901 research outputs found
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
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
Hemodynamics in a giant intracranial aneurysm characterized by in vitro 4D flow MRI
No full textThe attached file "giant_ane_velocity_pressure_public_release.tar.gz" contains the processed data for the associated paper.Experimental and computational data suggest that hemodynamics play a critical role in the development, growth, and rupture of cerebral aneurysms. The flow structure, especially in aneurysms with a large sac, is highly complex and three-dimensional. Therefore, volumetric and time-resolved measurements of the flow properties are crucial to fully characterize the hemodynamics. In this study, phase-contrast Magnetic Resonance Imaging is used to assess the fluid dynamics inside a 3D-printed replica of a giant intracranial aneurysm, whose hemodynamics was previously simulated by multiple research groups. The physiological inflow waveform is imposed in a flow circuit with realistic cardiovascular impedance. Measurements are acquired with sub-millimeter spatial resolution for 16 time steps over a cardiac cycle, allowing for the detailed reconstruction of the flow evolution. Moreover, the three-dimensional and time-resolved pressure distribution is calculated from the velocity field by integrating the fluid dynamics equations, and is validated against differential pressure measurements using precision transducers. The flow structure is characterized by vortical motions that persist within the aneurysm sac for most of the cardiac cycle. All the main flow statistics including velocity, vorticity, pressure, and wall shear stress suggest that the flow pattern is dictated by the aneurysm morphology and is largely independent of the pulsatility of the inflow, at least for the flow regimes investigated here. Comparisons are carried out with previous computational simulations that used the same geometry and inflow conditions, both in terms of cycle-averaged and systolic quantities.Winston and Maxine Wallin Neuroscience Discovery FundAmili, Omid; Schiavazzi, Daniele; Moen, Sean; Jagadeesan, Bharathi; Van de Moortele, Pierre-François; Coletti, Filippo. (2017). Hemodynamics in a giant intracranial aneurysm characterized by in vitro 4D flow MRI. Retrieved from the University Digital Conservancy, https://doi.org/10.13020/D6WX0S
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
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
d-Dimensional Kepler–Coulomb Sturmians and Hyperspherical Harmonics as Complete Orthonormal Atomic and Molecular Orbitals
No full textSturmian basis sets are increasingly finding applications to the description of atomic and molecular structure, because of their mathematical properties and their flexibility regarding the ability to describe features of specific physical problems. However, their nature and properties have not been fully exploited in quantum chemistry. In this work we present a classification of Kepler-Coulomb Sturmian sets, where notations, symmetry properties, useful formulae, and relationships are described in detail, so to provide support for their applications to physical problems. The mathematical solution of Schrodinger equation is given for these sets both in configuration and momentum space, where Sturmian eigenfunctions coincide with hyperspherical harmonics and connections between different sets manifestly appear as elements of angular momentum algebra. Applications of the considered sets and some of their generalizations are also briefly accounted for
Numerical simulation of the insert chemistry of the hollow cathode from the deep space 1 ion engine 30,000 Hrs life test
No full textA model for the insert chemistry developed by the authors and based on the knowledge of the BaO – CaO – Al2O3 ternary system the ELT discharge cathode insert from the Deep Space 1 life test has been simulated. The computed data show a good agreement with the experimental one; the agreement increase with the imposition of boundary conditions closer to the experimental evidence. Tungsten deposition effect have been introduced into the model using experimental data and further improving the agreement between computed and measured data. The deposition trend found suggests the possibility of a link between barium depletion and tungsten deposition
Quantum-classical calculation of cross sections and rate constants for the H2+CN→HCN+H reaction
No full text
Quantum dressed classical mechanics: application to chemical reactions
No full textReaction dynamics of a four atom system is investigated using a time-dependent Gauss-Hermite discrete variable representation (TDGH-DVR) method. The method is applied to the description of vibrational degrees of freedom in the calculation of initially state selected cross-sections for the reaction H-2 + CN --> HCN + H, while translational and rotational motions are treated classically
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