Recursos de colección

Archivo Digital UPM (107.543 recursos)

This is an institutional repository providing access to the research output of the institution. Primarily contains thesis.

Materia = Física

Mostrando recursos 1 - 20 de 1.290

  1. PIC computation of electron current collection to a moving bare tether in the mesothermal condition

    Onishi, Tatsuo; Martínez-Sánchez, Manuel; Cooke, David L.; Sanmartín Losada, Juan Ramón
    In tethered satellite technology, it is important to estimate how many electrons a spacecraft can collect from its ambient plasma by a bare electrodynamic tether. The analysis is however very difficult because of the small but significant Geo-magnetic field and the spacecraft’s relative motion to both ions and electrons. The object of our work is the development of a numerical method, for this purpose. Particle-In-Cell (PIC) method, for the calculation of electron current to a positive bare tether moving at orbital velocity in the ionosphere, i.e. in a flowing magnetized plasma under Maxwellian collisionless conditions. In a PIC code, a...

  2. A review of electrodynamic tethers for space applications

    Sanmartín Losada, Juan Ramón; Lorenzini, Enrico C.; Martínez Sánchez, Manuel
    Space applications of electrodynamic tethers, and basic issues and constraints on their operation are reviewed. The status of the bare-tether solution to the problem of effective electron collection from a rarefied magnetized plasma is revisited. Basic modes of tether operation are analyzed; design parameters and parametric domains where a bare electrodynamic tether is most efficient in deorbiting, rebooking, or power generation, are determined. Use of bare tethers for Radiation Belt Remediation and generation of electron beams for ionospheric research is considered. Teiher heating, arcing, and bowing or breaking, as well deployment strategies are discussed.

  3. Ion acceleration in underdense plasmas by ultra-short laser pulses

    Lifschitz, A.; Sylla, Francois; Kahaly, S.; Flacco, A.; Sánchez Arriaga, Gonzalo; Veltcheva, M.; Lefebvre, E.; Malka, V.
    We report on the ion acceleration mechanisms that occur during the interaction of an intense and ultrashort laser pulse ( λ > μ I 2 1018 W cm−2 m2) with an underdense helium plasma produced from an ionized gas jet target. In this unexplored regime, where the laser pulse duration is comparable to the inverse of the electron plasma frequency ωpe, reproducible non-thermal ion bunches have been measured in the radial direction. The two He ion charge states present energy distributions with cutoff energies between 150 and 200 keV, and a striking energy gap around 50 keV appearing consistently for all...

  4. Conductivity variations of multi-walled carbon nanotubes oriented in liquid crystal cells

    García García, Amanda; Quintana Arregui, Patxi Xabier; Bennis, Noureddine; Poudereux Sánchez, David; Otón Sánchez, José Manuel
    The control of carbon nanotubes conductivity is generating interest in several fields since it may be relevant for a number of applications. The self-organizing properties of liquid crystals may be used to impose alignment on dispersed carbon nanotubes,thus control-ling their conductivity and its anisotropy. This leads to a number of possible applications in photonic and electronic devices such as electrically controlled carbon nanotube switch- es and crossboards. In this work, cells of liquid crystals doped with multi-walled nanotubes have been prepared in different configurations. Their conductivity variations upon switching have been investigated. It turns out that conductivity evolution depends on the initial configuration...

  5. Tunable liquid crystal-photonic crystal fiber interferometer

    Poudereux Sánchez, David; Corredera Guillén, Pedro; Otón Martínez, Eva; Otón Sánchez, José Manuel; Quintana Arregui, Patxi Xabier
    In this work, we present a novel interferometer based on liquid crystal and photonic crystal fiber technology. The objective of this project is the development of a tunable (switchable) modal (Mach-Zehnder) interferometer for optical communications or sensing.

  6. Wedged analog tunable beam steering device based on cholesteric liquid crystals

    Otón Martínez, Eva; Piecek, Wiktor; Morawiak, Przemyslaw; Geday, Morten Andreas; Otón Sánchez, José Manuel
    In this work we propose a novel cholesteric liquid crystal beam steering device based on the Kerr effect. The first version of the device consists of two ITO coated glass plates, with intentionally prepared electrodes, assembled together with a thickness gradient between both sides of the device. One side of the cell has two substrates at direct contact; the other side has separated substrates to form the wedge. The cell was filled with a cholesteric liquid crystal. The liquid crystal material is an innovative mixture called 1892E with extremely low viscosity doped with a ZLI chiral nematogen. The proposed beam...

