Contributions to Libration Orbit Mission Design using Hyperbolic Invariant Manifolds

Aquesta tesi doctoral està emmarcada en el camp de l'astrodinàmica. Presenta solucions a problemes identificats en el disseny de missions que utilitzen òrbites entorn dels punts de libració, fent servir la teoria de sistemes dinàmics.El problema restringit de tres cossos és un model per estudiar el moviment d'un cos de massa infinitessimal sota l'atracció gravitatòria de dos cossos molt massius. Els cinc punts d'equilibri d'aquest model, en especial L1 i L2, han estat motiu de nombrosos estudis per aplicacions pràctiques en les últimes dècades (SOHO, Genesis...). Genèricament, qualsevol missió en òrbita al voltant del punt L2 del sistema Terra-Sol es veu afectat per ocultacions degudes a l'ombra de la Terra. Si l'òrbita és al voltant de L1, els eclipsis són deguts a la forta influència electromagnètica del Sol. D'entre els diferents tipus d'òrbites de libració, les òrbites de Lissajous resulten de la combinació de dues oscil.lacions perpendiculars. El seu principal avantatge és que les amplituds de les oscil.lacions poden ser escollides independentment i això les fa adapatables als requeriments de cada missió. La necessitat d'estratègies per evitar eclipsis en òrbites de Lissajous entorn dels punts L1 i L2 motivaren la primera part de la tesi. En aquesta part es presenta una eina per la planificació de maniobres en òrbites de Lissajous que no només serveix per solucionar el problema d'evitar els eclipsis, sinó també per trobar trajectòries de transferència entre òrbites d'amplituds diferents i planificar rendez-vous. Per altra banda, existeixen canals de baix cost que uneixen els punts L1 i L2 d'un sistema donat i representen una manera natural de transferir d'una regió de libració a l'altra. Gràcies al seu caràcter hiperbòlic, una òrbita de libració té uns objectes invariants associats: les varietats estable i inestable. Si tenim present que la varietat estable està formada per trajectòries que tendeixen cap a l'òrbita a la qual estan associades quan el temps avança, i que la varietat inestable fa el mateix però enrera en el temps, una intersecció entre una varietat estable i una d'inestable proporciona un camí asimptòtic entre les òrbites corresponents. Un mètode per trobar connexions d'aquest tipus entre òrbites planes entorn de L1 i L2 es presenta a la segona part de la tesi, i s'hi inclouen els resultats d'aplicar aquest mètode als casos dels problemes restringits Sol Terra i Terra-Lluna.La idea d'intersecar varietats hiperbòliques es pot aplicar també en la cerca de camins de baix cost entre les regions de libració del sistema Sol-Terra i Terra-Lluna. Si existissin camins naturals de les òrbites de libració solars cap a les lunars, s'obtindria una manera barata d'anar a la Lluna fent servir varietats invariants, cosa que no es pot fer de manera directa. I a l'inversa, un camí de les regions de libració lunars cap a les solars permetria, per exemple, que una estació fos col.locada en òrbita entorn del punt L2 lunar i servís com a base per donar servei a les missions que operen en òrbites de libració del sistema Sol-Terra. A la tercera part de la tesi es presenten mètodes per trobar trajectòries de baix cost que uneixen la regió L2 del sistema Terra-Lluna amb la regió L2 del sistema Sol-Terra, primer per òrbites planes i més endavant per òrbites de Lissajous, fent servir dos problemes de tres cossos acoblats. Un cop trobades les trajectòries en aquest model simplificat, convé refinar-les per fer-les més realistes. Una metodologia per obtenir trajectòries en efemèrides reals JPL a partir de les trobades entre òrbites de Lissajous en el model acoblat es presenta a la part final de la tesi. Aquestes trajectòries necessiten una maniobra en el punt d'acoblament, que és reduïda en el procés de refinat, arribant a obtenir trajectòries de cost zero quan això és possible.This PhD. thesis