1,043 research outputs found
Effects of Interplanetary Dust on the LISA drag-free Constellation
The analysis of non-radiative sources of static or time-dependent
gravitational fields in the Solar System is crucial to accurately estimate the
free-fall orbits of the LISA space mission. In particular, we take into account
the gravitational effects of Interplanetary Dust (ID) on the spacecraft
trajectories. The perturbing gravitational field has been calculated for some
ID density distributions that fit the observed zodiacal light. Then we
integrated the Gauss planetary equations to get the deviations from the LISA
keplerian orbits around the Sun. This analysis can be eventually extended to
Local Dark Matter (LDM), as gravitational fields are expected to be similar for
ID and LDM distributions. Under some strong assumptions on the displacement
noise at very low frequency, the Doppler data collected during the whole LISA
mission could provide upper limits on ID and LDM densities.Comment: 11 pages, 6 figures, to be published on the special issue of
"Celestial Mechanics and Dynamical Astronomy" on the CELMEC V conferenc
Recommended from our members
Real time visualization and analysis of sensory hair arrays using fast image processing and proper orthogonal decomposition
This paper presents an approach both to receiving multiple sensor data from a flow in real time and to analyzing these data in order to characterize the flow condition and, if necessary, control the flow. In order to obtain the data, an optical micro-pillar array acting as distributed wall-shear sensor was developed and interrogated optically with an LDM (long distance microscope). Together, the micro-pillar array and the LDM form a channeling optics, which allows magnified imaging of larger numbers of individual pillars simultaneously. The sensor was tested in a turbulent wall shear stress field under varying conditions (Reynolds number). A frame rate of 3000 fps was used since the higher the temporal resolution is, the more specific flow control strategies might be applied later in realistic application. However, the temporal high resolution would lead to a vast amount of data, which is difficult to analyze in real time. Therefore, a fast image processing algorithm is developed, which detects the tip deflections of the pillars and vectorizes the wall-shear stress field online. The extracted data fields are then broken down into equidistant and overlapping windows in order to guarantee fast POD (proper orthogonal decomposition) modes calculation. The POD is applied to each of these windows and the extracted modes are compared, summarized and collected in a library. Finally, this library is again applied to the flow but under different conditions in order to identify the state of the current flow in real time
Dark Matter investigation by DAMA at Gran Sasso
Experimental observations and theoretical arguments at Galaxy and larger
scales have suggested that a large fraction of the Universe is composed by Dark
Matter particles. This has motivated the DAMA experimental efforts to
investigate the presence of such particles in the galactic halo by exploiting a
model independent signature and very highly radiopure set-ups deep underground.
Few introductory arguments are summarized before presenting a review of the
present model independent positive results obtained by the DAMA/NaI and
DAMA/LIBRA set-ups at the Gran Sasso National Laboratory of the INFN.
Implications and model dependent comparisons with other different kinds of
results will be shortly addressed. Some arguments put forward in literature
will be confuted.Comment: review article, 71 pages, 25 figures, 8 tables; v2: minor
modifications. In publication on the International Journal of Modern Physics
Dark matter annihilation and non-thermal Sunyaev-Zel'dovich effect: II. dwarf spheroidal galaxy
We calculate the CMB temperature distortion due to the energetic electrons
and positrons produced by dark matter annihilation (Sunyaev-Zel'dovich effect),
