74 research outputs found
An empirical approach to modeling ion production rates in Titan's ionosphere II: Ion production rates on the nightside
Ionization of neutrals by precipitating electrons and ions is the main source of Titan's nightside ionosphere. This paper has two goals: (1) characterization of the role of electron impact ionization on the nightside ionosphere for different magnetospheric conditions and (2) presentation of empirical ion production rates determined using densities measured by the Cassini Ion and Neutral Mass Spectrometer on the nightside. The ionosphere between 1000 and 1400 km is emphasized. We adopt electron fluxes measured by the Cassini Plasma Spectrometer-Electron Spectrometer and the Magnetospheric Imaging Instrument as classified by Rymer et al. (2009). The current paper follows an earlier paper (Paper I), in which we investigated sources of Titan's dayside ionosphere and demonstrated that the photoionization process is well understood. The current paper (Paper II) demonstrates that modeled and empirical ionization rates on the nightside are in agreement with an electron precipitation source above 1100 km. Ion production rate profiles appropriate for different Saturnian magnetospheric conditions, as outlined by Rymer et al., are constructed for various magnetic field topologies. Empirical production rate profiles are generated for deep nightside flybys of Titan. The results also suggest that at lower altitudes (below 1100 km) another source, such as ion precipitation, is probably needed
An empirical approach to modeling ion production rates in Titan’s ionosphere I: Ion production rates on the dayside and globally
Titan's ionosphere is created when solar photons, energetic magnetospheric electrons or ions, and cosmic rays ionize the neutral atmosphere. Electron densities generated by current theoretical models are much larger than densities measured by instruments on board the Cassini orbiter. This model density overabundance must result either from overproduction or from insufficient loss of ions. This is the first of two papers that examines ion production rates in Titan's ionosphere, for the dayside and nightside ionosphere, respectively. The first (current) paper focuses on dayside ion production rates which are computed using solar ionization sources (photoionization and electron impact ionization by photoelectrons) between 1000 and 1400 km. In addition to theoretical ion production rates, empirical ion production rates are derived from CH4, CH3+, and CH4+ densities measured by the INMS (Ion Neutral Mass Spectrometer) for many Titan passes. The modeled and empirical production rate profiles from measured densities of N2+ and CH4+ are found to be in good agreement (to within 20%) for solar zenith angles between 15 and 90°. This suggests that the overabundance of electrons in theoretical models of Titan's dayside ionosphere is not due to overproduction but to insufficient ion losses
Nonlinear measure of synchrony between blood oxygen saturation and heart rate from nocturnal pulse oximetry in obstructive sleep apnoea syndrome
Recommended from our members
Effect of lung volume and intrathoracic pressure on airway mucosal blood flow in man
We have recently described an inert soluble gas uptake technique (using dimethyl-ether, DME) for the non-invasive measurement of airway mucosal blood flow (Qaw) in humans. In the present study, we assessed the effects of lung volume and intrathoracic pressure on Qaw, in healthy non-smokers (age range 19-52 years). Qaw was calculated from the steady-state uptake of DME from a 50 ml segment of the anatomic dead space. The mean (+/- SD) Qaw of three consecutive measurements at a lung volume of FRC + 300 ml was 8.3 +/- 2.3, 8.6 +/- 2.6 and 8.3 +/- 2.7 ml.min-1 (n = 13; coefficient of variation 14 +/- 7%). At zero airway pressure, there was an inverse relationship between apparent Qaw on the one hand and lung volume and anatomic dead space (DS) on the other: mean Qaw was 12.2 +/- 5.3, 8.2 +/- 2.5 and 5.3 +/- 2.2 ml.min-1 at RV + 300 ml (DS = 131 +/- 11 ml), FRC + 300 ml (DS = 153 +/- 12 ml) and TLC (DS = 206 +/- 22 ml) positions, respectively (n = 11; P < 0.05 among all three). At a lung volume of FRC + 300 ml, an increase in intrathoracic pressure to +25 cmH2O (modified Valsalva maneuver) decreased mean Qaw to 3.3 +/- 2.8 ml.min-1 while a decrease in intrathoracic pressure to -35 cmH2O (modified Müller maneuver) increased mean Qaw to 17.1 +/- 7.4 ml.min-1 from a control value of 7.2 +/- 2.2 ml.min-1 (n = 7; P < 0.05 among all three). These results indicate that lung volume has an effect on apparent Qaw, presumably by influencing the depth to which the analyzed anatomical dead space segment extends into the bronchial tree. The results also show that changes in intrathoracic pressure alter Qaw, possibly reflecting concomitant changes in left ventricular output and its distribution to intrathoracic and extrathoracic vascular beds
Recommended from our members
Airway mucosal blood flow: response to autonomic and inflammatory stimuli
A major portion of airway blood flow is distributed to the subepithelial tissue space and is strategically located to influence both epithelial and airway smooth muscle functions. To assess the magnitude and responsiveness of blood flow through the subepithelial microvasculature, we measured tracheal mucosal blood flow with a soluble gas method in intact sheep. We found responses of tracheal mucosal blood flow to pharmacological stimuli alpha- and beta- (adrenoceptor agonists) and inflammatory stimuli (antigen and histamine), and demonstrated that alterations in mucosal blood flow influence the magnitude and duration of allergic airway smooth muscle contraction in the trachea. Mucosal blood flow, which under certain circumstances is regulated independently of total airway blood flow, could play a critical role in the manifestations of and recovery from airway disease
Hyperekplexia: Report of a Nonfamilial Adult Onset Case Associated With Obstructive Sleep Apnea and Abnormal Brain Nuclear Tomography
- …