Ruolo dei glicosaminoglicani su struttura e funzione dei crimps nei tendini e nei legamenti

The biomechanical roles of both tendons and ligaments are fulfilled by extracellular matrix of these tissues. In particular, tension is mainly transmitted and resisted by fibrous proteins (collagen, elastin), whereas compressive load is absorbed by water-soluble glycosaminoglycans (GAGs). GAGs spanning the interfibrillar spaces and interacting with fibrils also seem to play a part in transmitting and resisting tensile stresses. Apart from different functional roles and collagen array, tendons and ligaments share the same basic structure showing periodic undulations of collagen fibers or crimps. Each crimp is composed of many knots of each single fibril or fibrillar crimps. Fibrillar and fiber crimps act as shock absorbers during the initial elongation of both tendons and ligaments and assist the elastic recoil of fibrils and fibers when the tensile stress is removed. The aim of this thesis was to evaluate whether GAGs directly affect the 3D microstructural integrity of fibrillar crimp and fiber crimps in both tendons and ligaments. Achilles tendons and medial collateral ligaments of the knee from eight female Sprague-Dawley rats (90 days old) were digested with chondroitinase ABC to remove GAGs and observed under a scanning electron microscope (SEM). In addition, isolated fibrils from these tissues obtained by mechanical homogenization were analyzed by a transmission electron microscope (TEM). Both samples digested with chondroitinase ABC or mechanically disrupted still showed crimps and fibrillar crimps comparable to tissues with a normal GAGs content. All fibrils in the fibrillar crimp region always twisted leftwards, thus changing their running plane, and then sharply bent, changing their course on a new plane. These data suggest that GAGs do not affect structural integrity or fibrillar crimps functions that seem mainly related to the local fibril leftward twisting and the alternating handedness of collagen from a molecular to a supramolecular level.

Investigation on the Navigation Anomaly of Pioneer 10 and 11 probes

The present work consists of the investigation of the navigation of Pioneer 10 and 11 probes becoming known as the “Pioneer Anomaly”: the trajectories followed by the spacecrafts did not match the ones retrieved with standard navigation software. Mismatching appeared as a linear drift in the Doppler data received by the spacecrafts, which has been ascribed to a constant sunward acceleration of about 8.5×10-10 m/s2. The study presented hereafter tries to find a convincing explanation to this discrepancy. The research is based on the analysis of Doppler tracking data through the ODP (Orbit Determination Program), developed by NASA/JPL. The method can be summarized as: seek for any kind of physics affecting the dynamics of the spacecraft or the propagation of radiometric data, which may have not been properly taken into account previously, and check whether or not these might rule out the anomaly. A major effort has been put to build a thermal model of the spacecrafts for predicting the force due to anisotropic thermal radiation, since this is a model not natively included in the ODP. Tracking data encompassing more than twenty years of Pioneer 10 interplanetary cruise, plus twelve years of Pioneer 11 have been analyzed in light of the results of the thermal model. Different strategies of orbit determination have been implemented, including single arc, multi arc and stochastic filters, and their performance compared. Orbital solutions have been obtained without the needing of any acceleration other than the thermal recoil one indicating it as the responsible for the observed linear drift in the Doppler residuals. As a further support to this we checked that inclusion of additional constant acceleration as does not improve the quality of orbital solutions. All the tests performed lead to the conclusion that no anomalous acceleration is acting on Pioneers spacecrafts.