lies within the field of astrodynamics. It provides solutions to problems which have been identified in mission design near libration points, by using dynamical systems theory. The restricted three body problem is a well known model to study the motion of an infinitesimal mass under the gravitational attraction of two massive bodies. Its five equilibrium points, specially L1 and L2, have been the object of several studies aimed at practical applications in the last decades (SOHO, Genesis...). In general, any mission in orbit around L2 of the Sun-Earth system is affected by occultations due to the shadow of the Earth. When the orbit is around L1, the eclipses are caused by the strong electromagnetic influence of the Sun. Among all different types of libration orbits, Lissajous type ones are the combination of two perpendicular oscillations. Its main advantage is that the amplitudes of the oscillations can be chosen independently and this fact makes Lissajous orbits more adaptable to the requirements of each particular mission than other kinds of libration motions. The need for eclipse avoidance strategies in Lissajous orbits around L1 and L2 motivated the first part of the thesis. It is in this part where a tool for planning maneuvers in Lissajous orbits is presented, which not only solves the eclipse avoidance problem, but can also be used for transferring between orbits having different amplitudes and for planning rendez-vous strategies.On the other hand, there exist low cost channels joining the L1 and L2 points of a given sistem, which represent a natural way of transferring from one libration region to the other one. Furthermore, there exist hyperbolic invariant objects, called stable and unstable manifolds, which are associated with libration orbits due to their hyperbolic character. If we bear in mind that the stable manifold of a libration orbit consists of trajectories which tend to the orbit as time goes by, and that the unstable manifold does so but backwards in time, any intersection between a stable and an unstable manifold will provide an asymptotic path between the corresponding libration orbits. A methodology for finding such asymptotic connecting paths between planar orbits around L1 and L2 is presented in the second part of the dissertation, including results for the particular cases of the Sun-Earth and Earth-Moon problems. Moreover, the idea of intersecting hyperbolic manifolds can be applied in the search for low cost paths joining the libration regions of different problems, such as the Sun-Earth and the Earth-Moon ones. If natural paths from the solar libration regions to the lunar ones was found, it would provide a cheap way of transferring to the Moon from the vicinity of the Earth, which is not possible in a direct way using invariant manifolds. And the other way round, paths from the lunar libration regions to the solar ones would allow for the placement of a station in orbit around the lunar L2, providing services to solar libration missions, for instance. In the third part of the thesis, a methodology for finding low cost trajectories joining the lunar L2 region and the solar L2 region is presented. This methodology was developed in a first step for planar orbits and in a further step for Lissajous type orbits, using in both cases two coupled restricted three body problems to model the Sun-Earth-Moon spacecraft four body problem. Once trajectories have been found in this simplified model, it is convenient to refine them to more realistic models. A methodology for obtaining JPL real ephemeris trajectories from the initial ones found in the coupled models is presented in the last part of the dissertation. These trajectories need a maneuver at the coupling point, which can be reduced in the refinement process until low cost connecting trajectories in real ephemeris are obtained (even zero cost, when possible).Postprint (published version

