67,483 research outputs found
Geospatial Narratives and their Spatio-Temporal Dynamics: Commonsense Reasoning for High-level Analyses in Geographic Information Systems
The modelling, analysis, and visualisation of dynamic geospatial phenomena
has been identified as a key developmental challenge for next-generation
Geographic Information Systems (GIS). In this context, the envisaged
paradigmatic extensions to contemporary foundational GIS technology raises
fundamental questions concerning the ontological, formal representational, and
(analytical) computational methods that would underlie their spatial
information theoretic underpinnings.
We present the conceptual overview and architecture for the development of
high-level semantic and qualitative analytical capabilities for dynamic
geospatial domains. Building on formal methods in the areas of commonsense
reasoning, qualitative reasoning, spatial and temporal representation and
reasoning, reasoning about actions and change, and computational models of
narrative, we identify concrete theoretical and practical challenges that
accrue in the context of formal reasoning about `space, events, actions, and
change'. With this as a basis, and within the backdrop of an illustrated
scenario involving the spatio-temporal dynamics of urban narratives, we address
specific problems and solutions techniques chiefly involving `qualitative
abstraction', `data integration and spatial consistency', and `practical
geospatial abduction'. From a broad topical viewpoint, we propose that
next-generation dynamic GIS technology demands a transdisciplinary scientific
perspective that brings together Geography, Artificial Intelligence, and
Cognitive Science.
Keywords: artificial intelligence; cognitive systems; human-computer
interaction; geographic information systems; spatio-temporal dynamics;
computational models of narrative; geospatial analysis; geospatial modelling;
ontology; qualitative spatial modelling and reasoning; spatial assistance
systemsComment: ISPRS International Journal of Geo-Information (ISSN 2220-9964);
Special Issue on: Geospatial Monitoring and Modelling of Environmental
Change}. IJGI. Editor: Duccio Rocchini. (pre-print of article in press
Long-term Tracking in the Wild: A Benchmark
We introduce the OxUvA dataset and benchmark for evaluating single-object
tracking algorithms. Benchmarks have enabled great strides in the field of
object tracking by defining standardized evaluations on large sets of diverse
videos. However, these works have focused exclusively on sequences that are
just tens of seconds in length and in which the target is always visible.
Consequently, most researchers have designed methods tailored to this
"short-term" scenario, which is poorly representative of practitioners' needs.
Aiming to address this disparity, we compile a long-term, large-scale tracking
dataset of sequences with average length greater than two minutes and with
frequent target object disappearance. The OxUvA dataset is much larger than the
object tracking datasets of recent years: it comprises 366 sequences spanning
14 hours of video. We assess the performance of several algorithms, considering
both the ability to locate the target and to determine whether it is present or
absent. Our goal is to offer the community a large and diverse benchmark to
enable the design and evaluation of tracking methods ready to be used "in the
wild". The project website is http://oxuva.netComment: To appear at ECCV 201
Quasar broad absorption line variability measurements using reconstructions of un-absorbed spectra
We present a two-epoch Sloan Digital Sky Survey and Gemini/GMOS+William
Herschel Telescope/ISIS variability study of 50 broad absorption line quasars
of redshift range 1.9 < z < 4.2, containing 38 Si IV and 59 C IV BALs and
spanning rest-frame time intervals of approximately 10 months to 3.7 years. We
find that 35/50 quasars exhibit one or more variable BALs, with 58% of Si IV
and 46% of C IV BALs showing variability across the entire sample. On average,
Si IV BALs show larger fractional change in BAL pseudo equivalent width than C
IV BALs, as referenced to an unabsorbed continuum+emission-line spectrum
constructed using non-negative matrix factorisation. No correlation is found
between BAL variability and quasar luminosity, suggesting that ionizing
continuum changes do not play a significant role in BAL variability (assuming
the gas is in photoionization equilibrium with the ionizing continuum). A
subset of 14 quasars have one variable BAL from each of Si IV and C IV with
significant overlap in velocity space and for which variations are in the same
sense (strengthening or weakening) and which appear to be correlated (98%
confidence). We find examples of both appearing and disappearing BALs in
weaker/shallower lines with disappearance rates of 2.3% for C IV and 5.3% for
Si IV, suggesting average lifetimes of 142 and 43 years respectively. We
identify 5 objects in which the BAL is coincident with the broad emission-line,
but appears to cover only the continuum source. Assuming a clumpy inhomogeneous
absorber model and a typical size for the continuum source, we infer a maximum
cloud radius of 10^13 to 10^14 cm, assuming Eddington limited accretion.Comment: Accepted for publication in MNRAS. 22 pages, 12 figures, 7 table
Microeconomic Structure determines Macroeconomic Dynamics. Aoki defeats the Representative Agent
Masanao Aoki developed a new methodology for a basic problem of economics:
deducing rigorously the macroeconomic dynamics as emerging from the
interactions of many individual agents. This includes deduction of the fractal
/ intermittent fluctuations of macroeconomic quantities from the granularity of
the mezo-economic collective objects (large individual wealth, highly
productive geographical locations, emergent technologies, emergent economic
sectors) in which the micro-economic agents self-organize.
