Capacity Enhancement Using MIMO Antenna Arrays in Realistic Macro-Cellular Urban Environment

In MIMO systems the antenna array configuration in the BS and MS has a large influence on the available channel capacity. In this paper, we first introduce a new Frequency Selective (FS) MIMO framework for macro-cells in a realistic urban environment. The MIMO channel is built over a previously developed directional channel model, which considers the terrain and clutter information in the cluster, line-of-sight and link loss calculations. Next, MIMO configuration characteristics are investigated in order to maximize capacity, mainly the number of antennas, inter-antenna spacing and SNR impact. Channel and capacity simulation results are presented for the city of Lisbon, Portugal, using different antenna configurations. Two power allocations schemes are considered, uniform distribution and FS spatial water-filling. The results suggest optimized MIMO configurations, considering the antenna array size limitations, specially at the MS side.

On the Suitability of Suffix Arrays for Lempel-Ziv Data Compression

Lossless compression algorithms of the Lempel-Ziv (LZ) family are widely used nowadays. Regarding time and memory requirements, LZ encoding is much more demanding than decoding. In order to speed up the encoding process, efficient data structures, like suffix trees, have been used. In this paper, we explore the use of suffix arrays to hold the dictionary of the LZ encoder, and propose an algorithm to search over it. We show that the resulting encoder attains roughly the same compression ratios as those based on suffix trees. However, the amount of memory required by the suffix array is fixed, and much lower than the variable amount of memory used by encoders based on suffix trees (which depends on the text to encode). We conclude that suffix arrays, when compared to suffix trees in terms of the trade-off among time, memory, and compression ratio, may be preferable in scenarios (e.g., embedded systems) where memory is at a premium and high speed is not critical.

Conceito de volume

Este estudo analisa o modo como se desenvolve a aprendizagem do conceito de volume nos alunos do 6º ano de escolaridade, no quadro de uma proposta pedagógica que dá ênfase a actividades que apelam à visualização e ao raciocínio espacial. O seu objectivo principal foi o de compreender as ideias que os alunos do 6.º ano têm sobre volume e perceber como se desenvolvem quando são envolvidos numa experiência de ensino, tendo por base uma cadeia de tarefas que apelam à visualização e ao raciocínio espacial. O estudo seguiu uma metodologia de investigação qualitativa baseada em estudos de caso. A proposta pedagógica foi desenvolvida em quatro aulas; três de noventa minutos e uma de quarenta e cinco minutos, durante os 2º e 3º períodos do ano lectivo de 2009/2010. A recolha de dados envolveu a realização de gravações áudio, em ambiente de sala de aula, dos alunos que constituíram os estudos de caso, registo de observações do desempenho dos alunos e os documentos produzidos por estes. Os resultados mostram que, ao longo da proposta pedagógica, os alunos adquiriram estratégias de contagem que lhes permitiram criar estruturas, para compreender a organização dos paralelepípedos e desenvolver o conceito de volume. iii ABSTRACT This study examines how 6th graders’ students develop the concept of volume in a learning experience context which emphasizes the visualization and spatial reasoning. The main objective of this study is to understand the ideas of 6th grade students about volume and see how they develop them when they are involved in a learning experience, based on a sequence of tasks that call for visualization and spatial reasoning. The study followed a qualitative research methodology based on case studies. The learning experience was developed in four classes, three ninety minutes period and one forty-five minutes, during the 2nd and 3rd terms of the school year 2009/2010. Data collection involved the use of audio recordings in the classroom environment, recording observations of student performance and the documents produced by them. The results showed that, over the learning experience, students acquired counting strategies that allowed them to create structures for understanding the organization of cubes arrays and develop the concept of volume.

New p-i-n Si : H imager configuration for spatial resolution improvement

Amorphous glass/ZnO-Al/p(a-Si:H)/i(a-Si:H)/n(a-Si1-xCx:H)/Al imagers with different n-layer resistivities were produced by plasma enhanced chemical vapour deposition technique (PE-CVD). An image is projected onto the sensing element and leads to spatially confined depletion regions that can be readout by scanning the photodiode with a low-power modulated laser beam. The essence of the scheme is the analog readout, and the absence of semiconductor arrays or electrode potential manipulations to transfer the information coming from the transducer. The influence of the intensity of the optical image projected onto the sensor surface is correlated with the sensor output characteristics (sensitivity, linearity blooming, resolution and signal-to-noise ratio) are analysed for different material compositions (0.5 < x < 1). The results show that the responsivity and the spatial resolution are limited by the conductivity of the doped layers. An enhancement of one order of magnitude in the image intensity signal and on the spatial resolution are achieved at 0.2 mW cm(-2) light flux by decreasing the n-layer conductivity by the same amount. A physical model supported by electrical simulation gives insight into the image-sensing technique used.

