On landmark selection and sampling in high-dimensional data analysis

In recent years, the spectral analysis of appropriately defined kernel matrices has emerged as a principled way to extract the low-dimensional structure often prevalent in high-dimensional data. Here we provide an introduction to spectral methods for linear and nonlinear dimension reduction, emphasizing ways to overcome the computational limitations currently faced by practitioners with massive datasets. In particular, a data subsampling or landmark selection process is often employed to construct a kernel based on partial information, followed by an approximate spectral analysis termed the Nystrom extension. We provide a quantitative framework to analyse this procedure, and use it to demonstrate algorithmic performance bounds on a range of practical approaches designed to optimize the landmark selection process. We compare the practical implications of these bounds by way of real-world examples drawn from the field of computer vision, whereby low-dimensional manifold structure is shown to emerge from high-dimensional video data streams.Comment: 18 pages, 6 figures, submitted for publicatio

Control of protein phosphatase I in the dendrite

Communication between nerve cells is mediated by both electrical and chemical signals. Chemical neurotransmission can be further categorized into fast and slow components. Fast acting neurotransmitters directly influence neuronal electrical excitability by binding to cell surface receptors which serve as ligand-gated ion channels, thereby directly modulating membrane potential and cell firing. Neurotransmitter receptors may otherwise modulate neuronal excitability indirectly, by coupling to intracellular signalling pathways that impact on the functional activity of ligand- and voltage-gated ion channels, ion pumps, and the machinery for chemical neurotransmission. These indirect actions are relatively slow, and often involve cascades of protein phosphorylation which serve to alter the biochemical activities of substrate proteins, and hence cellular physiology

Documentation and dissemination of the sculptural elements of Canada's parliamentary buildings: Methodology development and Volution, a case study

Parliament Hill consists of four historic gothic revival buildings, which form part of the Parliament Buildings National Historic Site of Canada in the National Capital of Ottawa. There are more than 2000 masonry sculptural elements throughout the four buildings. Three of the buildings are in the middle of multi-year rehabilitation projects. Extensive Heritage Documentation is being undertaken to support various activities and conservation teams throughout the interior and exterior of the buildings while also serving as a key posterity records. One of the significant heritage documentation projects is the 3D digitization of the 2000+ heritage character defining sculptural elements. The Heritage Conservation Directorate (HCD) of Public Works and Government Services Canada (PWGSC) was tasked by the Parliamentary Precinct Branch (PPB) of PWGSC to document these character defining elements. The sculptures vary in size from as small as 100mm in width to up to 2 meters in size. This project is in its third year and much has been learned and researched about the most appropriate and efficient means by which to document these elements. Although a methodology was in place to document the sculptures at the inception of the project, it has gone through several iterations in order to improve the gathered data, and in turn incre

Building Information Modeling for Cultural Heritage: The Management of Generative Process for Complex Historical Buildings

Building Information Modeling (BIM) enhances the sharing of information during the traditional process for new construction, but most of the time, it requires high levels of knowledge management for the historical digital model (H-BIM). The innovation in the Digital Cultural Heritage (DCH) domain is supported by the development of Information and Communications Technologies (ICT) and modern tools that are able to transmit morphological characteristics of the buildings in all their uniqueness. The latest research in the field of H-BIM shows a significant emergence of innovative methods and management initiatives for the generation of complex historical elements, leading to the confrontation of the paradigm of regularity (simple geometric shapes) with the new paradigm of complexity (historical building elements). This paper proves the benefits of the BIM for project management of the Centre Block of the Canadian Parliament in Ottawa, Ontario Canada, and shows the results obtained by the introduction of Advanced Modeling Techniques (AMT) during the generative process, reducing time and cost for the creation of the complex architectural and structural elements. The uniqueness of the forms of historical buildings is a real value to be transmitted throughout the building’s lifecycle with high Levels of Detail (LOD). Proper management of geometric primitives and Non-Uniform Rational Basis Spline (NURBS) models have guaranteed the conversion of spatial data (point clouds) from laser scanning and photogrammetry (geometric survey) into parametric applications. This paper explores the generative process of one of the most complex spaces within The Centre Block building of Parliament Hill—Confederation Hall

