959 resultados para User Space Memory
Resumo:
Extensible systems allow services to be configured and deployed for the specific needs of individual applications. This paper describes a safe and efficient method for user-level extensibility that requires only minimal changes to the kernel. A sandboxing technique is described that supports multiple logical protection domains within the same address space at user-level. This approach allows applications to register sandboxed code with the system, that may be executed in the context of any process. Our approach differs from other implementations that require special hardware support, such as segmentation or tagged translation look-aside buffers (TLBs), to either implement multiple protection domains in a single address space, or to support fast switching between address spaces. Likewise, we do not require the entire system to be written in a type-safe language, to provide fine-grained protection domains. Instead, our user-level sandboxing technique requires only paged-based virtual memory support, and the requirement that extension code is written either in a type-safe language, or by a trusted source. Using a fast method of upcalls, we show how our sandboxing technique for implementing logical protection domains provides significant performance improvements over traditional methods of invoking user-level services. Experimental results show our approach to be an efficient method for extensibility, with inter-protection domain communication costs close to those of hardware-based solutions leveraging segmentation.
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The paper examines the role of shared spaces in divided cities in promoting future sustainable communities and spaces described as inclusive to all. It addresses the current challenges that prevent such inclusiveness and suggests future trends of its development to be of benefit to the wider city community. It explains how spaces in divided cities are carved up into perceived ownerships and territorialized areas, which increases tension on the shared space between territories; the control of which can often lead to inter-community disputes. The paper reports that common shared space in-between conflicting communities takes on increased importance since the nature of the conflict places emphasis on communities’ confidence, politically and socially, while also highlighting the necessity for confidence in inclusion and feeling secure in the public domain. In order to achieve sustainable environments, strategies to promote shared spaces require further focus on the significance of everyday dynamics as essential aspects for future integration and conflict resolution.
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Graffiti, Memory and Contested Space: Mnemonic Initiatives Following Periods of Trauma and/or Repression in Buenos Aires, Argentina This thesis concerns the popular articulation ofmemory following periods or incidents of trauma in Argentina. I am interested in how groups lay claim to various public spaces in the city and how they convert these spaces into mnemonic battlegrounds. In considering these spaces of trauma and places of memory, I am primarily interested in how graffiti writing (stencils, spray-paint, signatures, etchings, wall-paintings, murals and installations) is used to make these spaces transmit particular memories that impugn official versions of the past. This thesis draws on literatures focused on popular/public memory. Scholars argue that memory is socially constructed and thus actively contested. Marginal initiatives such as graffiti writing challenge the memory projects of the state as well as state projects that are perceived by citizens to be 'inadequate,' 'inappropriate,' and/or as promoting the erasure of memory. Many of these initiatives are a reaction to the proreconciliation and pro-oblivion strategies of previous governments. I outline that the history of silences and impunity, and a longstanding emphasis on reconciliation at the expense of truth and justice has created an environment of vulnerable memory in Argentina. Popular memory entrepreneurs react by aggressively articulating their memories in time and in space. As a result of this intense memory work, the built landscape in Buenos Aires is dotted with mnemonic initiatives that aim to contradict or subvert officially sanctioned memories. I also suggest that memory workers in Argentina persistently and carefially use the sites of trauma as well as key public spaces to ensure official as well as popular audiences . The data for this project was collected in five spaces in Buenos Aires, the Plaza de Mayo, Plaza Congreso, La Republica Cromanon nightclub, Avellaneda Train Station and El Olimpo, a former detention centre from the military dictatorship.
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The discrete Fourier transmission spread OFDM DFTS-OFDM) based single-carrier frequency division multiple access (SC-FDMA) has been widely adopted due to its lower peak-to-average power ratio (PAPR) of transmit signals compared with OFDM. However, the offset modulation, which has lower PAPR than general modulation, cannot be directly applied into the existing SC-FDMA. When pulse-shaping filters are employed to further reduce the envelope fluctuation of transmit signals of SC-FDMA, the spectral efficiency degrades as well. In order to overcome such limitations of conventional SC-FDMA, this paper for the first time investigated cyclic prefixed OQAMOFDM (CP-OQAM-OFDM) based SC-FDMA transmission with adjustable user bandwidth and space-time coding. Firstly, we propose CP-OQAM-OFDM transmission with unequally-spaced subbands. We then apply it to SC-FDMA transmission and propose a SC-FDMA scheme with the following features: a) the transmit signal of each user is offset modulated single-carrier with frequency-domain pulse-shaping; b) the bandwidth of each user is adjustable; c) the spectral efficiency does not decrease with increasing roll-off factors. To combat both inter-symbolinterference and multiple access interference in frequencyselective fading channels, a joint linear minimum mean square error frequency domain equalization using a prior information with low complexity is developed. Subsequently, we construct space-time codes for the proposed SC-FDMA. Simulation results confirm the powerfulness of the proposed CP-OQAM-OFDM scheme (i.e., effective yet with low complexity).
