197,438 research outputs found
Santuari d'Italia - Umbria
No full textCensimento e schedatura dei principali luoghi di culto di carattere santuariale esistenti in Umbria, con alcuni saggi introduttivi (saggi di M. Tosti, L. Pellegrini, C. Coletti, M.L. Proietti, F. Troiani
Hollow cathode life-time prediction from low work function surface coverage evolution
No full textIn this paper a procedure to update the plasma parameters relatively to changes of the hollow cathode surface work function has been developed. This procedure has been validated with experimental results and then coupled with the deposition/desorption model already developed by the authors. The evolution of the surface of the cathode tested for 28,000 hours by Sarver-Verhey has been simulated and from the data obtained an end of life criterion has been developed. Then using this criterion the ELT NSTAR discharge cathode has been simulated for various throttle conditions deriving the lifetime at TH0 (200,000 h), TH8 (100,000 h) and TH15 (25,000 h). The lifetimes found are in agreement with the theoretical expectation. The lifetime of the ELT NSTAR cathode under the throttling conditions used during the Deep Space 1 Spare Ion Engine life test has been found to be in excess of 30,000 hours and in particular 100,000 or more if the cathode is run at TH8 or lower from 30,000 hours onward
Hollow cathode chemical modelling
No full textIn this paper the state of hollow cathode life time modelling at the University of Southampton will be reported. Two models have been developed: one for BaO depletion from the hollow cathode insert and another for low work function compounds deposition and desorption. The model developed to predict BaO depletion from hollow cathode insert will be presented together with some comparison between experimental and numerical data to prove its validity.A model for low work function compounds deposition and desorption will also be presented. This model will be used to simulate the NSTAR cathode showing a very conservative estimate of the cathode life due to conservative character of the hypotheses made in the model development and due to the chosen criteria for the end of life
A chemical model for barium oxide depletion from hollow cathode’s insert
No full textIn this paper a chemical model to predict barium oxide depletion from hollow cathode insert is developed. This model is based on the knowledge of the ternary diagram that exists in the BaO-CaO-Al2O3 system. This model takes also into account the diffusive motion of barium oxide inside the insert. A comparison between numerical and experimental data is made to determine the diffusion coefficient inside the insert. The diffusion coefficient presents an Arrhenius trend with activation energy similar to the one of barium oxide evaporation. A two dimensional model is used to demonstrate how temperature profile along the insert is a key parameter to calculate barium depletion
Molecular signaling homology across muscle wasting conditions
No full textkeletal muscle tissue is remarkably simple as to its cell types, in comparison to other tissues: it is constituted by a terminally differentiated, gigantic syncytial cell type (the myofiber) and a quiescent, mononucleated stem cell (the satellite cell, SC). The latter grants regeneration and homeostasis following damage or atrophy, with the possible intervention of additional myogenic stem cells from the endomysium. In case of damage, the muscle fiber «is too big to fail» and survival is guaranteed by involving new resources, in the form of additional nuclei coming from the SC. Furthermore, the myofiber has a striking adaptative capacity to cope with the variable demand in contractile activity and mechanical load, by modulating the bulk protein reserve and the number and function of sarcomeres.
Based on the aforementioned characteristics of the system - a tissue with two components, having dicotomial responses such as fiber atrophy/hypertrophy or SC proliferation/differentiation - it is plausible to imagine that muscle adaptative responses are always the same, regardless of the stimulus. In other words, one would expect molecular signaling homology across muscle wasting conditions independently of the primary cause of wasting. In this perspective, for instance one could consider cachexia as an accelerated muscle wasting condition which differs from sarcopenia simply for its kinetics and severity. This way of reasoning has very relevant implications for funding agencies, researchers and physicians and, ultimately, the general population: for instance, common mechanisms would imply that findings related to muscle wasting associated to one disease would have fallouts for other disease-related muscle wasting conditions.