Comprehension of Yes/No- and Wh-questions Across Autism Spectrum Conditions

[eng] Understanding questions is key for successful communication. Although deficits in communication are the hallmark of Autism Spectrum Conditions (ASC), how both yes/no-questions and wh-questions are understood by children with ASC has been poorly investigated in Spanish. Nevertheless, questions play an important role in ASC diagnostic tests and neurocognitive assessments. Although there is a widespread assumption of visual support easing linguistic production and comprehension, it has not been extensively investigated in question comprehension research. The aim of this thesis is to contribute to a more comprehensive picture of language impairments in ASC by targeting questions as a specific and neglected dimension of language in ASC. Specific research questions concern the impact of syntactic differences in question type, syntactic complexity and other linguistic, cognitive and age factors on question comprehension. Finally, the role of visual support as a facilitator of question comprehension is investigated. 34 children with ASC–ID (autism without intellectual disability, mean age = 9.99) were recruited and matched on VMA (verbal mental age) with 34 TD (typically developing) participants (mean age = 8.85). 14 individuals with ASC+ID (autism with intellectual disability, mean age = 12.95) were also recruited. These were compared to 7 ID (intellectual disability) participants without ASC (mean age = 12.86). The task design of the experiment used narratives to control the context in which yes/no-questions and different types of wh-questions (namely wh-questions in simple and complex sentences, long-distance wh-questions in complex sentences and local wh-questions in complex sentences) were asked. Participants responded immediately after having been exposed to narratives with either visual support or audio support only. Participants’ ability to answer questions about these narratives was assessed as a measure of their question comprehension. Significant results showed that both ASC and TD groups had greater difficulties in wh-questions than yes/no-questions. Compared to TD, ASC–ID also had lower wh- question comprehension. In addition, the ASC+ID group showed a lower level of question comprehension in yes/no-questions and in wh-questions compared to the ASC– ID and ID groups. All wh-questions in complex sentences and local wh-questions in complex sentences were more difficult for the ASC–ID group in comparison to the TD group. The ASC+ID group underperformed in all types of wh-question comprehension in comparison to the ASC–ID participants and had greater difficulties to comprehend local wh-questions in complex sentences compared to the ID group. Visual support aided question comprehension both in ASC and in TD. In between- group comparisons significantly greater question comprehension difficulties in tasks with visual support in the ASC–ID relative to the TD group remained. The ASC+ID group scored significantly lower in both visual and non-visual tasks in comparison to both ASC– ID and ID groups. VMA and VIQ (verbal intelligence quotient) correlated with yes/no- question comprehension in TD and in ASC–ID participants. In TD individuals, there was a correlation with these variables and wh-question comprehension. In the ID group, working memory and VIQ had a positive relation with the comprehension of some types of wh-questions. These results provide novel evidence for a question comprehension impairment in ASC with and without ID, which specifically centers on wh-questions. As age and cognitive factors were more related to question comprehension in TD and ID groups than in ASC, different underlying cognitive mechanisms might be at work in ASC. At a practical level, this thesis incites reflection on the roles of question types both in diagnostic assessments and interventions.[cat] La comprensió de les preguntes és essencial per a la comunicació. Tot i que els dèficits en la comunicació són característics de les Condicions de l’Espectre Autista (CEA), la comprensió de les preguntes sí/no i de les preguntes qu- ha estat poc investigada en castellà. Tampoc s’ha estudiat l’impacte del suport visual, encara que es pressuposa que és beneficiós. L’objectiu d’aquest estudi és demostrar com el tipus de pregunta, la complexitat sintàctica i altres factors lingüístics, cognitius i d’edat així com també el suport visual poden influenciar la comprensió d’estructures interrogatives. Amb aquesta finalitat, es van seleccionar 34 persones amb CEA–DI (autisme sense discapacitat intel·lectual, edat mitjana = 9,99), 34 persones amb DT (desenvolupament típic) edat mitjana = 8,85), 14 individus amb CEA+DI (autisme amb discapacitat intel·lectual, edat mitjana = 12,95) i 7 participants amb DI (discapacitat intel·lectual) sense CEA (edat mitjana = 12,86). Es va relacionar el grup amb CEA–DI i el grup amb DT segons l’edat verbal mental. Tant els grups amb CEA com amb DT van tenir més dificultats en la comprensió de les preguntes qu- que en les preguntes sí/no. Comparativament, el grup amb DT respecte del grup amb CEA–DI va mostrar un nivell de comprensió significativament menor de les preguntes qu-. El grup amb CEA+DI va mostrar un dèficit més elevat tant en les preguntes sí/no com en les qu- en comparació amb els grups amb CEA–DI i DI. Totes les preguntes qu- en frases complexes i les preguntes qu- locals en aquestes frases van ser significativament més difícils per al grup amb CEA–DI que per al grup amb DT. El suport visual va afavorir la comprensió de preguntes tant de les persones amb CEA, com del grup amb DT. Altres factors lingüístics, cognitius o d’edat mostren escasses correlacions i complexes amb la comprensió de preguntes, en el CEA. Aquests resultats demostren dèficits en la comprensió de preguntes en tot l’espectre autista, fins i tot en absència de discapacitat intel·lectual

