89,254 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
Automatic goal allocation for a planetary rover with DSmT
No full textIn this chapter, we propose an approach for assigning aninterest level to the goals of a planetary rover. Assigning an interest level to goals, allows the rover to autonomously transform and reallocate the goals. The interest level is defined by data-fusing payload and navigation information. The fusion yields an 'interest map',that quantifies the level of interest of each area around the rover. In this way the planner can choose the most interesting scientific objectives to be analysed, with limited human intervention, and reallocates its goals autonomously. The Dezert-Smarandache Theory of Plausible and Paradoxical Reasoning was used for information fusion: this theory allows dealing with vague and conflicting data. In particular, it allows us to directly model the behaviour of the scientists that have to evaluate the relevance of a particular set of goals. This chaptershows an application of the proposed approach to the generation of a reliable interest map
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
Influence of allosteric Hsp90 ATPase activators on its chaperoning activity
No full textHsp90 is a molecular chaperone with a starring role in the cell life cycle1 and an established anti-apoptotic target in cancer therapy.2 The protein internal dynamics are regulated by ATP and are critical for its function. Hsp90 can be modulated in an allosteric fashion as we have recently demonstrated, targeting the protein C-terminal domain (CTD) with a family of 2-phenyl-benzofuran derivatives.3-5 These compounds accelerate Hsp90 internal dynamics and increase its enzymatic ATPase activity. As a result, they tune its chaperone activity in ways that we are just beginning to unravel.
The synthetic approaches towards an expanded library of about 40 benzofuran derivatives will be presented. The interaction studies with full length Hsp90,6 and the effects on Hsp90 enzymatic and chaperoning activity will be reported for selected compounds.
References
1. S. E. Jackson In Molecular Chaperones; Jackson, S., Ed.; Springer Berlin Heidelberg (2013) Vol. 328, p 155-240.
2. J. Trepel, M. Mollapour, G. Giaccone, and L. Neckers Nat Rev Cancer (2010), 10, 537-549.
3. L. Morelli, A. Bernardi and S. Sattin, Carbohydr. Res. (2014), 390, 33-41.
4. S. Sattin et al Chem. Eur. J. (2015), 21, 13598-13608.
5. G. Vettoretti, E. Moroni, S. Sattin, J. Tao, D.A. Agard, A. Bernardi and G. Colombo Sci Rep (2016), 6, 23830.
6. S. Sattin, M. Panza, F. Vasile, F. Berni, G. Goti, J. Tao, E. Moroni, D.A. Agard, G. Colombo and A. Bernardi
Eur. J.Org. Chem. (2016) DOI: 10.1002/ejoc.201600420
Synthesis and characterization of Hsp90 allosteric activators
No full textHsp90 is a molecular chaperone playing a pivotal role in the cell life cycle1 and an established anti-apoptotic target in cancer therapy.2 The protein internal dynamics are regulated by ATP and are critical for its function. We have recently demonstrated that Hsp90 can be modulated in an allosteric fashion, targeting the protein C-terminal domain (CTD) with a family of 2-phenyl-benzofuran derivatives.3-5 These molecules increase Hsp90 ATPase rate and accelerate its internal dynamics. As a result they tune its chaperone activity in ways that we are just beginning to unravel.
The synthetic approaches towards an expanded library of about 40 benzofuran derivatives diversified at positions R1 and R2 (Figure 1) will be presented together with the interaction studies with full length Hsp90.6
Figure 1: 2-phenyl-benzofuran diversification at positions R1 and R2.
1) Jackson, S. E. In Molecular Chaperones; Jackson, S., Ed.; Springer Berlin Heidelberg: 2013; Vol. 328, p 155-240.
2) Trepel, J.; Mollapour, M.; Giaccone, G. and Neckers, L., Nat Rev Cancer 2010, 10, 537-549.
3) Morelli, L.; Bernardi, A. and Sattin, S.*, Carbohydr. Res. 2014, 390, 33-41.
4) Sattin, S. et al Chem. Eur. J. 2015, 21, 13598-13608.
5) Vettoretti, G; Moroni, E.; Sattin, S.; Tao, J.; Agard, D. A.;. Bernardi, A. and Colombo, G. Sci Rep 2016, 6, 23830.
6) Sattin, S.*; Panza, M.; Vasile, F.; Berni, F.; Goti, G.; Tao, J.; Moroni, E.; Agard, D.; Colombo, G. and Bernardi, A. Eur. J.Org. Chem. 2016 DOI: 10.1002/ejoc.201600420
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
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
On the detection of nearly optimal solutions in the context of single-objective space mission design problems
No full textWhen making decisions, having multiple options available for a possible realization of the same project can be advantageous. One way to increase the number of interesting choices is to consider, in addition to the optimal solution x*, also nearly optimal or approximate solutions; these alternative solutions differ from x* and can be in different regions – in the design space – but fulfil certain proximity to its function value f(x*). The scope of this article is the efficient computation and discretization of the set E of e–approximate solutions for scalar optimization problems. To accomplish this task, two strategies to archive and update the data of the search procedure will be suggested and investigated. To make emphasis on data storage efficiency, a way to manage significant and insignificant parameters is also presented. Further on, differential evolution will be used together with the new archivers for the computation of E. Finally, the behaviour of the archiver, as well as the efficiency of the resulting search procedure, will be demonstrated on some academic functions as well as on three models related to space mission design
Determination of Structural Ensembles of Flexible Molecules in Solution from NMR Data Undergoing Spin Diffusion
No full textSpin diffusion is a formidable problem when interpreting NMR data of chemical compounds. We developed a method to reconstruct the conformational ensemble of flexible molecules displaying spin diffusion, which minimizes the subjective bias in the interpretation of experimental data and which can be used routinely to obtain sets of structures with the correct thermodynamic weights. We showed in the case of a flexible molecule that the correct conformational ensemble is quite different from that obtained with standard methods
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