  7. Orthoconic antiferroelectric liquid crystals for non-display applications

    Bennis, Noureddine; García García, Amanda; Dabrowski, R.; Czerwinski, Michal; Geday, Morten Andreas
    Antiferroelectric liquid crystals are attractive for microdisplay applications, because of their fast switching and wide viewing angle; however the pretransitional effect reduces the contrast of the display. As a promising alternative orthoconic antiferroelectric liquid crystals (OAFLC) with a cone angle of 90º provide a good dark state between crossed polarized independently of the cell rotation. These materials are properly surface stabilized in 1.5μm thick cell required for π retardation, which limits their use in display applications. In this work, new OAFLC mixtures have been surface stabilized in thick cells. This achievement may open a new area of OAFLC applications in...

  8. Effect of strain and magnetic field on the critical current and electric resistance of the joints between HTS coated conductors

    Konstantopoulou, Konstantina; Serazin, M.; Lloberas, J.; Granados, X.; Sanmarti, M.; Obradors, X.; Pastor Caño, Jose Ignacio
    Engineering of devices and systems such as magnets, fault current limiters or cables, based on High Temperature Superconducting wires requires a deep characterization of the possible degradation of their properties by handling at room temperature as well as during the service life thus establishing the limits for building up functional devices and systems. In the present work we report our study regarding the mechanical behavior of spliced joints between commercial HTS coated conductors based on YBCO at room temperature and service temperature, 77 K. Tensile tests under axial stress and the evolution of the critical current and the electric resistance of the joints have been measured. The complete...

  9. Effect of strain and magnetic field on the critical current and electric resistance of the joints between HTS coated conductors

    Konstantopoulou, Konstantina; Serazin, M.; Lloberas, J.; Granados, X.; Sanmarti, M.; Obradors, X.; Pastor Caño, Jose Ignacio
    Engineering of devices and systems such as magnets, fault current limiters or cables, based on High Temperature Superconducting wires requires a deep characterization of the possible degradation of their properties by handling at room temperature as well as during the service life thus establishing the limits for building up functional devices and systems. In the present work we report our study regarding the mechanical behavior of spliced joints between commercial HTS coated conductors based on YBCO at room temperature and service temperature, 77 K. Tensile tests under axial stress and the evolution of the critical current and the electric resistance of the joints have been measured. The complete...

  10. Electromagnetic interaction between a laser beam and semiconductor nanowires deposited on different substrates: Raman enhancement in Si Nanowires

    Anaya, J.; Jiménez, Juan; Rodríguez Domínguez, Andrés; Rodríguez Rodríguez, Tomás
    Raman scattering of Si nanowires (NWs) presents antenna effects. The electromagnetic resonance depends on the electromagnetic coupling of the system laser/NW/substrate. The antenna effect of the Raman signal was measured in individual NWs deposited on different substrates, and also free standing NWs in air. The one phonon Raman band in NWs can reach high intensities depending on the system configuration; values of Raman intensity per unit volume more than a few hundred times with respect to bulk substrate can be obtainedRaman scattering of Si nanowires (NWs) presents antenna effects. The electromagnetic resonance depends on the electromagnetic coupling of the system...

  11. Bifurcation diagrams for polymer blends with diffuse interfaces in confined and adaptive geometries

    Madruga Sánchez, Santiago; Bribesh, Fathi; Thiele, Uwe
    Dynamics of binary mixtures such as polymer blends, and fluids near the critical point, is described by the model-H, which couples momentum transport and diffusion of the components [1]. We present an extended version of the model-H that allows to study the combined effect of phase separation in a polymer blend and surface structuring of the film itself [2]. We apply it to analyze the stability of vertically stratified base states on extended films of polymer blends and show that convective transport leads to new mechanisms of instability as compared to the simpler diffusive case described by the Cahn- Hilliard...

  12. Wide-angle, high-concentration photovoltaics to compete with flat plate systems

    Mohedano, Rubén; Cvetkovic, Aleksandra; Benitez Gimenez, Pablo; Miñano Dominguez, Juan Carlos; Hernández Sanz, Maikel; Zamora Herranz, Pablo; Vilaplana, J.
    A novel photovoltaic concentrator enables highly uniform irradiance on a small number of efficient solar cells. The maximum electrical power of a photovoltaic (PV) energy installation depends on three factors: the available irradiance, the size of the systems collecting sunlight, and the rate at which the device transforms light into electricity (the conversion efficiency). Developers can maximize the irradiance by carefully selecting the site and orientation of the solar facility. But they can only expand their sunlight collection systems for standard flat plate PV devices by increasing the number of solar cells, at greater cost. Here, we consider the advantages...

