179,887 research outputs found
A hybrid multiagent approach for global trajectory optimization
No full textIn this paper we consider a global optimization method for space trajectory design problems. The method, which actually aims at finding not only the global minimizer but a whole set of low-lying local minimizers(corresponding to a set of different design options), is based on a domain
decomposition technique where each subdomain is evaluated through a procedure based on the evolution of a population of agents. The method is applied to two space trajectory design problems and compared with existing deterministic and stochastic global optimization methods
Optimal impact strategies for asteroid deflection
No full textThis paper presents an analysis of optimal impact strategies to deflect potentially dangerous asteroids. To compute
the increase in the minimum orbit intersection distance of the asteroid due to an impact with a spacecraft, simple
analytical formulas are derived from proximal motion equations. The proposed analytical formulation allows for an
analysis of the optimal direction of the deviating impulse transferred to the asteroid. This ideal optimal direction
cannot be achieved for every asteroid at any time; therefore, an analysis of the optimal launch opportunities for deviating
a number of selected asteroids was performed through the use of a global optimization procedure. The results in
this paper demonstrate that the proximal motion formulation has very good accuracy in predicting the actual deviation
and can be used with any deviation method because it has general validity. Furthermore, the characterization of
optimal launch opportunities shows that a significant deviation can be obtained even with a small spacecraft
Youths on labour market.Features. Particularities. Pro-mobility factors for graduates. Elements of a balanced policy for labour migration
No full textThe youths’ labour market, and especially insertion employment has a series of particularities defined by aspects such as: flexibility, efficient employment, interest for career but also informal employment, external mobility, including brain drain, segmentation, employment precariousness, income disadvantages, etc. Therefore, also the labour market policy and particularly managing labour mobility especially through the economic and social effects that might be triggered on the local labour market in the origin country, presents a special importance under the conditions of the economic turnaround stage, by promoting new and sustainable jobs, based on knowledge and competences. In the present paper an analysis is made about the youths’ labour market features, and the outcomes of an empirical analysis about graduates’ migration propensity are presented. Suggestions are made for developing a balanced policy for youths’ labour mobility to the benefit of the country of origin.youth employment, labour force mobility, labour migration/mobility management
Direct lunar descent optimisation by finite elements in time approach
No full textIn this paper a direct approach to trajectory optimisation, based on Finite Elements in Time (FET) discretisation is presented. Trajectory optimisation is performed combining the effectiveness and flexibility of Finite Elements in Time in solving complex boundary values problems with a common nonlinear programming algorithm. In order to avoid low accuracy proper to direct approaches, a mesh adaptivity strategy is implemented which exploits the ability of finite elements to represent both continuous and discontinuous functions. The effectiveness and accuracy of direct transcription by FET are proved by a selected number of sample problems. Finally an optimal landing manoeuvre is presented to show the power of the proposed approach in solving even complex and realistic problems
Dynamical Casimir-Polder force between an atom and a conducting wall
No full textThe time-dependent Casimir-Polder force arising during the time evolution of an initially bare two-level atom, interacting with the radiation field and placed near a perfectly conducting wall, is considered. Initially the electromagnetic field is supposed to be in the vacuum state and the atom in its ground state. The analytical expression of the force as a function of time and atom-wall distance is evaluated from the time-dependent atom-field interaction energy. Physical features and limits of validity of the results are discussed in detail
Săpăturile de la Buda (r. Buhuşi, reg. Bacău) / Les fouilles de Buda
No full textCăpitanu Viorel, Buzdugan C., Ursache Vasile. Săpăturile de la Buda (r. Buhuşi, reg. Bacău) / Les fouilles de Buda. In: Materiale şi cercetări arheologice, N°8 1962. pp. 141-144
Cercetări arheologice de suprafaţă la sud de Bucureşti / Recherches archéologiques de surface, au sud de Bucarest
No full textChirica Vasile, Popovici-Baltă R. Cercetări arheologice de suprafaţă la sud de Bucureşti / Recherches archéologiques de surface, au sud de Bucarest. In: Materiale şi cercetări arheologice, N°10 1973. pp. 353-366
Interception and deviation of near earth objects via solar collector strategy
No full textA solution to the asteroid deviation problem via a low-thrust strategy is proposed. This formulation makes use of the proximal motion equations and a semi-analytical solution of the Gauss planetary equations. The average of the variation of the orbital elements is computed, together with an approximate expression of their periodic evolution. The interception and the deflection phase are optimised together through a global search. The low-thrust transfer is preliminary designed with a shape based method; subsequently the solutions are locally refined through the Differential Dynamic Programming approach. A set of optimal solutions are presented for a deflection mission to Apophis, together with a representative trajectory to Apophis including the Earth escape
Subjective Right in the Context of legal Relationship
No full textThis article is trying to treat in its own manner a theme with deep implications in legal life and more exactly individuals, owner of subjective rights in the legal report, putting accent on the problem of birth and end of its legal personality.Subjective right, legal report, individual, legal personality, legal capacity of exercise, legal capacity of use.
Semi-analytical solution for the optimal low-thrust deflection of near-Earth objects
No full textThis paper presents a semi-analytical solution of the asteroid deviation problem when a low-thrust action, inversely proportional to the square of the distance from the sun, is applied to the asteroid. The displacement of the asteroid at the minimum orbit interception distance from the Earth's orbit is computed through proximal motion equations as a function of the variation of the orbital elements. A set of semi-analytical formulas is then derived to compute the variation of the elements: Gauss planetary equations are averaged over one orbital revolution to give the secular variation of the elements, and their periodic components are approximated through a trigonometric expansion. Two formulations of the semi-analytical formulas, latitude and time formulation, are presented along with their accuracy against a full numerical integration of Gauss equations. It is shown that the semi-analytical approach provides a significant savings in computational time while maintaining a good accuracy. Finally, some examples of deviation missions are presented as an application of the proposed semi-analytical theory. In particular, the semi-analytical formulas are used in conjunction with a multi-objective optimization algorithm to find the set of Pareto-optimal mission options that minimizes the asteroid warning time and the spacecraft mass while maximizing the orbital deviation
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