| 1. |
- Crary, John F., et al.
(författare)
-
Primary age-related tauopathy (PART) : a common pathology associated with human aging
- 2014
-
Ingår i: Acta Neuropathologica. - : Springer Science and Business Media LLC. - 0001-6322 .- 1432-0533. ; 128:6, s. 755-766
-
Tidskriftsartikel (refereegranskat)abstract
- We recommend a new term, "primary age-related tauopathy" (PART), to describe a pathology that is commonly observed in the brains of aged individuals. Many autopsy studies have reported brains with neurofibrillary tangles (NFTs) that are indistinguishable from those of Alzheimer's disease (AD), in the absence of amyloid (A beta) plaques. For these "NFT+/A beta-aEuroe brains, for which formal criteria for AD neuropathologic changes are not met, the NFTs are mostly restricted to structures in the medial temporal lobe, basal forebrain, brainstem, and olfactory areas (bulb and cortex). Symptoms in persons with PART usually range from normal to amnestic cognitive changes, with only a minority exhibiting profound impairment. Because cognitive impairment is often mild, existing clinicopathologic designations, such as "tangle-only dementia" and "tangle-predominant senile dementia", are imprecise and not appropriate for most subjects. PART is almost universally detectable at autopsy among elderly individuals, yet this pathological process cannot be specifically identified pre-mortem at the present time. Improved biomarkers and tau imaging may enable diagnosis of PART in clinical settings in the future. Indeed, recent studies have identified a common biomarker profile consisting of temporal lobe atrophy and tauopathy without evidence of A beta accumulation. For both researchers and clinicians, a revised nomenclature will raise awareness of this extremely common pathologic change while providing a conceptual foundation for future studies. Prior reports that have elucidated features of the pathologic entity we refer to as PART are discussed, and working neuropathological diagnostic criteria are proposed.
|
|
| 2. |
- Garnier, Philippe, et al.
(författare)
-
The influence of the secondary electrons induced by energetic electrons impacting the Cassini Langmuir probe at Saturn
- 2013
-
Ingår i: Journal of geophysical research Space Physics. - 2169-9402. ; 118:11, s. 7054-7073
-
Tidskriftsartikel (refereegranskat)abstract
- The Cassini Langmuir Probe (LP) onboard the Radio and Plasma Wave Science experiment has provided much information about the Saturnian cold plasma environment since the Saturn Orbit Insertion in 2004. A recent analysis revealed that the LP is also sensitive to the energetic electrons (250–450 eV) for negative potentials. These electrons impact the surface of the probe and generate a current of secondary electrons, inducing an energetic contribution to the DC level of the current-voltage (I-V) curve measured by the LP. In this paper, we further investigated this influence of the energetic electrons and (1) showed how the secondary electrons impact not only the DC level but also the slope of the (I-V) curve with unexpected positive values of the slope, (2) explained how the slope of the (I-V) curve can be used to identify where the influence of the energetic electrons is strong, (3) showed that this influence may be interpreted in terms of the critical and anticritical temperatures concept detailed by Lai and Tautz (2008), thus providing the first observational evidence for the existence of the anticritical temperature, (4) derived estimations of the maximum secondary yield value for the LP surface without using laboratory measurements, and (5) showed how to model the energetic contributions to the DC level and slope of the (I-V) curve via several methods (empirically and theoretically). This work will allow, for the whole Cassini mission, to clean the measurements influenced by such electrons. Furthermore, the understanding of this influence may be used for other missions using Langmuir probes, such as the future missions Jupiter Icy Moons Explorer at Jupiter, BepiColombo at Mercury, Rosetta at the comet Churyumov-Gerasimenko, and even the probes onboard spacecrafts in the Earth magnetosphere.
|
|
| 3. |
- Hill, T. W., et al.
(författare)
-
Charged nanograins in the Enceladus plume
- 2012
-
Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 117, s. A05209-
-
Tidskriftsartikel (refereegranskat)abstract
- There have been three Cassini encounters with the south-pole eruptive plume of Enceladus for which the Cassini Plasma Spectrometer (CAPS) had viewing in the spacecraft ram direction. In each case, CAPS detected a cold dense population of heavy charged particles having mass-to-charge (m/q) ratios up to the maximum detectable by CAPS (similar to 10(4) amu/e). These particles are interpreted as singly charged nanometer-sized water-ice grains. Although they are detected with both negative and positive net charges, the former greatly outnumber the latter, at least in the m/q range accessible to CAPS. On the most distant available encounter (E3, March 2008) we derive a net (negative) charge density of up to similar to 2600 e/cm(3) for nanograins, far exceeding the ambient plasma number density, but less than the net (positive) charge density inferred from the RPWS Langmuir probe data during the same plume encounter. Comparison of the CAPS data from the three available encounters is consistent with the idea that the nanograins leave the surface vents largely uncharged, but become increasingly negatively charged by plasma electron impact as they move farther from the satellite. These nanograins provide a potentially potent source of magnetospheric plasma and E-ring material.
|
|
| 4. |
- Ma, Y. J., et al.