  13. Física del botafumeiro

    Sanmartín Losada, Juan Ramón
    Hace siete siglos se instaló un mecanismo destinado al culto en la catedral de Santiago de Compostela, que introduce efectos dinámicos refinados. Pudo haber originado las primeras experiencias sobre caos determinista.

  14. Survivability analysis of tape-tether against multiple impact with tiny debris

    García-Pelayo Novo, Ricardo Ángel; Khan, Shaker Bayajid; Sanmartín Losada, Juan Ramón
    We show that for a tether at 800 km altitude, which is 5 km long, 2 cm wide and 0.05 mm thick, the risk of substantial damage during a 3 month period due to multiple impacts with debris or micrometeoroids is low, of about 1.4%. By substantial damage we mean that if the tape is divided in 2 cm2 cm squares, then in some square the damaged area by bombardment with debris or micrometeoroids exceeds 11% of the area of the square. Furthermore, we show that the danger posed by the micrometeoroids is negligible compared to the risk posed by the debris.

  15. Propellantless de orbiting of space debris by bare electrodynamic tethers

    Sanmartín Losada, Juan Ramón

  16. Floating Bare Tether as Upper Atmosphere Probe

    Sanmartín Losada, Juan Ramón; Charro, Mario; Peláez, J.; Tinao, I.; Elaskar, Sergio; Hilgers, A.
    Use of a (bare) conductive tape electrically floating in LEO as an effective e-beam source that produces artificial auroras, and is free of problems that have marred standard beams, is considered. Ambient ions impacting the tape with KeV energies over most of its length liberate secondary electrons, which race down the magnetic field and excite neutrals in the E-layer, resulting in auroral emissions. The tether would operate at night-time with both a power supply and a plasma contactor off; power and contactor would be on at daytime for reboost. The optimal tape thickness yielding a minimum mass for an autonomous...

  17. A proposed bare-tether experiment on board a sounding rocket

    Fuji, H.A.; Takegahara, H.; Oyama, K.; Sasaki, S.; Yamagiwa, Y.; Kruijff, M.; Heide, E.J. Van der; Sanmartín Losada, Juan Ramón; Charro, Mario
    A mission on board a sounding rocket to carry out two bare-tether experiments is proposed: a test of orbital-motion-limited (OML) collection and the proof-of-flight of a technique to determine the (neutral) density vertical profile in the critical E-layer. Since full bias from the motional field will be small (~ 20V), corresponding to a tape 1 km long and V rocket <8 km/s, a power source with a range of supply voltages of few kV would be used. First, the negative terminal of the supply would be connected to the tape, and the positive terminal to a round, conductive boom of...

  18. ‘State-of-the-art’ of building integrated photovoltaic products

    Cerón, Isabel; Caamaño Martín, Estefanía; Neila Gonzalez, Francisco Javier
    During the last decades, the photovoltaic (PV) modules and their associated architectural materials are increasingly being incorporated into the construction of the building envelope such as façade, roof and skylights in the urban centers. This paper analyzes the-state-of-the-art of the PV elements and construction materials which are advertised as BIPV-products at the most important companies in the world. For this purpose 136 companies and 445 PV elements have been investigated and analyzed from a technical and architectural point of view. Also, the study has been divided into two main groups according to industry which producing the product: BIPV-Modules, which comes from...

  19. Bare-tether cathodic contact through thermionic emission by low-W materials

    Chen, Xin; Sanmartín Losada, Juan Ramón

  20. Electrodynamic tether for scientific mission in low Jovian orbit

    Sanmartín Losada, Juan Ramón; Bombardelli, Claudio; Charro, Mario; Lorenzini, Enrico C.
    An electrodynamic bare tether is shown to allow carrying out scientific observations very close to Jupiter, for exploration of its surface and subsurface, and ionospheric and atmospheric in-situ measurements. Starting at a circular equatorial orbit of radius about 1.3/1.4 times the Jovian radius, continuous propellantless Lorentz drag on a thin-tape tether in the 1-5 km length range would make a spacecraft many times as heavy as the tape slowly spiral in, over a period of many months, while generating power at a load plugged in the tether circuit for powering instruments in science data acquisition and transmission. Lying under the Jovian...

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