Top Down Control in a Relatively Pristine Seagrass Ecosystem

The loss of large-bodied herbivores and/or top predators has been associated with large-scale changes in terrestrial, freshwater, and marine ecosystems around the world. Understanding the consequences of these declines has been hampered by a lack of studies in relatively pristine systems. To fill this gap, I investigated the dynamics of the relatively pristine seagrass ecosystem of Shark Bay, Australia. I began by examining the seagrass species distributions, stoichiometry, and patterns of nutrient limitation across the whole of Shark Bay. Large areas were N-limited, P-limited, or limited by factors other than nutrients. Phosphorus-limitation was centered in areas of restricted water exchange with the ocean. Nutrient content of seagrasses varied seasonally, but the strength of seasonal responses were species-specific. Using a cafeteria-style experiment, I found that fast-growing seagrass species, which had higher nutrient content experienced higher rates of herbivory than slow-growing species that are dominant in the bay but have low nutrient content. Although removal rates correlated well with nutrient content at a broad scale, within fast-growing species removal rates were not closely tied to N or P content. Using a combination of stable isotope analysis and animal borne video, I found that green turtles (Chelonia mydas) – one of the most abundant large-bodied herbivores in Shark Bay – appear to assimilate little energy from seagrasses at the population level. There was, however, evidence of individual specialization in turtle diets with some individuals foraging largely on seagrasses and others feeding primarily on macroalgae and gelatinous macroplankton. Finally, I used exclusion cages, to examine whether predation-sensitive habitat shifts by megagrazers (green turtles, dugongs) transmitted a behavior-mediated trophic cascade (BMTC) between sharks and seagrasses. In general, data were consistent with predictions of a behavior-mediated trophic cascade. Megaherbivore impacts on seagrasses were large only in the microhabitat where megaherbivores congregate to reduce predation risk. My study highlights the importance of large herbivores in structuring seagrass communities and, more generally, suggests that roving top predators likely are important in structuring communities - and possibly ecosystems - through non-consumptive pathways.

Analisi Sperimentale delle Prestazioni di Nodi Wireless LoRa in Presenza di Interferente

L’obiettivo dell’Internet of Things (IoT), come suggerisce il nome, è quello di connettere oggetti (spesso alimentati a batteria) alla rete Internet per poterne avere un controllo da remoto. Lo sviluppo di questa tecnologia prevede la progettazione di dispositivi che abbiano: un basso costo per unità, una durata della batteria sufficientemente lunga (anche dell’ordine di anni) quindi bassi consumi e la possibilità di realizzare un’ampia rete che possa supportare tante unità. Per questo elaborato è stata utilizzata la tecnologia LoRa, creata da Semtech. Essa lavora nelle frequenze ISM designate per le varie zone geografiche del mondo, presenta un Livello Fisico personalizzato ispirato alla modulazione CSS e un Livello MAC che si basa sul protocollo ALOHA puro. Lo scopo di questo elaborato è realizzare delle misure delle prestazioni in ambiente indoor tramite l’utilizzo di due nodi (End Devices) e un gateway. Sono state sviluppate due applicazioni Java per realizzare la comunicazione tra i dispositivi. Le misure sono state realizzate inizialmente con un nodo singolo, per osservarne il tasso di perdita di pacchetti (packet loss rate) e l’attenuazione di potenza sul canale (channel loss). Successivamente sono state inviate trasmissioni da entrambi i nodi, prima separatamente e poi in contemporanea, per valutare l’interferenza tra invii di messaggi con uguali impostazioni nello stesso canale. Per fare ciò è stato utilizzato un modello della comunicazione di canale che tiene conto del path loss e dello shadowing log-normale. I risultati hanno mostrato che con un solo nodo si tratta di una tecnologia affidabile. Per quanto riguarda i risultati delle misure con interferente è emersa una differenza con i valori attesi fino al 20%. Nell’elaborato vengono discussi i risultati ottenuti e possibili sviluppi futuri per questo tipo di sperimentazione.

