Submitted by Mario BC (mario@bc.ufrpe.br) on 2018-10-25T12:38:43Z No. of bitstreams: 1 Ana Claudia Villar e Luna Gusmao.pdf: 6720779 bytes, checksum: 0e1605db9188d20cf80950db057b8ac6 (MD5) / Made available in DSpace on 2018-10-25T12:38:43Z (GMT). No. of bitstreams: 1 Ana Claudia Villar e Luna Gusmao.pdf: 6720779 bytes, checksum: 0e1605db9188d20cf80950db057b8ac6 (MD5) Previous issue date: 2017-02-23 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The study, assessment and monitoring of hydrological processes in a river basin are fundamental for an efficient management of water use. In this context, quantifying evapotranspiration is of great relevance considering that it is one of the most important components of a hydrological cycle, because it represents the loss of surface water to the atmosphere and its use by the crops. The objective of this research is to improve the actual evapotranspiration (Etr) provided by the Mu et al. (2007) algorithm. This enhancement will be achieved by the use of meteorological data with higher resolution in modelling, and through a better estimation of the parameters involved in the computation of aerodynamic resistance and the crop. The research was carried out in the Tapacurá Basin in the state of Pernambuco, Northeast Brazil, where an experimental meteorological tower was installed, which served as the basis for the input meteorological data provision, as well as for ETr determination by the energy balance method by the Bowen ratio (BERB). The model was processed from eight-day products (MOD09Q1) between 2011 and 2012. Due to the atmospheric conditions of the Tapacura Basin, which are very cloudy, the selection of cloud-free pixels was performed resulting in a more cleaned image every thirty days. Thus forming a monthly composition of albedo and vegetation indexes (IAF and EVI 2). It was then admitted that these variables remain constant during the month, enabling the determination of daily net radiation (Rn24h) and daily actual evapotranspiration. For the Rn24h, a local calibration of the model proposed by De Bruim (1987) was performed through the CNR4 sensor installed at the site in 2015 and 2016. The calibrated model was used to determine the Rn24h in 2011 and 2012. Through the composition of albedo, solar radiation data, daily atmospheric transmittance and calibration of the Rn24h model, it was possible to obtain results for all of 2011 and 2012. The Rn24h results estimated by remote sensing showed a good correlation with the ones measured at the station (R² = 0.9692, for the year 2011 and R² = 0.9373, for the year 2012). The validation of the ETr by remote sensing by the BERB presented the Mean Absolute Error (EAM), Mean Relative Error (ERM) and Root Mean Square Error (REQM), which were respectively, 0.73 mm day -1, 17, 1% and 0.93 mm day -1 for 2011 and 0.58 mm day -1, 26.8% and 0.70 mm day -1 for 2012. The results were consistent with the literature and showed that the proposed methodology is efficient in studies of spatial and temporal distribution of ETr for the studied region. / O estudo, avaliação e monitoramento de processos hidrológicos em bacias hidrográficas são fundamentais para que haja uma gestão eficaz do uso da água. Diante dessa afirmação, a quantificação dos componentes do balanço hídrico, como a evapotranspiração, é muito importante para um gerenciamento sustentável desse recurso. Tendo em vista a importância desse tema, o objetivo do presente trabalho é o aprimoramento da quantificação da evapotranspiração real (ETr) obtida pelo algoritmo proposto Mu et al. (2007), a partir da utilização de dados meteorológicos de melhor resolução espacial e otimização da estimativa dos parâmetros envolvidos no cômputo das resistências aerodinâmica e da cultura. A pesquisa foi realizada na bacia hidrográfica do rio Tapacurá (estado de Pernambuco, região Nordeste do Brasil), onde foi instalada uma torre