in dwarf spheroidal galaxies (dSphs). In the calculation we have included two
important effects which were previously ignored. First we show that the
electron-positron pairs with energy less than GeV, which were neglected in
previous calculation, could contribute a significant fraction of the total
signal. Secondly we also consider the full effects of diffusion loss, which
could significantly reduce the density of electron-positron pairs at the center
of cuspy halos. For neutralinos, we confirm that detecting such kind of SZ
effect is beyond the capability of the current or even the next generation
experiments. In the case of light dark matter (LDM) the signal is much larger,
but even in this case it is only marginally detectable with the next generation
of experiment such as ALMA. We conclude that similar to the case of galaxy
clusters, in the dwarf galaxies the SZ_2DM} effect is not a strong probe of
DM annihilations.Comment: 22 pages, 9 figures, version accepted by JCA
Advanced Layered Divsion Multiplexing Technologies for Next-Gen Broadcast
Tesis por compendioDesde comienzos del siglo XXI, los sistemas de radiodifusión terrestre han sido culpados de un uso ineficiente del espectro asignado. Para aumentar la eficiencia espectral, los organismos de estandarización de TV digital comenzaron a desarrollar la evolución técnica de los sistemas de TDT de primera generación. Entre otros, uno de los objetivos principales de los sistemas de TDT de próxima generación (DVB-T2 y ATSC 3.0) es proporcionar simultáneamente servicios de TV a dispositivos móviles y fijos. El principal inconveniente de esta entrega simultánea son los diferentes requisitos de cada condición de recepción. Para abordar estas limitaciones, se han considerado diferentes técnicas de multiplexación. Mientras que DVB-T2 acomete la entrega simultánea de los dos servicios mediante TDM, ATSC 3.0 adoptó la Multiplexación por División en Capas (LDM). LDM puede superar a TDM y a FDM al aprovechar la relación de Protección de Error Desigual (UEP), ya que ambos servicios, llamados capas, utilizan todos los recursos de frecuencia y tiempo con diferentes niveles de potencia. En el lado del receptor, se distinguen dos implementaciones, de acuerdo con la capa a decodificar. Los receptores móviles solo están destinados a obtener la capa superior, conocida como Core Layer (CL). Para no aumentar su complejidad en comparación con los receptores de capa única, la capa inferior, conocida como Enhanced Layer (EL), es tratada como un ruido adicional en la decodificación. Los receptores fijos aumentan su complejidad, ya que deben realizar un proceso de Cancelación de Interferencia (SIC) sobre la CL para obtener la EL. Para limitar la complejidad adicional de los receptores fijos, las capas de LDM en ATSC 3.0 están configuradas con diferentes capacidades de corrección, pero comparten el resto de bloques de la capa fÃsica, incluido el TIL, el PP, el tamaño de FFT, y el GI.
Esta disertación investiga tecnologÃas avanzadas para optimizar el rendimiento de LDM. Primero se propone una optimización del proceso de demapeo para las dos capas de LDM. El algoritmo propuesto logra un aumento de capacidad, al tener en cuenta la forma de la EL en el proceso de demapeo de la CL. Sin embargo, el número de distancias Euclidianas a computar puede aumentar
significativamente, conduciendo no solo a receptores fijos más complejos, sino también a receptores móviles más complejos. A continuación, se determina la configuración de piloto ATSC 3.0 más adecuada para LDM. Teniendo en cuenta que las dos capas comparten el mismo PP, surge una contrapartida entre la densidad de pilotos (CL) y la redundancia sobre los datos (EL). A partir de los resultados de rendimiento, se recomienda el uso de un PP no muy denso, ya que ya han sido diseñados para hacer frente a ecos largos y altas velocidades. La amplitud piloto óptima depende del estimador de canal en los receptores (ej., se recomienda la amplitud mÃnima para una implementación Wiener, mientras que la máxima para una implementación FFT).