Digital radiography detectors: a technical overview

Developments in digital detector technologies have been taking place and new digital technologies are available for clinical practice. This chapter is intended to give a technical state-of-the-art overview about computed radiography (CR) and digital radiography (DR) detectors. CR systems use storage-phosphor image plates with a separate image readout process and DR technology converts X-rays into electrical charges by means of a readout process using TFT arrays. Digital detectors offer several advantages when compared to analogue detectors. The knowledge about digital detector technology for use in plain radiograph examinations is thus a fundamental topic to be acquired by radiology professionals and students. In this chapter an overview of digital radiography systems (both CR and DR) currently available for clinical practice is provided.

Ageing effects on the wettability behavior of laser textured silicon

In the present work we investigate the ageing of acid cleaned femtosecond laser textured < 100 > silicon surfaces. Changes in the surface structure and chemistry were analysed by Rutherford backscattering spectrometry (RBS) and X-ray photoelectron spectroscopy (XPS), in order to explain the variation with time of the water contact angles of the laser textured surfaces. It is shown that highly hydrophobic silicon surfaces are obtained immediately after laser texturing and cleaning with acid solutions (water contact angle >120 degrees). However these surfaces are not stable and ageing leads to a decrease of the water contact angle which reaches a value of 80 degrees. XPS analysis of the surfaces shows that the growth of the native oxide layer is most probably responsible for this behavior. (C) 2010 Elsevier B.V. All rights reserved.

Sub-micron structuring of silicon using femtosecond laser interferometry

We report the fabrication of planar sub-micron gratings in silicon with a period of 720 nm using a modified Michelson interferometer and femtosecond laser radiation. The gratings consist of alternated stripes of laser ablated and unmodified material. Ablated stripes are bordered by parallel ridges which protrude above the unmodified material. In the regions where ridges are formed, the laser radiation intensity is not sufficient to cause ablation. Nevertheless, melting and a significant temperature increase are expected, and ridges may be formed due to expansion of silicon during resolidification or silicon oxidation. These conclusions are consistent with the evolution of the stripes morphology as a function of the distance from the center of the grating. (C) 2013 Elsevier Ltd. All rights reserved.

Subunits of the chaperonin CCT are associated with Tetrahymena microtubule structures and are involved in cilia biogenesis

The cytosolic chaperonin CCT is a heterooligomeric complex of about 900 kDa that mediates the folding of cytoskeletal proteins. We observed by indirect immunofluorescence that the Tetrahymena TpCCTalpha, TpCCTdelta, TpCCTepsilon, and TpCCTeta-subunits colocalize with tubulin in cilia, basal bodies, oral apparatus, and contractile vacuole pores. TpCCT-subunits localization was affected during reciliation. These findings combined with atomic force microscopy measurements in reciliating cells indicate that these proteins play a role during cilia biogenesis related to microtubule nucleation, tubulin transport, and/or axoneme assembly. The TpCCT-subunits were also found to be associated with cortex and cytoplasmic microtubules suggesting that they can act as microtubule-associated proteins. The TpCCTdelta being the only subunit found associated with the macronuclear envelope indicates that it has functions outside of the 900 kDa complex. Tetrahymena cytoplasm contains granular/globular-structures of TpCCT-subunits in close association with microtubule arrays. Studies of reciliation and with cycloheximide suggest that these structures may be sites of translation and folding. Combined biochemical techniques revealed that reciliation affects the oligomeric state of TpCCT-subunits being tubulin preferentially associated with smaller CCT oligomeric species in early stages of reciliation. Collectively, these findings indicate that the oligomeric state of CCT-subunits reflects the translation capacity of the cell and microtubules integrity.