Wireless Network Analytics for Next Generation Spectrum Awareness

The importance of networks, in their broad sense, is rapidly and massively growing in modern-day society thanks to unprecedented communication capabilities offered by technology. In this context, the radio spectrum will be a primary resource to be preserved and not wasted. Therefore, the need for intelligent and automatic systems for in-depth spectrum analysis and monitoring will pave the way for a new set of opportunities and potential challenges. This thesis proposes a novel framework for automatic spectrum patrolling and the extraction of wireless network analytics. It aims to enhance the physical layer security of next generation wireless networks through the extraction and the analysis of dedicated analytical features. The framework consists of a spectrum sensing phase, carried out by a patrol composed of numerous radio-frequency (RF) sensing devices, followed by the extraction of a set of wireless network analytics. The methodology developed is blind, allowing spectrum sensing and analytics extraction of a network whose key features (i.e., number of nodes, physical layer signals, medium access protocol (MAC) and routing protocols) are unknown. Because of the wireless medium, over-the-air signals captured by the sensors are mixed; therefore, blind source separation (BSS) and measurement association are used to estimate the number of sources and separate the traffic patterns. After the separation, we put together a set of methodologies for extracting useful features of the wireless network, i.e., its logical topology, the application-level traffic patterns generated by the nodes, and their position. The whole framework is validated on an ad-hoc wireless network accounting for MAC protocol, packet collisions, nodes mobility, the spatial density of sensors, and channel impairments, such as path-loss, shadowing, and noise. The numerical results obtained by extensive and exhaustive simulations show that the proposed framework is consistent and can achieve the required performance.

Simulation of the Interaction Mean Free Path between Neutrons and TRISO Particles

The interaction mean free path between neutrons and TRISO particles is simulated using scripts written in MATLAB to solve the increasing error present with an increase in the packing factor in the reactor physics code Serpent. Their movement is tracked both in an unbounded and in a bounded space. Their track is calculated, depending on the program, linearly directly using the position vectors of the neutrons and the surface equations of all the fuel particles; by dividing the space in multiple subspaces, each of which contain a fraction of the total number of particles, and choosing the particles from those subspaces through which the neutron passes through; or by choosing the particles that lie within an infinite cylinder formed on the movement axis of the neutron. The estimate from the current analytical model, based on an exponential distribution, for the mean free path, utilized by Serpent, is used as a reference result. The results from the implicit model in Serpent imply a too long mean free path with high packing factors. The received results support this observation by producing, with a packing factor of 17 %, approximately 2.46 % shorter mean free path compared to the reference model. This is supported by the packing factor experienced by the neutron, the simulation of which resulted in a 17.29 % packing factor. It was also observed that the neutrons leaving from the surfaces of the fuel particles, in contrast to those starting inside the moderator, do not follow the exponential distribution. The current model, as it is, is thus not valid in the determination of the free path lengths of the neutrons.

RNS based programmable multi-mode decimation filter for WCDMA and WiMAX

The recent trends envisage multi-standard architectures as a promising solution for the future wireless transceivers to attain higher system capacities and data rates. The computationally intensive decimation filter plays an important role in channel selection for multi-mode systems. An efficient reconfigurable implementation is a key to achieve low power consumption. To this end, this paper presents a dual-mode Residue Number System (RNS) based decimation filter which can be programmed for WCDMA and 802.16e standards. Decimation is done using multistage, multirate finite impulse response (FIR) filters. These FIR filters implemented in RNS domain offers high speed because of its carry free operation on smaller residues in parallel channels. Also, the FIR filters exhibit programmability to a selected standard by reconfiguring the hardware architecture. The total area is increased only by 24% to include WiMAX compared to a single mode WCDMA transceiver. In each mode, the unused parts of the overall architecture is powered down and bypassed to attain power saving. The performance of the proposed decimation filter in terms of critical path delay and area are tabulated.

Dual-mode RNS based programmable decimation filter for WCDMA and WLANa

The recent trends envisage multi-standard architectures as a promising solution for the future wireless transceivers. The computationally intensive decimation filter plays an important role in channel selection for multi-mode systems. An efficient reconfigurable implementation is a key to achieve low power consumption. To this end, this paper presents a dual-mode Residue Number System (RNS) based decimation filter which can be programmed for WCDMA and 802.11a standards. Decimation is done using multistage, multirate finite impulse response (FIR) filters. These FIR filters implemented in RNS domain offers high speed because of its carry free operation on smaller residues in parallel channels. Also, the FIR filters exhibit programmability to a selected standard by reconfiguring the hardware architecture. The total area is increased only by 33% to include WLANa compared to a single mode WCDMA transceiver. In each mode, the unused parts of the overall architecture is powered down and bypassed to attain power saving. The performance of the proposed decimation filter in terms of critical path delay and area are tabulated

Free electromagnetic field in Riemannian space-time via DKP theory

We study the massless Duffin-Kemmer-Petiau (DKP) equation in Riemannian space-times, particularly the massless spin 1 sector which reproduces the free Maxwell's equations.