También se investiga la potencial transmisión conjunta de LDM con tres tecnologÃas avanzadas adoptadas en ATSC 3.0: las tecnologÃas de agregación MultiRF, los esquemas de MISO distribuido y los de MIMO colocalizado. Se estudian los potenciales casos de uso, los aspectos de implementación del transmisor y el receptor, y las ganancias de rendimiento de las configuraciones conjuntas para las dos capas de LDM. Las restricciones adicionales de combinar LDM con las tecnologÃas avanzadas se consideran admisibles, ya que las mayores demandas ya están contempladas en ATSC 3.0 (ej., una segunda cadena de recepción). Se obtienen ganancias significativas en condiciones de recepción peatonal gracias a la diversidad en frecuencia proporcionada por las tecnologÃas MultiRF. La conjunción de LDM con esquemas de MISO proporciona ganancias de rendimiento significativas en redes SFN para la capa fija con el esquema de Alamouti.Since the beginning of the 21st century, terrestrial broadcasting systems have been blamed of an inefficient use of the allocated spectrum. To increase the spectral efficiency, digital television Standards Developing Organizations settled to develop the technical evolution of the first-generation DTT systems. Among others, a primary goal of next-generation DTT systems (DVB-T2 and ATSC 3.0) is to simultaneously provide TV services to mobile and fixed devices. The major drawback of this simultaneous delivery is the different requirement of each reception condition. To address these constraints different multiplexing techniques have been considered. While DVB-T2 fulfilled the simultaneous delivery of the two services by TDM, ATSC 3.0 adopted the LDM technology. LDM can outperform TDM and FDM by taking advantage of the UEP ratio, as both services, namely layers, utilize all the frequency and time resources with different power levels. At receiver side, two implementations are distinguished, according to the intended layer. Mobile receivers are only intended to obtain the upper layer, known as CL. In order not to increase their complexity compared to single layer receivers, the lower layer, known as EL is treated as an additional noise on the CL decoding. Fixed receivers, increase their complexity, as they should performed a SIC process on the CL for getting the EL. To limit the additional complexity of fixed receivers, the LDM layers in ATSC 3.0 are configured with different error correction capabilities, but share the rest of physical layer parameters, including the TIL, the PP, the FFT size, and the GI.
This dissertation investigates advanced technologies to optimize the LDM performance. A demapping optimization for the two LDM layers is first proposed. A capacity increase is achieved by the proposed algorithm, which takes into account the underlying layer shape in the demapping process. Nevertheless, the number of Euclidean distances to be computed can be significantly increased, contributing to not only more complex fixed receivers, but also more complex mobile receivers. Next, the most suitable ATSC 3.0 pilot configuration for LDM is determined. Considering the two layers share the same PP a trade-off between pilot density (CL) and data overhead (EL) arises. From the performance results, it is recommended the use of a not very dense PP, as they have been already designed to cope with long echoes and high speeds. The optimum pilot amplitude depends on the channel estimator at receivers (e.g. the minimum amplitude is recommended for a Wiener implementation, while the maximum for a FFT implementation).
The potential combination of LDM with three advanced technologies that have been adopted in ATSC 3.0 is also investigated: MultiRF technologies, distributed MISO schemes, and co-located MIMO schemes. The potential use cases, the transmitter and receiver implementations, and the performance gains of the joint configurations are studied for the two LDM layers. The additional constraints of combining LDM with the advanced technologies is considered admissible, as the greatest demands (e.g. a second receiving chain) are already contemplated in ATSC 3.0. Significant gains are found for the mobile layer at pedestrian reception conditions thanks to the frequency diversity provided by MultiRF technologies. The conjunction of LDM with distributed MISO schemes provides significant performance gains on SFNs for the fixed layer with Alamouti scheme. Last, considering the complexity in the mobile receivers and the CL performance, the recommended joint configuration is MISO in the CL and MIMO in the EL.Des de començaments del segle XXI, els sistemes de radiodifusió terrestre han sigut culpats d'un ús ineficient de l'espectre assignat. Per a augmentar l'eficiència espectral, els organismes d'estandardització de TV digital van començar a desenvolupar l'evolució tècnica dels sistemes de TDT de primera generació. Entre altres, un dels objectius principals dels sistemes de TDT de pròxima generació (DVB-T2 i el ATSC 3.0) és proporcionar simultà niament serveis de TV a dispositius mòbils i fixos. El principal inconvenient d'aquest lliurament simultani són els diferents requisits de cada condició de recepció. Per a abordar aquestes limitacions, s'han considerat diferents tècniques de multiplexació. Mentre que DVB-T2 escomet el lliurament simultani dels dos serveis mitjançant TDM, ATSC 3.0 va adoptar la Multiplexació per Divisió en Capes (LDM). LDM pot superar a TDM i a FDM en aprofitar la relació de Protecció d'Error Desigual (UEP), ja que tots dos serveis, cridats capes, utilitzen tots els recursos de freqüència i temps amb diferents nivells de potència. En el costat del receptor, es distingeixen dues implementacions, d'acord amb la capa a decodificar. Els receptors mòbils solament estan destinats a obtenir la capa superior, coneguda com Core Layer (CL). Per a no augmentar la seua complexitat en comparació amb els receptors de capa única, la capa inferior, coneguda com Enhanced Layer (EL), és tractada com un soroll addicional en la decodificació. Els receptors fixos augmenten la seua complexitat, ja que han de realitzar un procés de Cancel·lació d'Interferència (SIC) sobre la CL per a obtenir l'EL. Per a limitar la complexitat addicional dels receptors fixos, les capes de LDM en ATSC 3.0 estan configurades amb diferents capacitats de correcció, però comparteixen la resta de blocs de la capa fÃsica, inclòs el TIL, el PP, la grandà ria de FFT i el GI.
