Guidance and flight control law development for hypersonic vehicles

During the third reporting period our efforts were focused on a reformulation of the optimal control problem involving active state-variable inequality constraints. In the reformulated problem the optimization is carried out not with respect to all controllers, but only with respect to asymptotic controllers leading to the state constraint boundary. Intimately connected with the traditional formulation is the fact that when the reduced solution for such problems lies on a state constraint boundary, the corresponding boundary layer transitions are of finite time in the stretched time scale. Thus, it has been impossible so far to apply the classical asymptotic boundary layer theory to such problems. Moreover, the traditional formulation leads to optimal controllers that are one-sided, that is, they break down when a disturbance throws the system on the prohibited side of the state constraint boundary

Rapid near-optimal aerospace plane trajectory generation and guidance

Effort was directed toward the problems of the real time trajectory optimization and guidance law development for the National Aerospace Plane (NASP) applications. In particular, singular perturbation methods were used to develop guidance algorithms suitable for onboard, real time implementation. The progress made in this research effort is reported

Improved shaping approach to the preliminary design of low-thrust trajectories

This paper presents a general framework for the development of shape-based approaches to low-thrust trajectory design. A novel shaping method, based on a three-dimensional description of the trajectory in spherical coordinates, is developed within this general framework. Both the exponential sinusoid and the inverse polynomial shaping are demonstrated to be particular two-dimensional cases of the spherical one. The pseudoequinoctial shaping is revisited within the new framework, and the nonosculating nature of the pseudoequinoctial elements is analyzed. A two step approach is introduced to solve the time of flight constraint, related to the design of low-thrust arcs with boundary constraints for both spherical and pseudoequinoctial shaping. The solution derived from the shaping approach is improved with a feedback linear-quadratic controller and compared against a direct collocation method based on finite elements in time. The new shaping approach and the combination of shaping and linear-quadratic controller are tested on three case studies: a mission to Mars, a mission to asteroid 1989ML, a mission to comet Tempel-1, and a mission to Neptune

Le témoignage du Vaticanus gr. 163 pour la période entre 945-963

  A. Μαρκόπουλος Ἡ συμβολὴ  τοῦ  χειρογράφου Vaticanus gr. 163 γιὰ τὴ χρονικὴ περίοδο 945-963 Τὸ χειρόγραφο Vaticanus gr. 163 παραδίδει, ἀνάμεσα σὲ ἄλλα ἱστορικά κείμενα, καὶ μία μορφὴ τῆς χρονογραφίας τοῦ Συμεὼν Λογοθέτη. Ἡ ἰδιαιτερότητα τῆς μορφῆς αὐτῆς εἶναι ὅτι ἡ διήγηση δὲ διακόπτεται μὲ τὸ θάνατο τοῦ Ρωμανοῦ Λακαπηνοῦ, ὅπως συνήθως συμβαίνει μὲ τὰ χειρόγραφα τοῦ Λογοθέτη, ἀλλὰ συνεχίζεται μέχρι τὴν ἀναγόρευση στὸ θρόνο τοῦ Νικηφόρου Φωκᾶ (963). Ἀποτελεῖ ἔτσι σημαντικὴ ἱστορικὴ πηγή για τα γεγονότα αὐτῆς τῆς περιόδου.  Ἡ μελέτη περιλαμβάνει ἔκδοση τῶν φφ. 58ν-61 τοῦ χειρογράφου Vaticanus gr. 163 ποὺ καλύπτουν τὸ χρονικὸ διάστημα μεταξὺ τῶν ἐτῶν 945-963. Ἡ ἔκδοση συνοδεύεται ἀπὸ ἱστορικὸ σχολιασμό.  A. Μαρκόπουλος Ἡ συμβολὴ  τοῦ  χειρογράφου Vaticanus gr. 163 γιὰ τὴ χρονικὴ περίοδο 945-963 Τὸ χειρόγραφο Vaticanus gr. 163 παραδίδει, ἀνάμεσα σὲ ἄλλα ἱστορικά κείμενα, καὶ μία μορφὴ τῆς χρονογραφίας τοῦ Συμεὼν Λογοθέτη. Ἡ ἰδιαιτερότητα τῆς μορφῆς αὐτῆς εἶναι ὅτι ἡ διήγηση δὲ διακόπτεται μὲ τὸ θάνατο τοῦ Ρωμανοῦ Λακαπηνοῦ, ὅπως συνήθως συμβαίνει μὲ τὰ χειρόγραφα τοῦ Λογοθέτη, ἀλλὰ συνεχίζεται μέχρι τὴν ἀναγόρευση στὸ θρόνο τοῦ Νικηφόρου Φωκᾶ (963). Ἀποτελεῖ ἔτσι σημαντικὴ ἱστορικὴ πηγή για τα γεγονότα αὐτῆς τῆς περιόδου.  Ἡ μελέτη περιλαμβάνει ἔκδοση τῶν φφ. 58ν-61 τοῦ χειρογράφου Vaticanus gr. 163 ποὺ καλύπτουν τὸ χρονικὸ διάστημα μεταξὺ τῶν ἐτῶν 945-963. Ἡ ἔκδοση συνοδεύεται ἀπὸ ἱστορικὸ σχολιασμό