In particular, we present some theoretical predictions, which also met
extensive validation from empirical data in a wide range of systems: - The
fractal Levy exponent of the stock market index fluctuations equals the Pareto
exponent of the investors wealth distribution. The origin of the macroeconomic
dynamics is therefore found in the granularity induced by the wealth / capital
of the wealthiest investors. - Economic cycles consist of a Schumpeter
'creative destruction' pattern whereby the maxima are cusp-shaped while the
minima are smooth. In between the cusps, the cycle consists of the sum of 2
'crossing exponentials': one decaying and the other increasing.
This unification within the same theoretical framework of short term market
fluctuations and long term economic cycles offers the perspective of a genuine
conceptual synthesis between micro- and macroeconomics. Joining another giant
of contemporary science - Phil Anderson - Aoki emphasized the role of rare,
large fluctuations in the emergence of macroeconomic phenomena out of
microscopic interactions and in particular their non self-averaging, in the
language of statistical physics. In this light, we present a simple stochastic
multi-sector growth model.Comment: 42 pages, 6 figure
Vision-based toddler tracking at home
This paper presents a vision-based toddler tracking system for detecting risk factors of a toddler's fall within the home environment. The risk factors have environmental and behavioral aspects and the research in this paper focuses on the behavioral aspects. Apart from common image processing tasks such as background subtraction, the vision-based toddler tracking involves human classification, acquisition of motion and position information, and handling of regional merges and splits. The human classification is based on dynamic motion vectors of the human body. The center of mass of each contour is detected and connected with the closest center of mass in the next frame to obtain position, speed, and directional information. This tracking system is further enhanced by dealing with regional merges and splits due to multiple object occlusions. In order to identify the merges and splits, two directional detections of closest region centers are conducted between every two successive frames. Merges and splits of a single object due to errors in the background subtraction are also handled. The tracking algorithms have been developed, implemented and tested
Multiple object tracking using a neural cost function
This paper presents a new approach to the tracking of multiple objects in CCTV surveillance using a combination of simple neural cost functions based on Self-Organizing Maps, and a greedy assignment algorithm. Using a reference standard data set and an exhaustive search algorithm for benchmarking, we show that the cost function plays the most significant role in realizing high levels of performance. The neural cost function’s context-sensitive treatment of appearance, change of appearance and trajectory yield better tracking than a simple, explicitly designed cost function. The algorithm matches 98.8% of objects to within 15 pixels
The role of the ventral intraparietal area (VIP/pVIP) in parsing optic flow into visual motion caused by self-motion and visual motion produced by object-motion
Retinal image motion is a composite signal that contains information about two behaviourally significant factors: self-motion and the movement of environmental objects. It is thought that the brain separates the two relevant signals, and although multiple brain regions have been identified that respond selectively to the composite optic flow signal, which brain region(s) perform the parsing process remains unknown. Here, we present original evidence that the putative human ventral intraparietal area (pVIP), a region known to receive optic flow signals as well as independent self-motion signals from other sensory modalities, plays a critical role in the parsing process and acts to isolate object-motion. We localised pVIP using its multisensory response profile, and then tested its relative responses to simulated object-motion and self-motion stimuli; results indicated that responses were much stronger in pVIP to stimuli that specified object-motion. We report two further observations that will be significant for the future direction of research in this area; firstly, activation in pVIP was suppressed by distant stationary objects compared to the absence of objects or closer objects. Secondly, we describe several other brain regions that share with pVIP selectivity for visual object-motion over visual self-motion as well as a multisensory response
The (In)Difference engine: explaining the disappearance of diversity in the design of the personal computer
At the time of writing there is a clear perception of all office computers as being more or less identical. Discussion with users entails repetitive rhetoric as they describe a landscape of boring beige boxes. The office PC is indeed a ‘clone’ - an identical, characterless copy of a bland original.
Through the exploration of an archive of computer manufacturer’s catalogues, this article shows how previous, innovative forms of the computer informed by cultural references as diverse as science fiction, accepted gender roles and the discourse of status as displayed through objects, have been systematically replaced by the adoption of a ‘universal’ design informed only by the nondescript, self-referential world of office equipment.
The acceptance of this lack of innovation in the design of such a truly global, mass-produced, multi-purpose technological artefact has had an enormous effect on the conception, perception and consumption of the computer, and possibly of information technology itself. The very anonymity of the PC has created an attitude of indifference at odds with its potential.</p
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