Aquesta dissertació investiga tecnologies avançades per a optimitzar el rendiment de LDM. Primer es proposa una optimització del procés de demapeo per a les dues capes de LDM. L'algoritme proposat aconsegueix un augment de capacitat, en tenir en compte la forma de l'EL en el procés de demapeo de la CL. No obstant açò, el nombre de distà ncies Euclidianes a computar pot augmentar significativament, conduint NO sols a receptors fixos més complexos, sinó també a receptors mòbils més complexos. A continuació, es determina la configuració de pilot ATSC 3.0 més adequada per a LDM. Tenint en compte que les dues capes comparteixen el mateix PP, es produeix una contrapartida entre la densitat de pilots (CL) i la redundà ncia sobre les dades (EL). A partir dels resultats de rendiment, es recomana l'ús d'un PP no gaire dens, ja que ja han sigut dissenyats per a fer front a ecos llargs i altes velocitats. L'amplitud pilot òptima depèn de l'estimador de canal en els receptors (ex., es recomana l'amplitud mÃnima per a una implementació Wiener, mentre que la mà xima per a una implementació FFT).
També s'investiga la potencial transmissió conjunta de LDM amb tres tecnologies avançades adoptades en ATSC 3.0: les tecnologies d'agregació de MultiRF, els esquemes de MISO distribuït i els de MIMO colocalitzat. S'estudien els potencials casos d'ús, els principals aspectes d'implementació del transmissor i el receptor, i els guanys de rendiment de les configuracions conjuntes per a les dues capes de LDM. Les restriccions addicionals de combinar LDM amb les tecnologies avançades es consideren admissibles, ja que les majors demandes ja estan contemplades en ATSC 3.0 (ex., una segona cadena de recepció). S'obtenen guanys significatius per a la capa mòbil en condicions de recepció per als vianants grà cies a la diversitat en freqüència proporcionada per les tecnologies MultiRF. La conjunció de LDM amb esquemes MISO distribuïts proporciona guanys de rendiment significatius en xarxes SFN per a la capa fixa amb l'esquema d'Alamouti.Garro Crevillén, E. (2018). Advanced Layered Divsion Multiplexing Technologies for Next-Gen Broadcast [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/105559TESISCompendi
Content delivery over multi-antenna wireless networks
The past few decades have witnessed unprecedented advances in information technology, which have significantly shaped the way we acquire and process information in our daily lives. Wireless communications has become the main means of access to data through mobile devices, resulting in a continuous exponential growth in wireless data traffic, mainly driven by the demand for high quality content.
