Foto-assemblage

FOTO-ASSEMBLAGE consiste em nomenclatura sugestionada para definir os trabalhos que tenho produzido a partir da junção de fotografias digitais. As elaborações e fundamentações desses trabalhos representam também o cerne das pesquisas que resultaram na presente dissertação. Em princípio, o termo foto-assemblage haveria de referir-se a questões técnicas ou formais dessa prática. Contudo, ao desenvolver as pesquisas alguns procedimentos acabaram por determinar certas nuances que revelaram aspectos comuns também em seus e conteúdos. Como resultado de construções artísticas juntando fotografias desde 2009, cheguei às composições sintéticas aqui apresentadas, construídas a partir de duas fotografias. Aventei o nome foto-assemblage por observar nas imagens resultantes ressalvas que as distinguiriam de certas convenções atribuídas à ideia de fotografia. Ao mesmo tempo, as referidas imagens proporiam um possível desdobramento ao entendimento de assemblage enquanto técnica artística. Ainda que não seja uma regra, fotografias revelam imagens de momentos. Em sua relação com a compreensão humana de tempo ou espaço, fotografias quase sempre contêm instâncias mínimas. Fotografias, contudo, podem ser também compreendidas como uma contração de um percurso de tempo. Toda imagem fotográfica pode ser assimilada como resultante de determinados acontecimentos anteriores e mesmo tida como elemento gerador de conseqüências futuras. Seguindo esse entendimento, o que proponho com a foto-assemblage é que essa lide com segmentos de tempo ou de espaço contidos numa mesma imagem. Essas fotografias originárias ganhariam uma nova atribuição, sendo retiradas de seu contexto original, serviriam de balizas do percurso de tempo ou espaço suprimido e subjetivado entre elas. Poeticamente, eventos ocorridos entre as fotografias originárias estariam contidos nas imagens produzidas. O termo assemblage foi incorporado às artes a partir de 1953, por Jean Dubuffet, para descrever trabalhos que seriam algo mais do que simples colagem. A ideia de assemblage se baseia no princípio de que todo e qualquer material ou objeto colhido de nosso mundo cotidiano pode ser incorporado a uma obra de arte, criando um novo conjunto, sem que perca seu sentido original. Esse objeto é arrancado de seu uso habitual e inserido num novo contexto, tecendo laços de relação com os demais elementos, construindo narrativas num novo ambiente, o da obra. Na ideia da foto-assemblage, entretanto, é sugerido uso das imagens fotográficas originárias não como objetos que estariam em um mundo cotidiano, mas sim como imagem na concepção do que seria uma entidade mental. Adoto como que uma visão mágica onde as imagens originárias e básicas estariam numa outra dimensão, num plano bidimensional, não manipulável por nós habitantes da tridimensionalidade. Nesse ambiente imaginário ou não, as fotografias são assentadas consolidando a foto-assemblage. Quando a foto-assemblage se concretiza, se corporifica numa mídia, sendo impressa para uma contemplação, ai então, passaria a integrar nosso mundo tridimensional. O resultado poderia ser admitido como um híbrido, uma terceira coisa, a partir de duas que já não se dissociam mais no ensejo de uma compreensão estética. Ao final da dissertação, apresento experiências práticas que resultaram em quatro séries de imagens em foto-assemblage. Cada série enfatiza aspectos peculiares do que denomino paisagem expandida, representando percursos de tempo, espaço ou trajetos entre o mundo concreto e mundos do inconsciente.

Collective motion of self-propelled particles: Stabilizing symmetric formations on closed curves

We provide feedback control laws to stabilize formations of multiple, unit speed particles on smooth, convex, and closed curves with definite curvature. As in previous work we exploit an analogy with coupled phase oscillators to provide controls which isolate symmetric particle formations that are invariant to rigid translation of all the particles. In this work, we do not require all particles to be able to communicate; rather we assume that inter-particle communication is limited and can be modeled by a fixed, connected, and undirected graph. Because of their unique spectral properties, the Laplacian matrices of circulant graphs play a key role. The methodology is demonstrated using a superellipse, which is a type of curve that includes circles, ellipses, and rounded rectangles. These results can be used in applications involving multiple autonomous vehicles that travel at constant speed around fixed beacons. ©2006 IEEE.