meteorológica experimental para fornecer os dados de entrada para alimentar o referido modelo. Outrossim, os dados da estação meteorológica também foram utilizados para validar a ETr pelo método do balanço de energia através da razão de Bowen (BERB). O modelo foi processado a partir de produtos de oito dias (MOD09Q1) entre os anos de 2011 e 2012. Devido às condições atmosféricas da bacia hidrográfica do rio Tapacurá, que são de muita nebulosidade, foi realizada a seleção de pixels livres de nuvens resultando em uma imagem mais limpa a cada trinta dias. Com isso, foi realizada uma composição mensal do albedo e dos índices de vegetação (IAF e EVI 2), necessários para a determinação do saldo de radiação diário (Rn24h) e a evapotranspiração real diária, admitindo que essas variáveis permanecem constantes durante o mês. Para o Rn24h, foi realizada a calibração local do modelo proposto por De Bruim (1987), através do sensor CNR4 instalado no local entre os anos de 2015 e 2016 e calibrados para a determinação do Rn24h nos anos 2011 e 2012. Através da composição do albedo, de dados de radiação solar, da transmitância atmosférica diária e da calibração do modelo do Rn24h, foi possível obter resultados para todos os dias dos anos 2011 e 2012. Os resultados do Rn24h estimado por sensoriamento remoto evidenciaram boa correlação com o medido na estação (R² = 0,97 para o ano de 2011 e R² = 0,94 para o ano de 2012). A validação da ETr por sensoriamento remoto apresentou Erro Absoluto Médio (EAM), Erro Relativo Médio (ERM) e Raiz do Erro Quadrático Médio (REQM) de 0,73 mm dia-1, 17,1% e 0,93 mm dia-1 para o ano de 2011, respectivamente. Para o ano de 2012, os índices estatísticos supracitados foram de 0,58 mm dia-1, 26,8% e 0,70 mm dia-1, respectivamente. Os resultados apresentaram-se condizentes com a literatura e evidenciaram que a metodologia proposta demonstrou eficiência em estudos da distribuição espacial e temporal da ETr para região estudada.

A key challenge in low-thrust trajectory design is generating preliminary solutions that simultaneously detail the evolution of the spacecraft position and velocity vectors, as well as the thrust history. To address this difficulty, a dynamical model that incorporates a low-thrust force into the circular restricted 3-body problem (CR3BP), i.e., the CR3BP+LT, is constructed and analyzed. Control strategies that deliver specific energy changes (including zero energy change to deliver a conservative system) are derived and investigated, and dynamical structures within the CR3BP+LT are explored as candidate solutions to seed initial low-thrust trajectory designs. Furthermore, insights from dynamical systems theory are leveraged to inform the design process. In the combined model, the addition of a low-thrust force modifies the locations and stability of the equilibrium solutions, resulting in flow configurations that differ from the natural behavior in the CR3BP. The application of simplifying assumptions yields a conservative, autonomous system with properties that supply useful insights. For instance, "forbidden regions" at fixed energy levels bound low-thrust motion, and analytical equations are available to guide the navigation through energy space. Linearized dynamics about the equilibria supply hyperbolic and center manifold structures, similar to the ballistic CR3BP. Low-thrust periodic orbits in the vicinity of the equilibrium solutions also admit hyperbolic and center manifolds, providing an even greater number of dynamical structures to be employed in preliminary trajectory designs. Several applications of the structures and insights derived from the CR3BP+LT are presented, including several strategies for transit and capture near the smaller CR3BP primary body. Finally, an interactive trajectory design framework is presented to explore and utilize the structures and insights delivered by this investigation.