Various technologies have been proposed by researchers to tackle this growth in 5G and beyond, including the use of increasing number of antenna elements, integrated point-to-multipoint delivery and caching, which constitute the core of this thesis. In particular, we study non-orthogonal content delivery in multiuser multiple-input-single-output (MISO) systems. First, a joint beamforming strategy for simultaneous delivery of broadcast and unicast services is investigated, based on layered division multiplexing (LDM) as a means of superposition coding. The system performance in terms of minimum required power under prescribed quality-of-service (QoS) requirements is examined in comparison with time division multiplexing (TDM). It is demonstrated through simulations that the non-orthogonal delivery strategy based on LDM significantly outperforms the orthogonal strategy based on TDM in terms of system throughput and reliability. To facilitate efficient implementation of the LDM-based beamforming design, we further propose a dual decomposition-based distributed approach. Next, we study an efficient multicast beamforming design in cache-aided multiuser MISO systems, exploiting proactive content placement and coded delivery. It is observed that the complexity of this problem grows exponentially with the number of subfiles delivered to each user in each time slot, which itself grows exponentially with the number of users in the system. Therefore, we propose a low-complexity alternative through time-sharing that limits the number of subfiles that can be received by a user in each time slot. Moreover, a joint design of content delivery and multicast beamforming is proposed to further enhance the system performance, under the constraint on maximum number of subfiles each user can decode in each time slot. Finally, conclusions are drawn in Chapter 5, followed by an outlook for future works.Open Acces
Solutions for New Terrestrial Broadcasting Systems Offering Simultaneously Stationary and Mobile Services
221 p.[EN]Since the first broadcasted TV signal was transmitted in the early decades of
the past century, the television broadcasting industry has experienced a series of
dramatic changes. Most recently, following the evolution from analogue to digital
systems, the digital dividend has become one of the main concerns of the
broadcasting industry. In fact, there are many international spectrum authorities
reclaiming part of the broadcasting spectrum to satisfy the growing demand of
other services, such as broadband wireless services, arguing that the TV services
are not very spectrum-efficient.
Apart from that, it must be taken into account that, even if up to now the
mobile broadcasting has not been considered a major requirement, this will
probably change in the near future. In fact, it is expected that the global mobile
data traffic will increase 11-fold between 2014 and 2018, and what is more, over
two thirds of the data traffic will be video stream by the end of that period.
Therefore, the capability to receive HD services anywhere with a mobile device is
going to be a mandatory requirement for any new generation broadcasting system.
The main objective of this work is to present several technical solutions that
answer to these challenges. In particular, the main questions to be solved are the
spectrum efficiency issue and the increasing user expectations of receiving high
quality mobile services. In other words, the main objective is to provide technical
solutions for an efficient and flexible usage of the terrestrial broadcasting spectrum
for both stationary and mobile services.
The first contributions of this scientific work are closely related to the study of
the mobile broadcast reception. Firstly, a comprehensive mathematical analysis of
the OFDM signal behaviour over time-varying channels is presented. In order to
maximize the channel capacity in mobile environments, channel estimation and
equalization are studied in depth. First, the most implemented equalization
solutions in time-varying scenarios are analyzed, and then, based on these existing
techniques, a new equalization algorithm is proposed for enhancing the receivers’
performance.
An alternative solution for improving the efficiency under mobile channel
conditions is treating the Inter Carrier Interference as another noise source.
Specifically, after analyzing the ICI impact and the existing solutions for reducing
the ICI penalty, a new approach based on the robustness of FEC codes is
presented. This new approach employs one dimensional algorithms at the receiver
and entrusts the ICI removing task to the robust forward error correction codes.
Finally, another major contribution of this work is the presentation of the
Layer Division Multiplexing (LDM) as a spectrum-efficient and flexible solution
for offering stationary and mobile services simultaneously. The comprehensive
theoretical study developed here verifies the improved spectrum efficiency,
whereas the included practical validation confirms the feasibility of the system and
presents it as a very promising multiplexing technique, which will surely be a strong
candidate for the next generation broadcasting services.[ES]Desde el comienzo de la transmisión de las primeras señales de televisión a
principios del siglo pasado, la radiodifusión digital ha evolucionado gracias a una
serie de cambios relevantes. Recientemente, como consecuencia directa de la
digitalización del servicio, el dividendo digital se ha convertido en uno de los
caballos de batalla de la industria de la radiodifusión. De hecho, no son pocos los
consorcios internacionales que abogan por asignar parte del espectro de
radiodifusión a otros servicios como, por ejemplo, la telefonÃa móvil, argumentado
la poca eficiencia espectral de la tecnologÃa de radiodifusión actual.