Assessing the effectiveness of usability evaluation methods for children

The comparison of three Usability Evaluation Methods (UEM's) is reported with respect to the number of problems uncovered on software products, by children participants. The UEM's compared require different levels of verbalisation of the child that is performing the evaluation. Age of the children, gender, verbal competence, and extroversion level are things that could influence which UEM works best. The outcome of the experiment was that a UEM that requires the children to verbalise a lot is the most effective, and that girls find more problems in the program than boys

Understanding How Users Engage in an Immersive Virtual Reality-Based Live Event

Virtual Reality combined with social functioning is a lucrative business direction. Due to COVID-19, a need for better social interaction is identified urgently both in education institutes and the business sector. In this paper, we will show two business cases where social functioning is needed. The first one illustrates how the business sector can use Virtual Reality Social Platform (VRSP) in remote events. As a case study, we have selected Spinverse’s Summer Day organized in Microsoft AltspaceVR. The second business case, in turn, classifies requirements for Virtual Reality Social platforms. This has been studied in close cooperation with XR Presence. Results show that current technologies offer many features to be used, but at the same time, there are needs for further development. In addition, more studies are needed in technology acceptance, usability, user experience, and business impact

Bose-Einstein Correlations of Three Charged Pions in Hadronic Z^0 Decays

Bose-Einstein Correlations (BEC) of three identical charged pions were studied in 4 x 10^6 hadronic Z^0 decays recorded with the OPAL detector at LEP. The genuine three-pion correlations, corrected for the Coulomb effect, were separated from the known two-pion correlations by a new subtraction procedure. A significant genuine three-pion BEC enhancement near threshold was observed having an emitter source radius of r_3 = 0.580 +/- 0.004 (stat.) +/- 0.029 (syst.) fm and a strength of \lambda_3 = 0.504 +/- 0.010 (stat.) +/- 0.041 (syst.). The Coulomb correction was found to increase the \lambda_3 value by \~9% and to reduce r_3 by ~6%. The measured \lambda_3 corresponds to a value of 0.707 +/- 0.014 (stat.) +/- 0.078 (syst.) when one takes into account the three-pion sample purity. A relation between the two-pion and the three-pion source parameters is discussed.Comment: 19 pages, LaTeX, 5 eps figures included, accepted by Eur. Phys. J.

W+W- production and triple gauge boson couplings at LEP energies up to 183 GeV

A study of W-pair production in e+e- annihilations at Lep2 is presented, based on 877 W+W- candidates corresponding to an integrated luminosity of 57 pb-1 at sqrt(s) = 183 GeV. Assuming that the angular distributions of the W-pair production and decay, as well as their branching fractions, are described by the Standard Model, the W-pair production cross-section is measured to be 15.43 +- 0.61 (stat.) +- 0.26 (syst.) pb. Assuming lepton universality and combining with our results from lower centre-of-mass energies, the W branching fraction to hadrons is determined to be 67.9 +- 1.2 (stat.) +- 0.5 (syst.)%. The number of W-pair candidates and the angular distributions for each final state (qqlnu,qqqq,lnulnu) are used to determine the triple gauge boson couplings. After combining these values with our results from lower centre-of-mass energies we obtain D(kappa_g)=0.11+0.52-0.37, D(g^z_1)=0.01+0.13-0.12 and lambda=-0.10+0.13-0.12, where the errors include both statistical and systematic uncertainties and each coupling is determined setting the other two couplings to the Standard Model value. The fraction of W bosons produced with a longitudinal polarisation is measured to be 0.242+-0.091(stat.)+-0.023(syst.). All these measurements are consistent with the Standard Model expectations.Comment: 48 pages, LaTeX, including 13 eps or ps figures, submitted to European Physical Journal