Resumo:
Searching in a dataset for elements that are similar to a given query element is a core problem in applications that manage complex data, and has been aided by metric access methods (MAMs). A growing number of applications require indices that must be built faster and repeatedly, also providing faster response for similarity queries. The increase in the main memory capacity and its lowering costs also motivate using memory-based MAMs. In this paper. we propose the Onion-tree, a new and robust dynamic memory-based MAM that slices the metric space into disjoint subspaces to provide quick indexing of complex data. It introduces three major characteristics: (i) a partitioning method that controls the number of disjoint subspaces generated at each node; (ii) a replacement technique that can change the leaf node pivots in insertion operations; and (iii) range and k-NN extended query algorithms to support the new partitioning method, including a new visit order of the subspaces in k-NN queries. Performance tests with both real-world and synthetic datasets showed that the Onion-tree is very compact. Comparisons of the Onion-tree with the MM-tree and a memory-based version of the Slim-tree showed that the Onion-tree was always faster to build the index. The experiments also showed that the Onion-tree significantly improved range and k-NN query processing performance and was the most efficient MAM, followed by the MM-tree, which in turn outperformed the Slim-tree in almost all the tests. (C) 2010 Elsevier B.V. All rights reserved.
Resumo:
SRAM-based FPGAs are in-field reconfigurable an unlimited number of times. This characteristic, together with their high performance and high logic density, proves to be very convenient for a number of ground and space level applications. One drawback of this technology is that it is susceptible to ionizing radiation, and this sensitivity increases with technology scaling. This is a first order concern for applications in harsh radiation environments, and starts to be a concern for high reliability ground applications. Several techniques exist for coping with radiation effects at user application. In order to be effective they need to be complemented with configuration memory scrubbing, which allows error mitigation and prevents failures due to error accumulation. Depending on the radiation environment and on the system dependability requirements, the configuration scrubber design can become more or less complex. This paper classifies and presents current and novel design methodologies and architectures for SRAM-based FPGAs, and in particular for Xilinx Virtex-4QV/5QV, configuration memory scrubbers.
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Book review: Eigler, Friederike, and Jens Kugele, eds. Heimat. At the Intersection of Memory and Space. Berlin: de Gruyter, 2012. 268 pp. $126.00 hardcover.
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Palaces, as an architectural typology, can be found in recreation Quintas that surrounded the main cities in Portugal, which preserved its rural character since the 16th century until the middle of the 19th century. Consisting of cultivated land and farm buildings, the palace of the Quinta was the owner´s temporary residence, for summer holidays and festive events, with gardens, pavilions, fountains and lakes for recreational purposes and leisure. The focus on palaces, as a historic building and as in need of new uses, clearly shows how current the debate on contemporary interventions in this heritage typology is. Interventions in architectural heritage require multidisciplinary teams to identify conservation strategies which enable a qualified use of its spaces, such as for example the experience of security and well-being, which can contribute to a better quality of life and simultaneously to the quality of the urban environment. This paper presents the Palace of Quinta Alegre and its rehabilitation project for contemporary use and public esteem, both of which are considered fundamental prerequisites for its sustainable maintenance in space, in time and in memory. [versão Portuguesa] Sob a denominação de tipologia arquitectónica, o edifício Palácio pode ser encontrado nas Quintas de Recreio que rodeavam as principais cidades Portuguesas, tendo preservado o seu carácter rural, desde o século XVI até metade do século XIX. Consistindo as Quintas em terra cultivada e edifícios rurais, o Palácio da Quinta consistia na residência temporária do proprietário, para férias de verão e eventos comemorativos, dispondo de jardins, pavilhões, fontes e lagos para recreação e lazer. O tema dos Palácios, entendido como edifício histórico que procura novos usos, demonstra como é actual o debate sobre intervenções contemporâneas nesta tipologia de valor patrimonial. A intervenção em património arquitectónico requer a definição de estratégias de conservação por equipas multidisciplinares que permitam estabelecer um uso qualificado dos seus espaços, proporcionando experiências sensoriais de bem-estar e segurança, contribuindo para uma melhor qualidade de vida e, simultaneamente, para a qualidade do ambiente urbano em que se insere. Este artigo tem por objectivo apresentar o Palácio da Quinta Alegre e o projecto de reabilitação, devolvendo-o a um uso contemporâneo e à estima pública, factores fundamentais para a sua manutenção sustentável no espaço, no tempo e na memória.