Asimismo, se debe tener en cuenta que a pesar de que los servicios móviles no
se han considerado fundamentales en el pasado, esta tendencia probablemente
variará en el futuro cercano. De hecho, se espera que el tráfico derivado de
servicios móviles se multiplique por once entre los años 2014 y 2018; y lo que es
más importante, se pronostica que dos tercios del tráfico móvil sea video streaming
para finales de ese periodo. Por lo tanto, la posibilidad de ofrecer servicios de alta
definición en dispositivos móviles es un requisito fundamental para los sistemas de
radiodifusión de nueva generación.
El principal objetivo de este trabajo es presentar soluciones técnicas que den
respuesta a los retos planteados anteriormente. En particular, las principales
cuestiones a resolver son la ineficiencia espectral y el incremento de usuarios que
demandan mayor calidad en los contenidos para dispositivos móviles. En pocas
palabras, el principal objetivo de este trabajo se basa en ofrecer una solución más
eficiente y flexible para la transmisión simultánea de servicios fijos y móviles.
La primera contribución relevante de este trabajo está relacionada con la
recepción de la señal de televisión en movimiento. En primer lugar, se presenta un
completo análisis matemático del comportamiento de la señal OFDM en canales
variantes con el tiempo. A continuación, con la intención de maximizar la
capacidad del canal, se estudian en profundidad los algoritmos de estimación y
ecualización. Posteriormente, se analizan los algoritmos de ecualización más
implementados, y por último, basándose en estas técnicas, se propone un nuevo
algoritmo de ecualización para aumentar el rendimiento de los receptores en tales
condiciones.
Del mismo modo, se plantea un nuevo enfoque para mejorar la eficiencia de
los servicios móviles basado en tratar la interferencia entre portadoras como una
fuente de ruido. Concretamente, tras analizar el impacto del ICI en los receptores
actuales, se sugiere delegar el trabajo de corrección de dichas distorsiones en
códigos FEC muy robustos.
Finalmente, la última contribución importante de este trabajo es la
presentación de la tecnologÃa LDM como una manera más eficiente y flexible para
la transmisión simultánea de servicios fijos y móviles. El análisis teórico presentado
confirma el incremento en la eficiencia espectral, mientras que el estudio práctico
valida la posible implementación del sistema y presenta la tecnologÃa LDM c
Investigating the mechanotransduction by two-photon fluorescence microscopy measurement of intracellular free energy of binding
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008.Includes bibliographical references (p. 99-108).Force, due either to haemodynamic shear stress or relayed directly to the cell through adhesion complexes, is transmitted and translated into biological signals. This process is known as mechanotransduction. Extensive studies have been carried out on the signaling pathways involved in mechanotransduction. However, the mechanism(s) of mechanotransduction has yet to be fully understood. This thesis focuses on the measurement of the intracellular binding constant between focal adhesion proteins of interest, GFP-Paxillin and FAT-mCherry, using two-photon excitation fluorescence microscopy and the utility of it as a measure of protein conformational change. The hypothesis tested is that force-induced changes in protein conformation alter inter-protein binding affinity. A comprehensive toolkit that utilizes fluorescence microscopy techniques, Forster Resonance Energy Transfer (FRET) and its corollary, Fluorescence Lifetime Imaging (FLIM), as well as Fluorescence Correlation Spectroscopy (FCS), was developed. A procedure by which low photon counts cell data from FLIM could be included in global analysis fits and be corrected for was developed. This results in the recovery of maximum information from cellular data. Successful intracellular FCS measurements were combined with FLIM global analysis data to calculate the free energy of binding between GFP-Paxillin and FAT-mCherry. Results demonstrate that inter-cell heterogeneity exists and likely gives rise to differences in measured AIG. The application of these measurement techniques to cells experiencing 10% step strain shows that inter-protein binding is tighter upon stretch application. The source of this change is not clear, though Tyr phosphorylation has been ruled out by biochemical disruption of kinase activity.by Nur Aida Abdul Rahim.Ph.D
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