Label-Free Colorimetric Detection of Aqueous Mercury Ion (Hg2+) Using Hg2+-Modulated G-Quadruplex-Based DNAzymes

Mercury ion (Hg2+) is able to specifically bind to the thymine-thymine (T-T) base pair in a DNA duplex, thus providing a rationale for DNA-based selective detection of Hg2+ with various means. In this work, we for the first time utilize the Hg2+-mediated T-T base pair to modulate the proper folding of G-quadruplex DNAs and inhibit the DNAzyme activity, thereby pioneering a facile approach to sense Hg2+ with colorimetry. Two bimolecular DNA G-quadruplexes containing many T residues are adopted here, which function well in low- and high-salt conditions, respectively. These G-quadruplex DNAs are able to bind hemin to form the peroxidase-like DNAzymes in the folded state. Upon addition of Hg2+, the proper folding of G-quadruplex DNAs is inhibited due to the formation of T-Hg2+-T complex. Ibis is reflected by the notable change of the Soret band of hemin when investigated by using UV-vis absorption spectroscopy. As a result of Hg2+ inhibition, a sharp decrease in the catalytic activity toward the H2O2-mediated oxidation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)diammonium salt (ABTS) is observed, accompanied by a change in solution color. Through this approach, aqueous Hg2+ can be detected at 50 nM (10 ppb) with colorimetry in a facile way, with high selectivity against other metal ions.

SERS opens a new way in aptasensor for protein recognition with high sensitivity and selectivity

SERS aptasensors for protein recognition based on Au nanoparticles labeled with aptamers and Raman reporters have been developed, which opens a new way for protein recognition of high sensitivity and selectivity.

基于LBL声信标的AUV快速精确定位

长基线声学定位系统是水下机器人广泛应用的外部导航设备。以对"CR-02"6000m自治水下机器人(简称AUV)技术的深入开发为背景,提出在原有长基线(LBL)定位系统的基础上增加导航功能的方案。由于海水介质非均匀性与复杂的时空变化特性,给基于测距的位置计算带来很大困难。采用平均声速法计算耗时小而误差大,波阵面定位法误差小而耗时大。为解决这个矛盾,根据AUV深度传感器给出的深度信息,采用本征声线快速计算方法解算AUV的水平面位置。与波阵面法、平均声速法进行了综合比较。仿真实验表明该方法具有优良的性能,满足AUV导航需要。

深水机器人低成本导航系统的位置估计方法研究

依据6000米自治水下机器人及其长基线声学定位系统现有的导航设备,将测距声信标和机器人载体携带的低成本导航传感器:涡轮式计程仪,压力传感器以及TCM2电子罗盘测量的导航数据相融合,分别提出两种基于EKF的导航数据融合算法,对机器人的位置以及水流参数进行估计,解决复杂环境下的深水机器人位置估计问题.蒙特卡洛仿真实验和湖上试验数据后处理表明,设计的位置估计算法收敛快,精度高,计算时间小,能够满足深水机器人的导航需要.