Resumo:
This paper documents the empowering process of a group of public housing residents through different design probing exercises. These exercises worked along with existing social processes without any involvement of designers. This paper shows how a design researcher devised a series of probing tools called "empowerment games" with a group of active users. These games are self-learning tools for making the abstract language of design legible to users. The main purpose of this intitiative was to change the preconception of govenmental bodies and professional designers of the passivity of the users with regard to their designed environment. This was the first case of the application of a participatory design process in Hong Kong subsidized housing. Design empathy is a central skill when working with users throughout the whole design research project.
Resumo:
Some Engineering Faculties are turning to the problem-based learning (PBL)paradigm to engender necessary skills and competence in their graduates. Since, at the same time, some Faculties are moving towards distance education, questions are being asked about the effectiveness of PBL for technical fields such as Engineering when delivered in virtual space. This paper outlines an investigation of how student attributes affect their learning experience in PBL courses offered in virtual space. A frequency distribution was superimposed on the outcome space of a phenomenographical study on a suitable PBL course to investigate the effect of different student attributes on the learning experience. It was discovered that the quality, quantity, and style of facilitator interaction had the greatest impact on the student learning experience. This highlights the need to establish consistent student interaction plans and to set, and ensure compliance with, minimum standards with respect to facilitation and student interactions.
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This thesis investigates the problem of robot navigation using only landmark bearings. The proposed system allows a robot to move to a ground target location specified by the sensor values observed at this ground target posi- tion. The control actions are computed based on the difference between the current landmark bearings and the target landmark bearings. No Cartesian coordinates with respect to the ground are computed by the control system. The robot navigates using solely information from the bearing sensor space. Most existing robot navigation systems require a ground frame (2D Cartesian coordinate system) in order to navigate from a ground point A to a ground point B. The commonly used sensors such as laser range scanner, sonar, infrared, and vision do not directly provide the 2D ground coordi- nates of the robot. The existing systems use the sensor measurements to localise the robot with respect to a map, a set of 2D coordinates of the objects of interest. It is more natural to navigate between the points in the sensor space corresponding to A and B without requiring the Cartesian map and the localisation process. Research on animals has revealed how insects are able to exploit very limited computational and memory resources to successfully navigate to a desired destination without computing Cartesian positions. For example, a honeybee balances the left and right optical flows to navigate in a nar- row corridor. Unlike many other ants, Cataglyphis bicolor does not secrete pheromone trails in order to find its way home but instead uses the sun as a compass to keep track of its home direction vector. The home vector can be inaccurate, so the ant also uses landmark recognition. More precisely, it takes snapshots and compass headings of some landmarks. To return home, the ant tries to line up the landmarks exactly as they were before it started wandering. This thesis introduces a navigation method based on reflex actions in sensor space. The sensor vector is made of the bearings of some landmarks, and the reflex action is a gradient descent with respect to the distance in sensor space between the current sensor vector and the target sensor vec- tor. Our theoretical analysis shows that except for some fully characterized pathological cases, any point is reachable from any other point by reflex action in the bearing sensor space provided the environment contains three landmarks and is free of obstacles. The trajectories of a robot using reflex navigation, like other image- based visual control strategies, do not correspond necessarily to the shortest paths on the ground, because the sensor error is minimized, not the moving distance on the ground. However, we show that the use of a sequence of waypoints in sensor space can address this problem. In order to identify relevant waypoints, we train a Self Organising Map (SOM) from a set of observations uniformly distributed with respect to the ground. This SOM provides a sense of location to the robot, and allows a form of path planning in sensor space. The navigation proposed system is analysed theoretically, and evaluated both in simulation and with experiments on a real robot.