It is therefore of pivotal importance to discuss to which extent and how muscle wasting conditions differ from each other and which are, if any, the major regulatory factors involved. We will present some examples of such a homology, with emphasis on the crosstalk between: p53/Growth Factors, NF-kappaB/Serum Response Factor, and Pax7/Muscle Regulatory Factors.
References
Coletti D, Daou N, Hassani M, Li Z, Parlakian A. Serum Response Factor in muscle tissues: from development to ageing. Eur J Transl Myol. 2016; 26(2):6008
Coletti D, Teodori L, Li Z, Bernaudin JF, Adamo S. Restoration versus reconstruction: cellular mechanisms of skin, nerve and muscle regeneration compared. Regen Med Res, 1:4, 2013
Drescher C, Konishi M, Ebner N, Springer J. Loss of muscle mass: current developments in cachexia and sarcopenia focused on biomarkers and treatment. J Cachexia Sarcopenia Muscle. 2015 Dec;6(4):303-11
Magini (Magini Coletti) Antonio
No full textVoce enciclopedica sul cantante Antonio Magini Coletti (1855-1912
A dual Stage ion engine for high impulse missions
No full textIn this paper, the applicability of dual stage ion optics and in particular of the so-called dual stage ion engine to high power, high specific impulse missions will be evaluated. First, the performance limits of conventional two gridded ion engines (GIE) will be discussed and the advantages provided by dual stage ion engines reported. The limits of applicability of a dual stage ion engine will be analyzed analytically and the results confirmed numerically. The lifetime and performance of a three gridded dual stage ion engine (DS3G) will be numerically investigated and compared to those of a conventional GIE assessing for the first time in the open literature under what condition dual stage ion optics provide performance improvements over conventional GIEs and what is its impact on the thruster lifetime. Dual stage ion engines have been found to be capable of providing higher thrust density and longer lifetime with respect to conventional gridded ion engines
Solid state MPD thruster with applied magnetic field
No full textA solid state MPD thruster with applied magnetic field has been investigated. The MPDhas been operated with applied fields up to 0.4 T. Current, impulse bit and ablated masshave been measured. The thruster has shown a threshold value of the applied magnetic fieldover which it does not work, this threshold value increases with the shot energy. Away fromthis threshold value the current shows small variation with the applied field. The measuredvalues of the impulse bit are in accordance with the trends shown by previous investigationsand show a satisfactory agreement with the theoretical values calculated with one of theauthors’ theory
Le terre degli Italici
No full textI popoli italici dell’Appennino Centrale e dell’area medio-adriatica - Il popolamento italico nel territorio montano a Nord e a Sud della Salaria - La viabilità transappenninica: l’eredità della transumanza - Riferimenti bibliografic
Hollow cathode life time modelling
No full textHollow Cathodes (HCs) are of primary importance in the field of electric space propulsion, being used as electron sources in ion and Hall-effect thrusters. Hence, their lifetime is a key factor in all these applications.HCs have demonstrated the capability of providing up to 30,000 hours of operation, whereas no direct experimental data exist above this limit.The importance of HC lifetime is a growing issue for deep space missions usingpropulsive systems based on ion or Hall-effect thrusters that may require longerlifetimes than those demonstrated up to now. To address these concerns about HCs andto prove the suitability of an ion thrusters based solar electric propulsion subsystem forfuture high-impulse missions (such as Bepi Colombo), a model able to predict the HClifetime is needed.The model that has been developed in this thesis consists of three parts: a barium oxidedepletion model, a low work function surface coverage model and a plasma updateprocedure to calculate the effects that a change in the insert surface work function willproduce on the cathode plasma.The barium-oxide depletion model has been validated by comparing its results withexperimental measurements performed at QinetiQ and NASA, showing a goodquantitative agreement.The low-work function surface coverage model is the first of its kind to include theeffect of ion bombardment. The plasma update procedure, even if semi-empirical, isable to produce results that are in good agreement with the measurements.Using these three models the lifetime of the NSTAR hollow cathode has beensimulated, yielding predictions that are in good agreement with the theoreticalexpectations
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