Homoclinic and heteroclinic transfer trajectories between Lyapunov orbits in the Sun-Earth and Earth-Moon systems

In this paper a method for finding homoclinic and heteroclinic connections between Lyapunov orbits using invariant manifolds in a given energy surface of the planar restricted circular three body problem is developed. Moreover, the systematic application of this method to a range of Jacobi constants provides a classification of the connections in bifurcation families. The models used correspond to the Sun-Earth+Moon and the Earth-Moon cases

Contributions to Libration Orbit Mission Design using Hyperbolic Invariant Manifolds

Aquesta tesi doctoral està emmarcada en el camp de l'astrodinàmica. Presenta solucions a problemes identificats en el disseny de missions que utilitzen òrbites entorn dels punts de libració, fent servir la teoria de sistemes dinàmics.El problema restringit de tres cossos és un model per estudiar el moviment d'un cos de massa infinitessimal sota l'atracció gravitatòria de dos cossos molt massius. Els cinc punts d'equilibri d'aquest model, en especial L1 i L2, han estat motiu de nombrosos estudis per aplicacions pràctiques en les últimes dècades (SOHO, Genesis...). Genèricament, qualsevol missió en òrbita al voltant del punt L2 del sistema Terra-Sol es veu afectat per ocultacions degudes a l'ombra de la Terra. Si l'òrbita és al voltant de L1, els eclipsis són deguts a la forta influència electromagnètica del Sol. D'entre els diferents tipus d'òrbites de libració, les òrbites de Lissajous resulten de la combinació de dues oscil.lacions perpendiculars. El seu principal avantatge és que les amplituds de les oscil.lacions poden ser escollides independentment i això les fa adapatables als requeriments de cada missió. La necessitat d'estratègies per evitar eclipsis en òrbites de Lissajous entorn dels punts L1 i L2 motivaren la primera part de la tesi. En aquesta part es presenta una eina per la planificació de maniobres en òrbites de Lissajous que no només serveix per solucionar el problema d'evitar els eclipsis, sinó també per trobar trajectòries de transferència entre òrbites d'amplituds diferents i planificar rendez-vous. Per altra banda, existeixen canals de baix cost que uneixen els punts L1 i L2 d'un sistema donat i representen una manera natural de transferir d'una regió de libració a l'altra. Gràcies al seu caràcter hiperbòlic, una òrbita de libració té uns objectes invariants associats: les varietats estable i inestable. Si tenim present que la varietat estable està formada per trajectòries que tendeixen cap a l'òrbita a la qual estan associades quan el temps avança, i que la varietat inestable fa el mateix però enrera en el temps, una intersecció entre una varietat estable i una d'inestable proporciona un camí asimptòtic entre les òrbites corresponents. Un mètode per trobar connexions d'aquest tipus entre òrbites planes entorn de L1 i L2 es presenta a la segona part de la tesi, i s'hi inclouen els resultats d'aplicar aquest mètode als casos dels problemes restringits Sol Terra i Terra-Lluna.La idea d'intersecar varietats hiperbòliques es pot aplicar també en la cerca de camins de baix cost entre les regions de libració del sistema Sol-Terra i Terra-Lluna. Si existissin camins naturals de les òrbites de libració solars cap a les lunars, s'obtindria una manera barata d'anar a la Lluna fent servir varietats invariants, cosa que no es pot fer de manera directa. I a l'inversa, un camí de les regions de libració lunars cap a les solars permetria, per exemple, que una estació fos col.locada en òrbita entorn del punt L2 lunar i servís com a base per donar servei a les missions que operen en òrbites de libració del sistema Sol-Terra. A la tercera part de la tesi es presenten mètodes per trobar trajectòries de baix cost que uneixen la regió L2 del sistema Terra-Lluna amb la regió L2 del sistema Sol-Terra, primer per òrbites planes i més endavant per òrbites de Lissajous, fent servir dos problemes de tres cossos acoblats. Un cop trobades les trajectòries en aquest model simplificat, convé refinar-les per fer-les més realistes. Una metodologia per obtenir trajectòries en efemèrides reals JPL a partir de les trobades entre òrbites de Lissajous en el model acoblat es presenta a la part final de la tesi. Aquestes trajectòries