Implementação em hardware reconfigurável de método de separação de dados hiperespetrais

Relatório do Trabalho Final de Mestrado para obtenção do grau de Mestre em Engenharia de Electrónica e Telecomunicações

Efficient Implementation Of A Single-Precision Floating-Point Arithmetic Unit on FPGA

This paper presents a single precision floating point arithmetic unit with support for multiplication, addition, fused multiply-add, reciprocal, square-root and inverse squareroot with high-performance and low resource usage. The design uses a piecewise 2nd order polynomial approximation to implement reciprocal, square-root and inverse square-root. The unit can be configured with any number of operations and is capable to calculate any function with a throughput of one operation per cycle. The floatingpoint multiplier of the unit is also used to implement the polynomial approximation and the fused multiply-add operation. We have compared our implementation with other state-of-the-art proposals, including the Xilinx Core-Gen operators, and conclude that the approach has a high relative performance/area efficiency. © 2014 Technical University of Munich (TUM).

The impact of different power dividers used in a non-uniform planar antenna array

Wireless communications are widely used for various applications, requiring antennas with different features. Often, to achieve the desired radiation pattern, is necessary to employ antenna arrays, using non-uniform excitation on its elements. Power dividers can be used and the best known are the T-junction and the Wilkinson power divider, whose main advantage is the isolation between output ports. In this paper the impact of this isolation on the overall performance of a circularly polarized planar antenna array using non-uniform excitation is investigated. Results show a huge decrease of the array bandwidths either in terms of return loss or in polarization, without resistors. © 2014 IEEE.

Trends Of CPU, GPU and FPGA for high-performance computing

Floating-point computing with more than one TFLOP of peak performance is already a reality in recent Field-Programmable Gate Arrays (FPGA). General-Purpose Graphics Processing Units (GPGPU) and recent many-core CPUs have also taken advantage of the recent technological innovations in integrated circuit (IC) design and had also dramatically improved their peak performances. In this paper, we compare the trends of these computing architectures for high-performance computing and survey these platforms in the execution of algorithms belonging to different scientific application domains. Trends in peak performance, power consumption and sustained performances, for particular applications, show that FPGAs are increasing the gap to GPUs and many-core CPUs moving them away from high-performance computing with intensive floating-point calculations. FPGAs become competitive for custom floating-point or fixed-point representations, for smaller input sizes of certain algorithms, for combinational logic problems and parallel map-reduce problems. © 2014 Technical University of Munich (TUM).

Evidences for direct magnetic patterning via diffusive transformations using femtosecond laser interferometry

The application of femtosecond laser interferometry to direct patterning of thin-film magnetic alloys is demonstrated. The formation of stripe gratings with submicron periodicities is achieved in Fe1-xVx (x=18-34wt. %) layers, with a difference in magnetic moments up to Delta mu/mu similar to 20 between adjacent stripes but without any significant development of the topographical relief (<1% of the film thickness). The produced gratings exhibit a robust effect of their anisotropy shape on magnetization curves in the film plane. The obtained data witness ultrafast diffusive transformations associated with the process of spinodal decomposition and demonstrate an opportunity for producing magnetic nanostructures with engineered properties upon this basis.

Algoritmos de estimação da direção de chegada de sinal

Trabalho Final de Mestrado para obtenção do grau de Mestre em Engenharia de Eletrónica e Telecomunicações

A many-core co-processor for embedded parallel computing on FPGA

Single processor architectures are unable to provide the required performance of high performance embedded systems. Parallel processing based on general-purpose processors can achieve these performances with a considerable increase of required resources. However, in many cases, simplified optimized parallel cores can be used instead of general-purpose processors achieving better performance at lower resource utilization. In this paper, we propose a configurable many-core architecture to serve as a co-processor for high-performance embedded computing on Field-Programmable Gate Arrays. The architecture consists of an array of configurable simple cores with support for floating-point operations interconnected with a configurable interconnection network. For each core it is possible to configure the size of the internal memory, the supported operations and number of interfacing ports. The architecture was tested in a ZYNQ-7020 FPGA in the execution of several parallel algorithms. The results show that the proposed many-core architecture achieves better performance than that achieved with a parallel generalpurpose processor and that up to 32 floating-point cores can be implemented in a ZYNQ-7020 SoC FPGA.