Path Optimization in Free Energy Calculations

Free energy calculations are a computational method for determining thermodynamic quantities, such as free energies of binding, via simulation.

Currently, due to computational and algorithmic limitations, free energy calculations are limited in scope.

In this work, we propose two methods for improving the efficiency of free energy calculations.

First, we expand the state space of alchemical intermediates, and show that this expansion enables us to calculate free energies along lower variance paths.

We use Q-learning, a reinforcement learning technique, to discover and optimize paths at low computational cost.

Second, we reduce the cost of sampling along a given path by using sequential Monte Carlo samplers.

We develop a new free energy estimator, pCrooks (pairwise Crooks), a variant on the Crooks fluctuation theorem (CFT), which enables decomposition of the variance of the free energy estimate for discrete paths, while retaining beneficial characteristics of CFT.

Combining these two advancements, we show that for some test models, optimal expanded-space paths have a nearly 80% reduction in variance relative to the standard path.

Additionally, our free energy estimator converges at a more consistent rate and on average 1.8 times faster when we enable path searching, even when the cost of path discovery and refinement is considered.

Evaluation of Tottenham Thinking Space Pilot: Final Report. Research Report 11.

This reports summarises research that began in March 2014 and was completed in October 2015 by an experienced inter-disciplinary research team from the Centre for Social Justice and Change and Psycho-Social Research Group, School of Social Sciences, the University of East London (UEL) and included Dr Yang Li from the Centre for Geo-Information Studies, UEL, for the first phase of the study. Tottenham ‘Thinking Space’ (TTS) was a pilot therapeutic initiative based in local communities and delivered by the Tavistock & Portman NHS Foundation Trust and funded by the London Borough of Haringey Directorate of Public Health. TTS aimed to improve mental health and enable and empower local communities. TTS was situated within a mental health agenda that was integral to Haringey’s Health and Wellbeing Strategy 2012-2015 and aimed to encourage people to help themselves and each other and develop confident communities. On the one hand TTS was well-suited to this agenda, but, on the other, participants were resistant to, and were trying to free themselves from labelling that implied ‘mental health difficulties’. A total of 243 meetings were held and 351 people attended 1,716 times. The majority of participants attended four times or less, and 33 people attended between 5 and 10 times and 39 people attended over 10 times. Attending a small number of times does not necessarily mean that the attendee was not helped. Attendees reflected the ethnic diversity of Tottenham; 29 different ethnic groups attended. The opportunity to meet with people from different cultural backgrounds in a safe space was highly valued by attendees. Similarly, participants valued the wide age range represented and felt that they benefited from listening to inter-generational experiences. The majority of participants were women (72%) and they were instrumental in initiating further Thinking Spaces, topic specific meetings, the summer programme of activities for mothers and young children and training to meet their needs. The community development worker had a key role in implementing the initiative and sustaining its growth throughout the pilot period. We observed that TTS attracted those whose life experiences were marked by personal struggle and trauma. Many participants felt safe enough to disclose mental health difficulties (85% of those who completed a questionnaire). Participants also came seeking a stronger sense of community in their local area. Key features of the meetings are that they are democratic, non-judgemental, respectful, and focussed on encouraging everyone to listen and to try to understand. We found that the therapeutic method was put in place by high quality facilitators and health and personal outcomes for participants were consistent with those predicted by the underpinning psychoanalytical and systemic theories. Outcomes included a reduction in anxieties and improved personal and social functioning; approximately two thirds of those who completed a questionnaire felt better understood, felt more motivated and more hopeful for the future. The overwhelming majority of survey respondents also felt good about contributing to their community, said that they were more able to cooperate with others and accepting of other cultures, and had made new friends. Participants typically had a better understanding of their current situation and how to take positive action; of those who completed a questionnaire, over half felt more confident to seek support for a personal issue and to contact services. Members of TTS supported each other and instilled hope and build community-mindedness that reduced social isolation.