necessiten una maniobra en el punt d'acoblament, que és reduïda en el procés de refinat, arribant a obtenir trajectòries de cost zero quan això és possible.This PhD. thesis lies within the field of astrodynamics. It provides solutions to problems which have been identified in mission design near libration points, by using dynamical systems theory. The restricted three body problem is a well known model to study the motion of an infinitesimal mass under the gravitational attraction of two massive bodies. Its five equilibrium points, specially L1 and L2, have been the object of several studies aimed at practical applications in the last decades (SOHO, Genesis...). In general, any mission in orbit around L2 of the Sun-Earth system is affected by occultations due to the shadow of the Earth. When the orbit is around L1, the eclipses are caused by the strong electromagnetic influence of the Sun. Among all different types of libration orbits, Lissajous type ones are the combination of two perpendicular oscillations. Its main advantage is that the amplitudes of the oscillations can be chosen independently and this fact makes Lissajous orbits more adaptable to the requirements of each particular mission than other kinds of libration motions. The need for eclipse avoidance strategies in Lissajous orbits around L1 and L2 motivated the first part of the thesis. It is in this part where a tool for planning maneuvers in Lissajous orbits is presented, which not only solves the eclipse avoidance problem, but can also be used for transferring between orbits having different amplitudes and for planning rendez-vous strategies.On the other hand, there exist low cost channels joining the L1 and L2 points of a given sistem, which represent a natural way of transferring from one libration region to the other one. Furthermore, there exist hyperbolic invariant objects, called stable and unstable manifolds, which are associated with libration orbits due to their hyperbolic character. If we bear in mind that the stable manifold of a libration orbit consists of trajectories which tend to the orbit as time goes by, and that the unstable manifold does so but backwards in time, any intersection between a stable and an unstable manifold will provide an asymptotic path between the corresponding libration orbits. A methodology for finding such asymptotic connecting paths between planar orbits around L1 and L2 is presented in the second part of the dissertation, including results for the particular cases of the Sun-Earth and Earth-Moon problems. Moreover, the idea of intersecting hyperbolic manifolds can be applied in the search for low cost paths joining the libration regions of different problems, such as the Sun-Earth and the Earth-Moon ones. If natural paths from the solar libration regions to the lunar ones was found, it would provide a cheap way of transferring to the Moon from the vicinity of the Earth, which is not possible in a direct way using invariant manifolds. And the other way round, paths from the lunar libration regions to the solar ones would allow for the placement of a station in orbit around the lunar L2, providing services to solar libration missions, for instance. In the third part of the thesis, a methodology for finding low cost trajectories joining the lunar L2 region and the solar L2 region is presented. This methodology was developed in a first step for planar orbits and in a further step for Lissajous type orbits, using in both cases two coupled restricted three body problems to model the Sun-Earth-Moon spacecraft four body problem. Once trajectories have been found in this simplified model, it is convenient to refine them to more realistic models. A methodology for obtaining JPL real ephemeris trajectories from the initial ones found in the coupled models is presented in the last part of the dissertation. These trajectories need a maneuver at the coupling point, which can be reduced in the refinement process until low cost connecting trajectories in real ephemeris are obtained (even zero cost, when possible)

Mètodes d'atordiment a escorxador

Treball presentat a l'assignatura de Deontologia i Veterinària Legal (21223

Chapter Biofilm Formation in Uropathogenic Escherichia coli Strains: Relationship with Urovirulence Factors and Antimicrobial Resistance