基于测距声信标的深水机器人导航定位技术研究

基于水声测距的导航定位技术在水下机器人中获得广泛应用，并成为现今水下机器人技术的研究热点。不管从实际应用前景还是理论研究意义看，这项研究都具有巨大的研究价值，并极富挑战性。纯距离（Range-only）导航是对外部观测量仅有距离信息的一类导航问题的统称。本文研究了基于测距原理的“CR-02”AUV长基线定位系统的两方面问题，即长基线定位系统的应用及导航问题。 本文分别对测距系统存在不确定性和扰动情况下的接收性能、稳定性、检测延时估计以及距离修正、声传播特性对测距系统应用的影响进行了研究，设计了适用于微弱CW脉冲信号接收的高增益滤波放大器与检测电路，湖上试验和海上试验证明了声信标接收电路的优良性能。用蒙特卡洛方法对检测延时分布特征进行了统计分析，得到了检测延时的分布规律，该方法得到的检测延时结果和分布规律与实际物理实验完全吻合，为处理任意时变系统的延时特征提供了一种新的分析方法。在前人研究基础上，利用声线修正算法解决了长基线系统中的有关重要问题，这些方法在深海试验中得到成功应用，使得长基线系统更加可靠有效。提出一种新的垂线相交标定方法，根据几何原理直接求取声信标坐标。利用这个新方法，声信标位置标定精度大大提高，系统实现也相对简单，深海海上试验证明方法有效而可靠。 “CR-02”长基线定位系统仅具有对AUV的定位能力，但没有导航功能，为满足应用需要，本文以”CR-02”AUV为研究对象，在原有设备基础上扩展其导航功能，从而实现监控型AUV的导航能力。通过分析水下机器人导航系统能观性，制定了保证系统能观的机动航行策略，分别设计出水下机器人在三个声信标和固定单信标情况下的卡尔曼滤波导航方法。这些方法能够提高传统多信标系统下机器人导航的强容错能力和鲁棒性，还为水下机器人位置修正问题提供一种新方法。最后，在移动声信标条件下机器人导航问题深入分析基础上，提出主从式多UUV群体协作导航机制，给出了多UUV群体中随从UUV导航算法的计算机仿真结果。计算机仿真证明了方法的有效性和正确性。

In hot water: zooplankton and climate change

An overview is provided of the observed and potential future responses of zooplankton communities to global warming. I begin by describing the importance of zooplankton in ocean ecosystems and the attributes that make them sensitive beacons of climate change. Global warming may have even greater repercussions for marine ecosystems than for terrestrial ecosystems, because temperature influences water column stability, nutrient enrichment, and the degree of new production, and thus the abundance, size composition, diversity, and trophic efficiency of zooplankton. Pertinent descriptions of physical changes in the ocean in response to climate change are given as a prelude to a detailed discussion of observed impacts of global warming on zooplankton. These manifest as changes in the distribution of individual species and assemblages, in the timing of important life-cycle events, and in abundance and community structure. The most illustrative case studies, where climate has had an obvious, tangible impact on zooplankton and substantial ecosystem consequences, are presented. Changes in the distribution and phenology of zooplankton are faster and greater than those observed for terrestrial groups. Relevant projected changes in ocean conditions are then presented, followed by an exploration of potential future changes in zooplankton communities from the perspective of different modelling approaches. Researchers have used a range of modelling approaches on individual species and functional groups forced by output from climate models under future greenhouse gas emission scenarios. I conclude by suggesting some potential future directions in climate change research for zooplankton, viz. the use of richer zooplankton functional groups in ecosystem models; greater research effort in tropical systems; investigating climate change in conjunction with other human impacts; and a global zooplankton observing system.

Improving the ultra-low-power performance of IEEE 802.15.6 by adaptive synchronisation

In ultra-low data rate wireless sensor networks (WSNs) waking up just to listen to a beacon every superframe can be a major waste of energy. This study introduces MedMAC, a medium access protocol for ultra-low data rate WSNs that achieves significant energy efficiency through a novel synchronisation mechanism. The new draft IEEE 802.15.6 standard for body area networks includes a sub-class of applications such as medical implantable devices and long-term micro miniature sensors with ultra-low power requirements. It will be desirable for these devices to have 10 years or more of operation between battery changes, or to have average current requirements matched to energy harvesting technology. Simulation results are presented to show that the MedMAC allows nodes to maintain synchronisation to the network while sleeping through many beacons with a significant increase in energy efficiency during periods of particularly low data transfer. Results from a comparative analysis of MedMAC and IEEE 802.15.6 MAC show that MedMAC has superior efficiency with energy savings of between 25 and 87 for the presented scenarios. © 2011 The Institution of Engineering and Technology.

