The Cassini cameras have captured the opposition effect in Saturn rings with a high radial resolution at phase angles down to 0.01o in the entire main ring system. We derive phase functions from 0.01 ...to 25 degrees of phase angle in the Wide-Angle Camera clear filters with a central wavelength of 0.611microns and phase functions from 0.001 to 25 degrees of phase angle in the Narrow-Angle and Wide-Angle Cameras color filters (from the blue 0.451 microns to the near infrared 0.752 microns). We characterize the morphology of the phase functions of different features in the main rings. We find that the shape of the phase function is accurately represented by a logarithmic model (Bobrov 1970, in Surfaces and Interiors of Planets and Satellites, Academic, edited by A. Dollfus). For practical purposes, we also parametrize the phase curves by a simple linear-by-part model (Lumme and Irvine 1976, Astronomical Journal, 81, p865), which provides three morphological parameters : the amplitude and the Half-Width at Half-Maximum (HWHM) of the surge, and the slope S of the linear-part of the phase function at larger phase angles. Our analysis demonstrates that all of these parameters show trends with the optical depth of the rings. These trends imply that the optical depth is a key-element determining the physical properties which act on the opposition effect. Wavelength variations of the morphological parameters of the surge show important trends with the optical depth in the green filter (0.568 microns), which implies that grain size effects are maximum in this wavelength.
The origin of Saturn's inner mid-sized moons (Mimas, Enceladus, Tethys, Dione and Rhea) and Saturn's rings is debated. Charnoz et al. (2010) introduced the idea that the smallest inner moons could ...form from the spreading of the rings' edge while Salmon et al. (2010) showed that the rings could have been initially massive, and so was the ring's progenitor itself. One may wonder if the mid-sized moons may have formed also from the debris of a massive ring progenitor, as also suggested in Canup (2010). However, the process driving mid-sized moons accretion from the icy debris disks has not been investigated in details. In particular, this process does not seem able to explain the varying silicate contents of the mid-sized moons (from 6% to 57% in mass). Here, we explore the formation of large objects from a massive ice-rich ring (a few times Rhea's mass) and describe the fundamental properties and implications of this new process. Using a hybrid computer model, we show that accretion within massive icy rings can form all mid-sized moons from Mimas to Rhea. However in order to explain their current locations, intense dissipation within Saturn (with Qp<2000) would be required. Our results are consistent with a satellite origin tied to the rings formation at least 2.5 Gy ago, both compatible with either a formation concurrent to Saturn or during the Late Heavy Bombardment. Tidal heating related to high-eccentricity post-accretional episodes may induce early geological activity. If some massive irregular chunks of silicates were initially present within the rings, they would be present today inside the satellites' cores which would have accreted icy shells while being tidally expelled from the rings (via a heterogeneous accretion process)while those still present in the rings are interpreted as today Saturn's rings' propellers and ring-moons (like Pan or Daphnis).
Computer-Assisted Digestive Surgery Soler, Luc; Nicolau, Stéphane; Hostettler, Alexandre ...
Computational Surgery and Dual Training
Book Chapter
Introducing an optical device into the abdomen of a patient so as to carry out the surgical procedure via a miniaturized camera represented the major change the surgical world experienced during the ...twentieth century: the “minimally invasive” surgery era was born. This revolution is about to experience a new twist linked to the appearance of a new original technique called Natural Orifice Transluminal Endoscopic Surgery (NOTES) that could replace traditional laparoscopic surgery for a large set of procedures. By replacing the rigid optic that is introduced through the skin by a flexible optic that is introduced through a natural orifice such as stomach, vagina or colon, this new technique should eliminate all visible incisions.
If the benefits for patients have clearly been proved for laparoscopic surgery, and whatever the result for NOTES, such minimally invasive techniques bring up new difficulties for surgeons, thus reducing their gesture capacity. The first difficulty is the loss of several senses such as the sense of touch and a modification of the force feedback feeling. In NOTES, this loss is greatly amplified due to the length of instruments making it difficult to feel a contact between an instrument and an organ. This lack of force feedback is also featured by current robotic systems, such as the Da Vinci robot from the Intuitive Surgical Company, currently the most used surgical robot worldwide. The use of stereoscopic vision, however, allowed to lessen that perception limit, compensating it by a 3D view of the operative scene filmed by two cameras. But this technique will be difficult to implement for transluminal endoscopic surgery, since it requires the extreme miniaturization of cameras while maintaining a high image resolution. Another solution consists in using virtual reality and augmented reality. Indeed, virtual reality allows to provide a preoperative 3D view of patients, operated from their medical image (CT scan or MRI). This virtual copy of patients can then be used in a preoperative simulator, what provides a realistic 3D view of patients.
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