7,107 research outputs found
Low-Thrust Earth-Venus Trajectories
No full textChapter 6, by Alessandro A. Quarta, Giovanni Mengali and Generoso Aliasi, discusses the simulation results involving the minimum-time trajectories for an Earth-Venus mission transfer using a spacecraft with an electric propulsion system, with both a nuclear and a solar electric power source. The analysis has been performed in a parametric way as a function of some design parameters, such as the available thruster electric power and the initial in-flight mass. Various models have been considered to describe the propulsion system behavior with different levels of
approximations and obtain increasingly refined information about the mission performance. Some simplifying assumptions have been introduced in order to make the mathematical problem tractable, to reduce the simulation time and guarantee a thorough parametric investigation of the mission performance. The analysis performed in this chapter is useful to obtain a first order estimate of the mission requirements as a function of the specific thruster characteristics
Filosofi italiani del Novecento e Cultura europea
No full textQuesto volume dal titolo Filosofi italiani del Novecento e Cultura europea raccoglie alcuni dei lavori che Antonio Quarta, Professore Associato di Storia della filosofia contemporanea e di Storia del- la Filosofia Italiana del Corso di Laurea in Filosofia dell’Università del Salento, ha prodotto in un arco di tempo che abbraccia più di quaranta anni di ininterrotta attività intellettuale. I quindici saggi che lo compongono mettono in rilievo la vastità degli interessi del loro autore, che spaziano dallo studio del fenomeno del tarantismo, all’analisi storica del processo di costruzione dell’identità culturale dell’Italia postunitaria. Ma il nucleo centrale di questa raccolta è costituito dagli studi e dalle ricerche che Antonio Quarta ha dedicato alla Storia della filosofia italiana dell’Ot- to e del Novecento, un tema che egli sviluppa puntualmente, con lucidità e rara chiarezza espositiva, in saggi dedicati ad alcune del- le maggiori figure intellettuali della filosofia italiana dei due se- coli appena trascorsi: da Carlo Cattaneo a Salvatore Trinchese, da Giovanni Vailati ad Eugenio Colorni, da Remo Cantoni a Giulio Preti, da Ludovico Geymonat a Ferruccio Rossi-Landi, da Benedetto Croce a Nicola Abbagnano, cui Quarta dedica un particolare interesse.
Ogni contributo restituisce a ciascun pensatore la sua dimensione sovranazionale e mette in evidenza la circolarità della filosofia italiana con quella della storia culturale europea, valorizzando così il ruolo del pensiero italiano nel contesto del dibattito internazionale
Special Orbits for Mercury Observation
No full textChapter 5, by Generoso Aliasi, Giovanni Mengali and Alessandro A. Quarta, deals with an advanced scientific mission concept in which the existence of suitable positions for the observation and the measurement of the Mercury’s magnetotail are investigated. The scientific mission is based on the use of artificial equilibrium points in the elliptic three-body system, constituted by the Sun, Mercury, and a spacecraft, which is modeled as a massless point. The spacecraft motion in the Sun–Mercury system is first discussed under the assumption that the propulsion
system provides a radial continuous thrust with respect to the Sun. In particular, the spacecraft is assumed to have a generalized sail as its primary propulsion system. A generalized sail models the performance of different types of advanced propulsion systems, including a (photonic) solar sail, an electric solar wind sail and an electric thruster, by simply modifying the value of a thrusting parameter. The location of the artificial equilibrium points is derived, and their stability is also investigated. It is shown that that collinear artificial equilibrium points are always
unstable, except for a range of L2-type points which are placed far away from Mercury. A similar result is obtained for triangular equilibrium points. A control strategy is introduced to maintain the spacecraft in the neighborhood of an artificial equilibrium point. In this context, a simple and effective way to actively control the spacecraft dynamics is by means of a Proportional-Integral-Derivative feedback control law. The latter control law is finally employed in the magnetotail mission scenario, whose fundamental idea is to continuously and slowly displacing the
artificial equilibrium point along the Sun–Mercury direction. Numerical simulations show the effectiveness of the proposed mission strategy
Optimal Solar Sail Phasing Trajectories for Circular Orbit
No full textThe concept of using a solar sail for the repositioning maneuver of a spacecraft on a heliocentric orbit was first proposed by McInnes [1]. In particular, assuming a circular orbit and a linearized dynamics model, Ref. [1] discusses the performance of a small (ideal) solar sail, subjected to a piecewise constant steering law, and compares its effectiveness with a situation in which a chemical (high-thrust) propulsion system is employed to perform the same maneuver. Subsequently, the study was extended by Mengali and Quarta [2], who solved the problem within an optimal framework, generalizing it to an elliptic orbit, a solar sail with an optical force model, and a scenario in which two spacecraft are simultaneously repositioned along the same starting orbit. The analysis of Ref. [2] was conducted using a nonlinear dynamics model for the solar sail’s heliocentric motion, which is, of course, fully general, but whose results can only be managed through numerical simulations. The aim of this Note is to show that, under the assumption of a linearized mathematical model [1], the optimal repositioning problem of an ideal, low-performance, solar sail can be solved within a semi-analytical framework. In particular, starting from a circular parking orbit, it is shown that the truly optimal steering law may be recovered in closed form
H2-Reversal Trajectory: a New Mission Application for High-Performance Solar Sails
No full textThe aim of this paper is to quantify the performance of a flat solar sail to perform a double angular momentum
reversal manoeuver and produce a new class of two-dimensional non-Keplerian orbits. The problem is
addressed in an optimal formulation and using a parametric approach. Two main difficulties must be properly
taken into account. On one side the sail must perform a rapid reorientation maneuver when it approaches
the Sun. It is shown by simulation that this assumption is reasonable. In second place the corresponding
trajectories require high performance solar sails, that is, sails with a characteristic acceleration greater than
3mm=s2. Such a value, although well beyond the currently available sail performance, is comparable (or
even lower) to that required by the original H-reversal maneuvers
CORRELAZIONE GENOTIPO-FENOTIPO NELLA CARDIOMIOPATIA ARITMOGENA DEL VENTRICOLO DESTRO
No full textABSTRACT 1 Background. With recognition of disease-causing genes in arrhythmogenic right ventricular cardiomyopathy, mutation
analysis is being applied.