Secure D2D Communication in Large-Scale Cognitive Cellular Networks with Wireless Power Transfer

In this paper, we investigate secure device-to-device (D2D) communication in energy harvesting large-scale cognitive cellular networks. The energy constrained D2D transmitter harvests energy from multi-antenna equipped power beacons (PBs), and communicates with the corresponding receiver using the spectrum of the cellular base stations (BSs). We introduce a power transfer model and an information signal model to enable wireless energy harvesting and secure information transmission. In the power transfer model, we propose a new power transfer policy, namely, best power beacon (BPB) power transfer. To characterize the power transfer reliability of the proposed policy, we derive new closed-form expressions for the exact power outage probability and the asymptotic power outage probability with large antenna arrays at PBs. In the information signal model, we present a new comparative framework with two receiver selection schemes: 1) best receiver selection (BRS), and 2) nearest receiver selection (NRS). To assess the secrecy performance, we derive new expressions for the secrecy throughput considering the two receiver selection schemes using the BPB power transfer policies. We show that secrecy performance improves with increasing densities of PBs and D2D receivers because of a larger multiuser diversity gain. A pivotal conclusion is reached that BRS achieves better secrecy performance than NRS but demands more instantaneous feedback and overhead.

Secure D2D Communication in Large-Scale Cognitive Cellular Networks: A Wireless Power Transfer Model

In this paper, we investigate secure device-to-device (D2D) communication in energy harvesting large-scale cognitive cellular networks. The energy constrained D2D transmitter harvests energy from multiantenna equipped power beacons (PBs), and communicates with the corresponding receiver using the spectrum of the primary base stations (BSs). We introduce a power transfer model and an information signal model to enable wireless energy harvesting and secure information transmission. In the power transfer model, three wireless power transfer (WPT) policies are proposed: 1) co-operative power beacons (CPB) power transfer, 2) best power beacon (BPB) power transfer, and 3) nearest power beacon (NPB) power transfer. To characterize the power transfer reliability of the proposed three policies, we derive new expressions for the exact power outage probability. Moreover, the analysis of the power outage probability is extended to the case when PBs are equipped with large antenna arrays. In the information signal model, we present a new comparative framework with two receiver selection schemes: 1) best receiver selection (BRS), where the receiver with the strongest channel is selected; and 2) nearest receiver selection (NRS), where the nearest receiver is selected. To assess the secrecy performance, we derive new analytical expressions for the secrecy outage probability and the secrecy throughput considering the two receiver selection schemes using the proposed WPT policies. We presented Monte carlo simulation results to corroborate our analysis and show: 1) secrecy performance improves with increasing densities of PBs and D2D receivers due to larger multiuser diversity gain; 2) CPB achieves better secrecy performance than BPB and NPB but consumes more power; and 3) BRS achieves better secrecy performance than NRS but demands more instantaneous feedback and overhead. A pivotal conclusion- is reached that with increasing number of antennas at PBs, NPB offers a comparable secrecy performance to that of BPB but with a lower complexity.