Ever since the revolutionary CubeSat form factor took hold in the Aerospace industry, there has been a desire to send them further and further into space. This thesis introduces an optimization approach to deployment that explores new possibilities of interplanetary CubeSats. In this approach there are three categories of objective functions that are defined by the type of trajectory of a “primary” spacecraft, which carries the CubeSat deployer. These categories are flyby, orbiter, and lander. For each category the objective function starts with four design variables. These are the ΔV of the deployer broken up into three component directions and the true anomaly at the time of deployment. The method then calculates the mission specific objective to be minimized and uses Matlab®’s built in gradient-based optimizer, fmincon. The results show that in the flyby category, the CubeSat has a significantly different turning angle than the primary. The CubeSat can even flyby on the opposite side of the planet. In the orbiter case it is shown that the method works by testing it with two objective functions, the difference in inclination and the difference in eccentricity between the primary and the CubeSat. It is shown that the inclination can be changed by 0.1314° and the eccentricity can be changed by 0.0033. These values, although low in magnitude, are an order of magnitude greater than non-optimal deployment scenarios. Still, another optimization method is introduced to find out how much extra ΔV the CubeSat would need to reach a desired change. This shows that with just an extra 75 m/s of ΔV, the CubeSat can change its orbit by 5°. This could come from either a propulsion system or a modified deployer. The final category, lander, used the flight path angle when entering the atmosphere as an objective. The method shows that flight path angle can be changed by 2.6°. Overall, these examples have proven that the method can find optimal solutions to CubeSat deployment scenarios at other planets.

Overcrowding of the Low Earth Orbit (LEO) region is a growing problem. Decades of treating this part of space like a scrap yard has caused it to become a hazardous environment for operating satellites. At present, the largest pieces of debris are being continuously tracked and satellite operators avoid them by maneuvering their spacecrafts out of the way. This approach is not possible for pieces that are smaller than 10 cm, since they are hard to detect and track as well as numerous. The exact number is not known but it is believed to be around 190 000. A number of different mitigation methods have been suggested. In this project the Laser Orbital Debris Removal (LODR) has been investigated and a basic simulation model has been developed. Though many aspects have been studied, only a few have been implemented in this first version of the simulation program. The thesis has uncovered some limiting factors of the models and data that have been used to describe the physical phenomena that relate to this problem. These factors, and other suggestions, are mentioned in chapter 5. Though the model is far from perfected, it shows the technical feasibility of the suggested method, as well as some of the problems that need to be solved before it can be implemented. The fact that it would be possible to build a ground based LODR system, in no way assures that it is likely to occur. The political aspects of such a facility are too problematic at this day in age. How should it be operated? Could we trust that it would not be used as a weapon? The questions are many and the answers are uncertain. For now, it seems best to focus on improving the understanding of the phenomena, the precision of the model and hope that there will come a time when this research will lead to an implementable solution.

The growth in orbital debris has been predicted since the dawn of the space age. Now the debris fields cascade through orbits and the risk of collision is on an infinite upward trajectory. This thesis will examine what impact a wider concept of space security can have our understanding of orbital debris and the space security agenda. The space security agenda is in a state a flux as it seeks the most effective way to deal with the threat posed by orbital debris. A traditionally narrow approach of security would see debris discarded as a security threat due to its limited threat to a state. However, a broader approach would see aspects of environmental security emerge, allowing both public and private sectors to act to solve this crisis. There is a sizeable void in the literature that links policy and science when analysing orbital debris. Therefore, when applying the theory, it is best to find consensus and collaboration. The Copenhagen and Welsh Schools of International Security offer opposing views initially. Nonetheless, when examined closely they reveal similarities that allow for a 'hybrid' theory to emerge. The international challenges to legal and policy changes are diverse and complex. Consequently, the significance of transparency and confidence- building measures to lead space policy and...