Medical imagin

High throughput determination log Po/w/pKa/log Do/w of drugs by combination of UHPLC and CE methods

n 1997Valkó et al. developed a generic fast gradient HPLC method, based on the calculation of the Chromatographic Hydrophobicity Index (CHI) from the gradient retention times, in order to measure lipophilicity. We have employedthe correlations between CHI and log Po/wand adapted the rapid gradient HPLC method to UHPLC obtaining excellent resolution and repeatability in a short analysis time (<4min). log Po/wvalues can be easily obtained from these CHI measurementsbut, unfortunately, these correlations are only valid for non-ionized compounds. Consequently, in order to determine the effective log Po/wvalue at a particular pH, afast high-throughput method for pKadeterminationwas required. The IS-CE method, based on the use of internal standards (IS) and capillaryelectrophoresis(CE),is a fast and attractive alternative to other methods for pKadetermination,since itoffers multiple advantages compared to them: low amounts of test compounds and reagents are needed, high purity is not required, specific interactions between test compounds and buffers are corrected, etc. In addition, it allows the determination of a pKavalue in less than 5 minutes. Both CHI and IS-CE have beencombined in order to describe a high throughput alternative in thedetermination ofthe lipophilicity profiles of bioactive compounds

Vascular aging : facts and factors

"Man is as old as his arteries". This old aphorism has been widely confirmed by epidemiological and observational studies establishing that cardiovascular diseases can be age-related in terms of their onset and progression. Besides, with aging come a number of physiological and morphological changes that alters cardiovascular function and lead to subsequently increased risk of cardiovascular disease, even in health asymptomatic individuals. Even though different adaptive mechanisms to protect blood vessels against mild stress have been described, the aging process induces a progressive failure of protective mechanisms, leading to vascular changes. The outcomes of the aging-related modifications are the impairment of homeostasis of the irrigated organs and resultant target organ damage

Transient Mesenteric Ischemia Leads to Remodeling of Rat Mesenteric Resistance Arteries

Mesenteric ischemia/reperfusion (I/R) is associated with high rates of morbidity and mortality. We studied the effect of mesenteric I/R on structural and mechanical properties of rat mesenteric resistance artery (MRA) that, once disrupted, might impact the outcome of this devastating clinical condition. Superior mesenteric artery from Wistar–Kyoto rats was occluded (90 min) and reperfused (24 h). The effect of tezosentan, a dual endothelin (ET)-receptor antagonist, was studied in ischemic (IO) and sham-operated (SO) animals. MRA structure and mechanics were assessed by pressure myography. Nuclei distribution, elastin content and organization, collagen I/III and ET-1 expression, ET-1 plasma levels, superoxide anion (O2⋅−) production, and mRNA levels of NAD(P)H-oxidase subunits were measured. To assess ET-1 effects on O2⋅− production, MRA from non-operated rats were incubated in culture medium with ET-1. Mesenteric I/R increased MRA wall thickness (P < 0.05) and cross-sectional area (P < 0.05) but decreased wall stiffness (P < 0.05). Arterial remodeling was paralleled by enhancement of: (i) collagen I/III expression (P < 0.01), ET-1 expression (P < 0.05), and O2⋅− formation (P < 0.01) in the vessel wall; (ii) number of internal elastic lamina (IEL) fenestrae (P < 0.05); and (iii) plasma levels of ET-1 (P < 0.05). Moreover, ET-1 increased O2⋅− (P < 0.05) production in cultured MRA. Tezosentan prevented hypertrophic remodeling and collagen I/III deposition, and enhanced O2⋅− production, but it did not affect the decreased wall stiffness after mesenteric I/R. These results indicate that 90 min occlusion/24 h reperfusion induces hypertrophic remodeling of MRA linked to ET-1-mediated increase of collagen and O2⋅−. Decreased stiffness may be associated with increased number of IEL fenestrae. The resulting MRA remodeling, initially adaptive, might become maladaptive contributing to the pathology and poor outcome of mesenteric I/R, and might be a valuable treatment target for mesenteric I/R