Ultrasonic location system

Esta tese apresenta um sistema de localização baseado exclusivamente em ultrassons, não necessitando de recorrer a qualquer outra tecnologia. Este sistema de localização foi concebido para poder operar em ambientes onde qualquer outra tecnologia não pode ser utilizada ou o seu uso está condicionado, como são exemplo aplicações subaquáticas ou ambientes hospitalares. O sistema de localização proposto faz uso de uma rede de faróis fixos permitindo que estações móveis se localizem. Devido à necessidade de transmissão de dados e medição de distâncias foi desenvolvido um pulso de ultrassons robusto a ecos que permite realizar ambas as tarefas com sucesso. O sistema de localização permite que as estações móveis se localizem escutando apenas a informação em pulsos de ultrassons enviados pelos faróis usando para tal um algoritmo baseado em diferenças de tempo de chegada. Desta forma a privacidade dos utilizadores é garantida e o sistema torna-se completamente independente do número de utilizadores. Por forma a facilitar a implementação da rede de faróis apenas será necessário determinar manualmente a posição de alguns dos faróis, designados por faróis âncora. Estes irão permitir que os restantes faróis, completamente autónomos, se possam localizar através de um algoritmo iterativo de localização baseado na minimização de uma função de custo. Para que este sistema possa funcionar como previsto será necessário que os faróis possam sincronizar os seus relógios e medir a distância entre eles. Para tal, esta tese propõe um protocolo de sincronização de relógio que permite também obter as medidas de distância entre os faróis trocando somente três mensagens de ultrassons. Adicionalmente, o sistema de localização permite que faróis danificados possam ser substituídos sem comprometer a operabilidade da rede reduzindo a complexidade na manutenção. Para além do mencionado, foi igualmente implementado um simulador de ultrassons para ambientes fechados, o qual provou ser bastante preciso e uma ferramenta de elevado valor para simular o comportamento do sistema de localização sobre condições controladas.

In search of reliable centimeter-level indoor positioning: a smartphone-based approach

This thesis describes the design and implementation of a reliable centimeter-level indoor positioning system fully compatible with a conventional smartphone. The proposed system takes advantage of the smartphone audio I/O and processing capabilities to perform acoustic ranging in the audio band using non-invasive audio signals and it has been developed having in mind applications that require high accuracy, such as augmented reality, virtual reality, gaming and audio guides. The system works in a distributed operation mode, i.e. each smartphone is able to obtain its own position using only acoustic signals. To support the positioning system, a Wireless Sensor Network (WSN) of synchronized acoustic beacons is used. To keep the infrastructure in sync we have developed an Automatic Time Synchronization and Syntonization (ATSS) protocol with a standard deviation of the sync offset error below 1.25 μs. Using an improved Time Difference of Arrival (TDoA) estimation approach (which takes advantage of the beacon signals’ periodicity) and by performing Non-Line-of-Sight (NLoS) mitigation, we were able to obtain very stable and accurate position estimates with an absolute mean error of less than 10 cm in 95% of the cases and a mean standard deviation of 2.2 cm for a position refresh period of 350 ms.

Beacon

Artwork using Internet search engine technology to make people’s online desires, interests and orientations visible, presenting random search term enquiries in a variety of forms including a railway information sign, an art gallery installation and an online website. activity, curiosity and desire. The project sampled and analysed how ‘search terms’ were used by the public as live data. It then re-presented them on a website, in a gallery and latterly on a bespoke mechanical railway flap-sign, thus creating a snapshot of online enquiry at any give time. Beacon’s originality lies in the manner in which it has taken abstract digital data and found different expressions for it. Thus the work extends debates in media arts that focus on purely virtual and online expressions of data, by developing online information into new non-digital material forms and contexts such as railway signs. This research has been developed over a three year period. Initially with software only and then on receipt of AHRC small grant (£5000) with the lauded Italian manufacturer Solari of Udine, Italy and BFI Southbank. It represents the culmination of a body of research that asks whether live data can be used as material to make artworks. Beacon was specially developed for the Tate Britain programme 40 artists 40 days, produced in conjunction with the UK Olympic Games bid and intended to “create a unique countdown calendar that will focus attention on Britain’s exceptional creative talent”. The project is exhibited by the Tate website ‘Tate Online’ presently in perpetuity. The gallery version of this work is currently held in five private collections in the USA and is shown regularly in galleries around the world. The railway flap-sign is owned by BFI Southbank and will eventually be sited there permanently. All work is developed jointly and equally between Craighead and her collaborator, Jon Thomson, (Slade).