(författare)
-
The importance of thermal electron heating in Titan's ionosphere : Comparison with Cassini T34 flyby
- 2011
-
Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 116, s. A10213-
-
Tidskriftsartikel (refereegranskat)abstract
- We use a new magnetohydrodynamic (MHD) model to study the effects of thermal-electron heating in Titan's ionosphere. This model improves the previously used multispecies MHD model by solving both the electron and ion pressure equations instead of a single plasma pressure equation. This improvement enables a more accurate evaluation of ion and electron temperatures inside Titan's ionosphere. The model is first applied to an idealized case, and the results are compared in detail with those of the single-pressure MHD model to illustrate the effects of the improvement. Simulation results show that the dayside ionosphere thermal pressure is larger than the upstream pressure during normal conditions, when Titan is located in the dusk region; thus Saturn's magnetic field is shielded by the highly conducting ionosphere, similar to the interaction of Venus during solar maximum conditions. This model is also applied to a special flyby of Titan, the T34 flyby, which occurred near the dusk region. It is shown that better agreement with the magnetometer data can be achieved using the two-fluid MHD model with the inclusion of the effects of thermal electron heating. The model results clearly demonstrate the importance of thermal-electron heating in Titan's ionosphere.
|
|
| 5. |
- Garnier, P., et al.
(författare)
-
The detection of energetic electrons with the Cassini Langmuir probe at Saturn
- 2012
-
Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 117, s. A10202-
-
Tidskriftsartikel (refereegranskat)abstract
- The Cassini Langmuir probe, part of the Radio and Plasma Wave Science (RPWS) instrument, has provided a wealth of information about the cold and dense plasma in the Saturnian system. The analysis of the ion side current (current for negative potentials) measured by the probe from 2005 to 2008 reveals also a strong sensitivity to energetic electrons (250-450 eV). These electrons impact the surface of the probe, and generate a detectable current of secondary electrons. A broad secondary electrons current region is inferred from the observations in the dipole L Shell range of similar to 6-10, with a peak full width at half maximum (FWHM) at L = 6.4-9.4 (near the Dione and Rhea magnetic dipole L Shell values). This magnetospheric flux tube region, which displays a large day/night asymmetry, is related to the similar structure in the energetic electron fluxes as the one measured by the onboard Electron Spectrometer (ELS) of the Cassini Plasma Spectrometer (CAPS). It corresponds spatially to both the outer electron radiation belt observed by the Magnetosphere Imaging Instrument (MIMI) at high energies and to the low-energy peak which has been observed since the Voyager era. Finally, a case study suggests that the mapping of the current measured by the Langmuir probe for negative potentials can allow to identify the plasmapause-like boundary recently identified at Saturn, and thus potentially identify the separation between the closed and open magnetic field lines regions.
|
|
| 6. |
- Richard, M. S., et al.
(författare)
-
Energetics of Titan's ionosphere : Model comparisons with Cassini data
- 2011
-
Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 116, s. A09310-
-
Tidskriftsartikel (refereegranskat)abstract
- Observed electron and ion temperatures in planetary ionospheres are higher than the neutral temperature. Instruments on board the Cassini spacecraft have shown this is also true for Titan. The Radio and Plasma Wave Science Langmuir Probe (RPWS-LP) (Wahlund et al., 2005) has measured electron temperatures above 1000 K. Ionospheric ion temperatures were deduced from a combined analysis of data from the Cassini Plasma Spectrometer and Ion and Neutral Mass Spectrometer (INMS) (Crary et al., 2009). Elevated electron temperatures attributed to heating by suprathermal electrons were predicted by pre-Cassini models (e.g., Gan et al., 1992; Roboz and Nagy, 1994) and observed by the Cassini electron spectrometer. Models of the energetic electrons and ions are presented that include Cassini inputs (i.e., measured neutral densities from INMS). The results are compared between 800 and 1800 km with suprathermal electron fluxes and plasma temperatures measured by Cassini instruments emphasizing the thermal electron temperature. Using only solar inputs, the dayside model agrees well with electron temperatures measured by RPWS-LP (Agren et al., 2009) between 1000 and 1400 km. At higher altitudes energy input from magnetospheric electrons is needed to reproduce the measured temperature. Incorporating typical magnetospheric electron fluxes into the dayside does not noticeably increase ion production near the ionospheric peak; however, effects can be seen near 1350 km. Joule heating effects are shown to be capable of contributing significantly to the ion temperature. Magnetospheric suprathermal electrons are shown to provide sufficient heating for the thermal electron population in the middle to upper ionosphere on the nightside.
|
|
| 7. |
- Sillanpaeae, I., et al.
(författare)
-
Cassini Plasma Spectrometer and hybrid model study on Titan's interaction : Effect of oxygen ions
- 2011
-
Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 116, s. A07223-
-
Tidskriftsartikel (refereegranskat)abstract
- During the Cassini Titan flyby on 2 July 2006 (T15), Titan was surrounded by a magnetospheric plasma flow with density about 0.1 cm(-3) as measured by Cassini Plasma Spectrometer (CAPS). A very low fraction of water group ions (O(+)) was detected in the flow dominated by hydrogen ions. We show that Titan's plasma interaction can be highly sensitive to the small fraction of oxygen ions in the magnetospheric flow. The ion quantities of the magnetospheric flow during the flyby were obtained from numerical moments calculated from the CAPS measurements; the average ambient magnetic field was determined using the Cassini magnetometer data. We simulated the flyby using a global hybrid model; the water group abundance in the flow was varied in three simulation runs. Based on the simulation results, the oxygen content has an especially notable effect on the extent of Titan's induced magnetosphere. A multi-instrument analysis was performed comparing with the simulations, whereby a comprehensive picture of the plasma properties around Titan during this flyby was obtained. Comparisons between the hybrid model simulations and Cassini measurements during the flyby point toward O+ density in the undisturbed magnetospheric flow having been around 0.008 cm(-3), which would have accounted for one half of the dynamic pressure of the flow.
|
|