Experimental investigation on adaptive robust controller designs applied to a free-floating space manipulator

This paper aims to formulate and investigate the application of various nonlinear H(infinity) control methods to a fiee-floating space manipulator subject to parametric uncertainties and external disturbances. From a tutorial perspective, a model-based approach and adaptive procedures based on linear parametrization, neural networks and fuzzy systems are covered by this work. A comparative study is conducted based on experimental implementations performed with an actual underactuated fixed-base planar manipulator which is, following the DEM concept, dynamically equivalent to a free-floating space manipulator. (C) 2011 Elsevier Ltd. All rights reserved.

Optimização do posicionamento de câmaras de vídeo-vigilância

Dissertação de Mestrado em Engenharia de Redes de Comunicação e Multimédia

Reliability and availability in reconfigurable computing: a basis for a common solution

Dynamically reconfigurable SRAM-based field-programmable gate arrays (FPGAs) enable the implementation of reconfigurable computing systems where several applications may be run simultaneously, sharing the available resources according to their own immediate functional requirements. To exclude malfunctioning due to faulty elements, the reliability of all FPGA resources must be guaranteed. Since resource allocation takes place asynchronously, an online structural test scheme is the only way of ensuring reliable system operation. On the other hand, this test scheme should not disturb the operation of the circuit, otherwise availability would be compromised. System performance is also influenced by the efficiency of the management strategies that must be able to dynamically allocate enough resources when requested by each application. As those resources are allocated and later released, many small free resource blocks are created, which are left unused due to performance and routing restrictions. To avoid wasting logic resources, the FPGA logic space must be defragmented regularly. This paper presents a non-intrusive active replication procedure that supports the proposed test methodology and the implementation of defragmentation strategies, assuring both the availability of resources and their perfect working condition, without disturbing system operation.

Scale-free networks and scalable interdomain routing

Trabalho apresentado no âmbito do Mestrado em Engenharia Informática, como requisito parcial para obtenção do grau de Mestre em Engenharia Informática

Kommentierte Übersetzung des NASA-Berichtes „Pioneering Space: NASA’s Next Steps on the Path to Mars“ vom Englischen ins Deutsche

Die Bachelorarbeit besteht aus der Übersetzung des NASA-Berichtes „Pioneering Space: NASA’s Next Steps on the Path to Mars“ vom Englischen ins Deutsche und einer Textanalyse nach dem Analysemodell von Christiane Nord. Dieser Analyseansatz wird grob nach den sog. textexternen und textinternen Faktoren aufgeteilt. Zu den Besonderheiten und Herausforderungen der Übersetzung werden u.a. das hohe fachsprachliche Textniveau sowie diverse Abkürzungen und Abteilungsnamen innerhalb der NASA, die im Bericht auftauchen, gehören. Da darüber hinaus die Berichte und Kommunikation in der Weltraumszene hauptsächlich in englischer Sprache erfolgt, muss ein Kompromiss gefunden werden, um die Wörter so im Text einzubringen, dass der Textfluss nicht übertrieben gestört wird.

Spin-labeling coronary MR angiography with steady-state free precession and radial k-space sampling: initial results in healthy volunteers.

The purpose of this study was to prospectively compare free-breathing navigator-gated cardiac-triggered three-dimensional steady-state free precession (SSFP) spin-labeling coronary magnetic resonance (MR) angiography performed by using Cartesian k-space sampling with that performed by using radial k-space sampling. A new dedicated placement of the two-dimensional selective labeling pulse and an individually adjusted labeling delay time approved by the institutional review board were used. In 14 volunteers (eight men, six women; mean age, 28.8 years) who gave informed consent, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), vessel sharpness, vessel length, and subjective image quality were investigated. Differences between groups were analyzed with nonparametric tests (Wilcoxon, Pearson chi2). Radial imaging, as compared with Cartesian imaging, resulted in a significant reduction in the severity of motion artifacts, as well as an increase in SNR (26.9 vs 12.0, P < .05) in the coronary arteries and CNR (23.1 vs 8.8, P < .05) between the coronary arteries and the myocardium. A tendency toward improved vessel sharpness and vessel length was also found with radial imaging. Radial SSFP imaging is a promising technique for spin-labeling coronary MR angiography.