This thesis aims to investigate the potential of a transfer orbit using successive aerocaptures at Saturn and Titan to establish a science orbit around Titan. Titan is an Earth-like moon with a dense atmosphere and organic compounds present. It has many similarities with Earth that are useful to study such as superrotation. Superrotation is when the atmosphere rotates faster than the body it surrounds. In order to study Titan, we need to establish an orbit around it. The Saturn system is distant from Earth, 8.5 Astronomical Units (AU) which makes it difficult to reach from a time and velocity point of view. We propose to use an aerocapture at Saturn to intercept Titan with lower relative velocity in order to perform an aerocapture at Titan. The analysis was performed in primarily MATLAB to simulate the orbits. The results of this showed that we can aerocapture a spacecraft at Saturn and arrive at Titan within roughly 4 to 8 km/s relative velocity regardless of the incoming hyperbolic excess velocity at the Saturn system. This can be improve upon by using intermediate transfer orbits, such as bi-elliptics, to arrive with even lower relative velocities to Titan of as low as 1 km/s. The drag acceleration experienced during the Saturn aerocapture had peak values of between 0.2 and 1.4 g's and acceleration over 50% of the peak is experienced between 6.8 and 8 minutes. This capture method has the potential to make Titan more easily accessible and allow for scientific study of a clear target for improving our understanding of Earth-like processes on other bodies in our solar system. / Master of Science / This thesis aims to investigate the potential of a transfer orbit using successive aerocaptures at Saturn and Titan to establish a science orbit around Titan. Aerocapturing is utilizing the atmosphere of a body to slow down a spacecraft. Titan is an Earth-like moon with a dense atmosphere and organic compounds present. It has many similarities with Earth that are useful to study such as superrotation. Superrotation is when the atmosphere of a body rotates faster than the body it surrounds. In order to study Titan, we need to establish an orbit around it. The Saturn system is distant from Earth, 8.5 Astronomical Units (AU) which makes it difficult to reach from a time and velocity point of view. It takes a large amount of time to get there so we attempt to get there faster by increasing velocity. This means we arrive at the Saturn system with a large amount of velocity that we need to counter-act in order to orbit. We propose to use an aerocapture at Saturn to intercept Titan with lower velocity in order to perform another aerocapture at Titan to slow into an orbit. The analysis was performed in primarily MATLAB to simulate the orbits. The results of this showed that we can aerocapture a spacecraft at Saturn and arrive at Titan within roughly 4 to 8 km/s regardless of the incoming velocity to the Saturn system. This can be improve upon by using intermediate transfer orbits, after capturing at Saturn, to arrive with even lower velocities at Titan of as low as 1 km/s. The drag acceleration experienced during the Saturn aerocapture had peak values of between 0.2 and 1.4 g's and acceleration over 50% of the peak is experienced between 6.8 and 8 minutes. This is relatively gentle for an aerocapture and means the spacecraft likely will not require significant structural support. This capture method has the potential to make Titan more easily accessible and allow for scientific study of a clear target for improving our understanding of Earth-like processes on other bodies in our solar system.

A systems engineering approach was used to produce a preliminary design configuration for an ion-propelled orbital transfer vehicle system. The four components of the system are: ground software, ground hardware, the orbital transfer vehicle and the space shuttle. The orbital transfer vehicle uses electrostatic propulsion to transfer payload satellites from a low earth orbit, to any other desired orbit. The system maintenance concept, and a conceptual design are derived from the statement of need and the system operational requirements. The resulting design, maintainability, reliability and support requirements are discussed. A discussion of the feasibility of an ion propelled orbital transfer vehicle is included. / Master of Science