Methods and Results. The role of genotyping in familial assessment for arrhythmogenic right ventricular cardiomyopathy
was investigated, including the prevalence of mutations in known causal genes, the penetrance and expressivity in
genotyped families, and the utility of the 2010 Task Force criteria in clinical diagnosis. Clinical and molecular genetic
evaluation was performed in 210 first-degree and 45 second-degree relatives from 100 families. In 51 families, the
proband was deceased. The living probands had a high prevalence of ECG abnormalities (89%) and ventricular
arrhythmia (78%) and evidence of more severe disease than relatives. Definite or probable causal mutations were found
in 58% of families and 73% of living probands, of whom 28% had an additional desmosomal variant (ie, mutation or
polymorphism). Ninety-three relatives had a causal mutation; 33% fulfilled the 2010 criteria, whereas only 19% satisfied
the 1994 version (P=0.03). An additional desmosomal gene variant was found in 10% and was associated with a 5-fold
increased risk of developing penetrant disease (odds ratio, 4.7; 95% confidence interval, 1.1 to 20.4; P=0.04).
Conclusions. Arrhythmogenic right ventricular cardiomyopathy is a genetically complex disease characterized by marked
intrafamilial phenotype diversity. Penetrance is definition dependent and is greater with the 2010 criteria compared with
the 1994 criteria. Relatives harboring >1 genetic variant had significantly increased risk of developing clinical disease,
potentially an important determinant of the phenotypic heterogeneity seen within families with arrhythmogenic right
ventricular cardiomyopathy. ABSTRACT 2 Aims. Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited heart muscle disease predominantly caused by mutations in desmosomal protein genes. Lamin A/C gene (LMNA) mutations are associated with dilated cardiomyopathy, conduction abnormalities and high incidence of sudden cardiac death. In this study we screened a large cohort of ARVC patients for LMNA mutations.
Methods and Results. One hundred and eight patients from unrelated families with borderline (n= 27) or definite (n= 81) diagnosis of ARVC were genetically tested for five desmosomal genes and LMNA. Sixty-one (56.5 %) were positive for desmosomal gene mutations. Standard polymerase chain reaction (PCR) amplification of the 12 protein-coding LMNA exons was performed and mutational screening performed by direct sequencing. Four patients (4%) without desmosomal gene mutations carried LMNA variants. Three had severe RV involvement, and during follow-up three died (two suddenly and one from congestive heart failure); all three had conduction abnormalities on resting 12 lead ECG. Myocardial tissue from two patients showed myocyte loss and fibro-fatty replacement. In one of these, immunohistochemical staining with antibody to plakoglobin showed reduced/absent staining of the intercalated discs in the myocardium.
Conclusion. LMNA mutations can be found in severe forms of ARVC. LMNA should be added to desmosomal genes when genetically testing patients with suspected ARVC, particularly when they also have ECG evidence for conduction disease
Trajectory Approximation of a Low-Performance E-Sail with Fixed Orientation
No full textThe Electric Solar Wind Sail (E-sail) is a propellantless propulsion system that converts solar wind dynamic pressure into a deep-space thrust through a grid of long conducting tethers. The first flight test, needed to experience the true potential of the E-sail concept, is likely to be carried out using a single spinning cable deployed from a small satellite, such as a CubeSat. This specific configuration poses severe limitations to both the performance and the maneuverability of the spacecraft used to analyze the actual in situ thruster capabilities. In fact, the direction of the spin axis in a single-tether configuration can be considered fixed in an inertial reference frame, so that the classic sail pitch angle is no longer a control variable during the interplanetary flight. This paper aims to determine the polar form of the propelled trajectory and the characteristics of the osculating orbit of a spacecraft propelled by a low-performance spinning E-sail with an inertially fixed axis of rotation. Assuming that the spacecraft starts the trajectory from a parking orbit that coincides with the Earth’s heliocentric orbit and that its spin axis belongs to the plane of the ecliptic, a procedure is illustrated to solve the problem accurately with a set of simple analytical relations
Solar Sail Missions to Mercury with Venus Gravity Assist
No full textAbstract
Missions towards Mercury are expensive in terms of propellant mass, especially when conventional propulsion systems are considered. Significant propellant mass saving may be obtained with the use of complex multiple intermediate flyby maneuvers, but the corresponding mission time increase is substantial. An interesting option is offered by solar sails that are potentially able to fulfil a Mercury rendezvous mission within reasonable time intervals, without the need of any propellant. In this paper we investigate the solar sail performance for a minimum time mission towards Mercury with a single Venus flyby. This allows us to quantify the improvement (in terms of mission time saving) that such a flyby offers with respect to a classical direct transfer. Also, with the aid of a suitable simplified model of spacecraft mass distribution, we quantify the significant increase in payload mass fraction associated with the flyby maneuver
L'art. 238-bis t.u. Spese di giustizia una nuova spada di Damocle sulla disciplina inerente la procedura di conversione delle pene pecuniarie?
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