88 measurements during cycle 24, since the solar irradiances from those two intervals are comparable. The peak electron densities normalized to a common solar zenith angle N-norm from those two groups of flybys are comparable but increased compared to the solar minimum flybys (T16-T71). The integrated solar irradiance over the wavelengths 1-80nm, i.e., the solar energy flux, F-e, correlates well with the observed ionospheric peak density values. Chapman layer theory predicts that NnormFek, with k=0.5. We find observationally that the exponent k=0.540.18. Hence, the observations are in good agreement with theory despite the fact that many assumptions in Chapman theory are violated. This is also in good agreement with a similar study by Girazian and Withers (2013) on the ionosphere of Mars. We use this power law to estimate the peak electron density at the subsolar point of Titan during solar maximum conditions and find it to be about 6500cm(-3), i.e., 85-160% more than has been measured during the entire Cassini mission.
|
|
| 9. |
- Edberg, Niklas J. T., et al.
(författare)
-
Structured ionospheric outflow during the Cassini T55-T59 Titan flybys
- 2011
-
Ingår i: Planetary and Space Science. - : Elsevier BV. - 0032-0633 .- 1873-5088. ; 59:8, s. 788-797
-
Tidskriftsartikel (refereegranskat)abstract
- During the final three of the five consecutive and similar Cassini Titan flybys T55-T59 we observe a region characterized by high plasma densities (electron densities of 1-8 cm(-3)) in the tail/nightside of Titan. This region is observed progressively farther downtail from pass to pass and is interpreted as a plume of ionospheric plasma escaping Titan, which appears steady in both location and time. The ions in this plasma plume are moving in the direction away from Titan and are a mixture of both light and heavy ions with composition revealing that their origin are in Titan's ionosphere, while the electrons are more isotropically distributed. Magnetic field measurements indicate the presence of a current sheet at the inner edge of this region. We discuss the mechanisms behind this outflow, and suggest that it could be caused by ambipolar diffusion, magnetic moment pumping or dispersive Alfven waves.
|
|
| 10. |
|
|