This thesis is aimed at establishing modalities of time-resolved photoelectron spectroscopy (tr-PES) conducted at a free-electron laser (FEL) source and at a high harmonic generation (HHG) source for imaging the motion of atoms, charge and energy at photoexcited hybrid organic/inorganic interfaces. Transfer of charge and energy across interfaces lies at the heart of surface science and device physics and involves a complex interplay between the motion of electrons and atoms. At hybrid organic/inorganic interfaces involving planar molecules, such as pentacene and copper(II)-phthalocyanine (CuPc), atomic motions in out-of-plane direction are particularly apparent. Such hybrid interfaces are of importance to, e.g., next-generation functional devices, smart catalytic surfaces and molecular machines. In this work, two hybrid interfaces – pentacene atop Ag(110) and copper(II)-phthalocyanine (CuPc) atop titanium disulfide (1T-TiSe2) – are characterized by means of modalities of tr-PES. The experiments were conducted at a HHG source and at the FEL source FLASH at Deutsches Elektronen-Synchrotron DESY (Hamburg, Germany). Both sources provide photon pulses with temporal widths of ∼ 100 fs and thus allow for resolving the non-equilibrium dynamics at hybrid interfaces involving both electronic and atomic motion on their intrinsic time scales. While the photon energy at this HHG source is limited to the UV-range, photon energies can be tuned from the UV-range to the soft x-ray-range at FLASH. With this increased energy range, not only macroscopic electronic information can be accessed from the sample’s valence and conduction states, but also site-specific structural and chemical information encoded in the core-level signatures becomes accessible. Here, the combined information from the valence band and core-level dynamics is obtained by performing time- and angle-resolved photoelectron spectroscopy (tr-ARPES) in the UV-range and subsequently performing time-resolved x-ray photoelectron spectroscopy (tr-XPS) and time-resolved photoelectron diffraction (tr-XPD) in the soft x-ray regime in the same experimental setup. The sample’s bandstructure in energy-momentum space and time is captured by a time-of-flight momentum microscope with femtosecond temporal and sub-Ångström spatial resolutions. In the investigated systems, out-of-equilibrium dynamics are traced that are connected to the transfer of charge and energy across the hybrid interfaces. While energetic shifts and complementary population dynamics are observed for molecular and substrate states, the shapes of involved molecular orbitals change in energy-momentum space on a subpicosecond time scale. In combination with theory support, these changes are attributed to iiiatomic reorganizations at the interface and transient molecular structures are reconstructed with sub-Ångström precision. Unique to the material combination of CuPc/TiSe2, a structural rearrangement on the macroscopic scale is traced simultaneously: ∼ 60 % of the molecules undergo a concerted, unidirectional in-plane rotation. This surprising observation and its origin are detailed in this thesis and connected to a particularly efficient charge transfer across the CuPc/TiSe2 interface, resulting in a charging of ∼ 45 % of CuPc molecules. / Das Ziel der vorliegenden Doktorarbeit ist es, die Bewegung von Atomen, Ladungsträgern und Energie an organisch/anorganischen Grenzschichten fernab des thermischen Gleichgewichts zu visualisieren und deren Wechselwirkung zu entschlüsseln. Dies wird experimentell mittels zeitaufgelöster Photoemissionsexperimente an einer Freien-Elektronen-LaserQuelle und an einer Höher-Harmonischen-Quelle verwirklicht. Ladungs- und Energietransfer zwischen organisch/anorganischen Grenzschichten sind zentrale Komponenten für die Funktion Molekül-basierter Anwendungen, wie z.B. katalytische Oberflächen, elektronische Schalt- und Speichergeräte oder molekulare Maschinen. Sie stellen einen dynamischen Prozess dar, der sich in einem Wechselspiel aus der Bewegung von Elektronen zwischen beiden Schichten und atomaren Bewegungen innerhalb beider Schichten äußert. Planare Moleküle, wie Pentacen oder Kupfer(II)-Phthalocyanin (CuPc), eignen sich besonders um solche atomaren Bewegungen zu untersuchen, da