Recording Earthen Architecture at the Peruvian Andes: the Case of KUÑO Tambo CHURCH'S Historic Wall Paintings

According to UNESCO “Earthen architecture is one of the most original and powerful expressions of our ability to create a built environment with readily available resources. It includes a great variety of structures, ranging from mosques, palaces and granaries, to historic city centres, cultural landscapes and archaeological sites” (WHEAP, 2007). This contribution looks at developing effective methods for recording earthen his

Nine years of in situ soil warming and topography impact the temperature sensitivity and basal respiration rate of the forest floor in a Canadian boreal forest

The forest floor of boreal forest stores large amounts of organic C that may react to a warming climate and increased N deposition. It is therefore crucial to assess the impact of these factors on the temperature sensitivity of this C pool to help predict future soil CO2 emissions from boreal forest soils to the atmosphere. In this study, soil warming (+2–4°C) and canopy N addition (CNA; +0.30–0.35 kg·N·ha-1·yr-1) were replicated along a topographic gradient (upper, back and lower slope) in a boreal forest in Quebec, Canada. After nine years of treatment, the forest floor was collected in each plot, and its organic C composition was characterized through solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. Forest floor samples were incubated at four temperatures (16, 24, 32 and 40°C) and respiration rates (RR) measured to assess the temperature sensitivity of forest floor RR (Q10 = e10k) and basal RR (B). Both soil warming and CNA had no significant effect on forest floor chemistry (e.g., C, N, Ca and Mg content, amount of soil organic matter, pH, chemical functional groups). The NMR analyses did not show evidence of significant changes in the forest floor organic C quality. Nonetheless, a significant effect of soil warming on both the Q10 of RR and B was observed. On average, B was 72% lower and Q10 45% higher in the warmed, versus the control plots. This result implies that forest floor respiration will more strongly react to changes in soil temperature in a future warmer climate. CNA had no significant effect on the measured soil and respiration parameters, and no interaction effects with warming. In contrast, slope position had a significant effect on forest floor organic C quality. Upper slope plots had higher soil alkyl C:O-alkyl C ratios and lower B values than those in the lower slope, across all different treatments. This result likely resulted from a relative decrease in the labile C fraction in the upper slope, characterized by lower moisture levels. Our results point towards higher temperature sensitivity of RR under warmer conditions, accompanied by an overall down-regulation of RR at low temperatures (lower B). Since soil C quantity and quality were unaffected by the nine years of warming, the observed patterns could result from microbial adaptations to warming

Experimental Effects of Injunctive Norms on Simulated Risky Driving Among Teenage Males

Objective: Teenage passengers affect teenage driving performance, possibly by social influence. To examine the effect of social norms on driving behavior, male teenagers were randomly assigned to drive in a simulator with a peer-aged confederate to whom participants were primed to attribute either risk-accepting or risk-averse social norms. It was hypothesized that teenage drivers would engage in more risky driving behavior in the presence of peer passengers than no passengers, and with a risk-accepting compared with a risk-averse passenger. Method: 66 male participants aged 16 to18 years holding a provisional driver license were randomized to drive with a risk-accepting or risk-averse passenger in a simulator. Failure to Stop at a red light and percent Time in Red (light) were measured as primary risk-relevant outcomes of interest at 18 intersections, while driving once alone and once with their assigned passenger. Results: The effect of passenger presence on risky driving was moderated by passenger type for Failed to Stop in a generalized linear mixed model (OR = 1.84, 95% CI [1.19, 2.86], p \u3c .001), and percent Time in Red in a mixed model (B = 7.71, 95% CI [1.54, 13.87], p \u3c .05). Conclusions: Exposure of teenage males to a risk-accepting confederate peer increased teenage males’ risky simulated driving behavior compared with exposure to a risk-averse confederate peer. These results indicate that variability in teenage risky driving could be partially explained by social norms

The landslide story

The catastrophic Wenchuan earthquake induced an unprecedented number of geohazards. The risk of heightened landslide frequency after a quake, with potential secondary effects such as river damming and subsequent floods, needs more focused attention