diese aufgrund geringer Rückstellkräfte senkrecht zur Molekülebene besonders ausgeprägt sein können. In dieser Arbeit werden Ladungs- und Energietransferprozesse an zwei ausgewählten Grenzschichten untersucht: Pentacen auf Silber (Ag(110)) und CuPc auf Titan Diselenid (1T-TiSe2). Zeitaufgelöste Photoemissionsexperimente (tr-PES) wurden an einer HöherHarmonischen-Quelle und an dem Freien-Elektronen-Laser FLASH (Deutsches Elektronen-Synchrotron DESY, Hamburg, Deutschland) durchgeführt. Beide Lichtquellen liefern Photonenpulse mit einer Halbwertsbreite von etwa 100 fs und sind daher geeignet, um Nicht-Gleichgewichtsprozesse zeitlich aufzulösen, die auf der Bewegung von sowohl Elektronen als auch Atomen basieren. Die gewählte Höher-Harmonische-Quelle liefert Photonenenergien im UV-Bereich. Bei FLASH hingegen können die Photonenenergien variabel vom UV-Bereich bis hin zum Weichröntgenbereich erzeugt werden. Dieser erweiterte Energiebereich ermöglicht es, zusätzlich zur elektronischen Dynamik im Valenzbereich, auch Dynamiken kernnaher Zustände zu beobachten. Mithilfe dreier Modalitäten von zeitaufgelöster Photoemission – zeit- und winkelaufgelöste Photoelektronenspektroskopie (tr-ARPES), zeitaufgelöste Röntgenphotoelektronenspektroskopie (tr-XPS) und zeitaufgelöste Röntgenphotoelektronen-Diffraktion (tr-XPD) – werden sowohl die elektronischen als auch strukturellen Dynamiken der Grenzschicht rekonstruiert. Dabei dient tr-ARPES im UV-Bereich zur Charakterisierung der makroskopischen elektronischen Eigenschaften und tr-XPS und tr-XPD im Weichröntgenbereich dienen zur Analyse lokaler chemischer und struktureller Eigenschaften. Alle Messungen wurden unter denselben experimentellen Beidingungen durchgeführt und mithilfe eines Flugzeit-Impulsmikroskops konnte die transiente Bandstruktur mit einer Ortauflösung im Sub-Ångström-Bereich und einer Zeitauflö- sung im Femtosekunden-Bereich aufgenommen werden. In beiden untersuchten Systemen werden elektronische und strukturelle Prozesse an der Molekül–Substrat Grenzfläche beobachtet, die durch einen Ladungs- und Energietransfer in Folge optischer Anregung erklärt werden. Dieser Transfer äußert sich elektronisch durch ein Befüllen des Substrat-Leitungsbands und einem zeitgleichen Entleeren der MolekülValenzorbitale. Strukturelle Veränderungen, wie die Adsorptionshöhe oder intramolekulare Atompositionen, werden aus den sich zeitgleich verformenden Molekül-Valenzorbitalen rekonstruiert. Speziell für CuPc/TiSe2 wird ein effektiver Ladungstransfer beobachtet, wodurch 375 fs nach optischer Anregung ∼ 45 % der Moleküle einfach positiv geladen vorliegen. Diese Ladungstrennung zwischen den sich wie ein Schachbrett anordnenden positivgeladenen und neutralen Molekülen sowie dem Substrat führt zu einer Modulation des Oberflächenpotentials, welche eine energetische Verschiebung aller Grenzflächenzustände bedingt und intramolekulare Strukturveränderungen sowie eine makroskopische Reorganisation des Molekülfilms zur Folge hat: ∼ 60 % der Moleküle drehen sich innerhalb von ∼ 375 fs synchron auf dem Substrat und nehmen nach ∼ 1800 fs wieder ihre Ausgangsposition ein. Diese überraschende Beobachtung sowie die Ursache werden detaillierter in der vorliegenden Arbeit diskutiert und in den Kontext aktueller Forschung an "molekularen Schaltern" gebracht.

Twisted particles carry Orbital Angular Momentum (OAM), an important property utilized to encode quantum information. The OAM of twisted photons can be trans- ferred onto condensed matter systems in the form of twisted excitons. Numerical solutions of the time-dependent Schr ̈odinger equation for a 3-arm molecular chain are used to demonstrate the manipulation of twisted excitons via an external magnetic field. We present the first design for an OAM transistor in a quasi-1D system that can be used to control the flow of OAM using the magnetic field. The underlying mechanism is the interaction between OAM and the magnetic field which leads to a orbit-resolved Bloch oscillation (ORBO). We present the semi-classical equations of motion for this phenomenon in a one-dimensional system. Unlike classical Bloch oscil- lation, an important effect in ultrafast electron dynamics, the magnet driven ORBO is not limited by electrical breakdown and can easily be observed in natural solids.

No description available.