Direct QR factorizations for tall-and-skinny matrices in MapReduce architectures

The QR factorization and the SVD are two fundamental matrix decompositions with applications throughout scientific computing and data analysis. For matrices with many more rows than columns, so-called "tall-and-skinny matrices," there is a numerically stable, efficient, communication-avoiding algorithm for computing the QR factorization. It has been used in traditional high performance computing and grid computing environments. For MapReduce environments, existing methods to compute the QR decomposition use a numerically unstable approach that relies on indirectly computing the Q factor. In the best case, these methods require only two passes over the data. In this paper, we describe how to compute a stable tall-and-skinny QR factorization on a MapReduce architecture in only slightly more than 2 passes over the data. We can compute the SVD with only a small change and no difference in performance. We present a performance comparison between our new direct TSQR method, a standard unstable implementation for MapReduce (Cholesky QR), and the classic stable algorithm implemented for MapReduce (Householder QR). We find that our new stable method has a large performance advantage over the Householder QR method. This holds both in a theoretical performance model as well as in an actual implementation

Re-Envisioning Course-Embedded Programs at the Graduate Level: A Tutor's Experience in a Doctoral, Translingual Marketing Course

We were halfway through our Summer 2014, PhD-level, required University of Houston,2 Bauer College of Business class, MARK 8397: Communicating Academic Research, when Carol,3 a five-foot tall, thick-skinned, straight-shooting, endowed chair and Marketing professor explained my role in her course as “hand holding.” I raised my eyebrow and waited for her to continue. “You know, confidence building,” she continued. I felt slightly better. Then she said, “Academic writing is confusing for students because they don’t know which way to go. They might know when and why they need to make changes, but they don’t really know how to do it.” This was better. Carol’s idea of me as a guide for students through the “how” of academic writing was something I felt matched my own understanding of my role in the course.University Writing Cente

The watering of tall trees - Embolization and recovery

We can propound a thermo-mechanical understanding of the ascent of sap to the top of tall trees thanks to a comparison between experiments associated with the cohesion-tension theory and the disjoining pressure concept for liquid thin-films. When a segment of xylem is tight-filled with crude sap, the liquid pressure can be negative although the pressure in embolized vessels remains positive. Examples are given that illustrate how embolized vessels can be refilled and why the ascent of sap is possible even in the tallest trees avoiding the problem due to cavitation. However, the maximum height of trees is limited by the stability domain of liquid thin-films.Comment: Extended introduction and additive comments removed from the Journal of Theoretical Biology.22 page

Integration and Segmentation Conflict During Ensemble Coding of Aspect Ratio

The visual system often integrates information that goes together . Once information has been integrated, summary information (e.g., average emotion or average size) can be extracted; this occurs during ensemble coding. Integration thus allows for fast and efficient generalizations about sets to be made. In contrast, the visual system sometimes segments input that does not go together. For example, the perception of objects can be exaggerated away from natural category boundaries (e.g., a perfect circle is a category boundary; it is neither flat nor tall ). Segmentation allows the visual system to make quick categorical distinctions. Much of the time, integration and segmentation work in parallel, and they have most often been studied in isolation. However, investigating how these two processes operate together, and potentially even conflict, was the purpose of this dissertation. I examined the ensemble coding of aspect ratio, which is a visual feature roughly equivalent to tallness/flatness . Aspect ratio has a category boundary (e.g., a circle or square), and the perception of aspect ratio tends to be exaggerated -segmented - away from that boundary. Thus, I predicted that observers\u27 ability to integrate aspect ratio information that spanned the category boundary would be disrupted, since in those instances, integration and segmentation would be at odds. To test this prediction, observers were asked about the average aspect ratio of a set of ellipses. In two experiments, observers were less sensitive to the mean of sets that included both tall and flat ellipses, compared to sets that only included tall or flat ellipses. A third experiment confirmed that segmentation perceptually distorted the appearance of ellipses near the category boundary away from that boundary; shapes were perceived to be more extreme than they actually were. Segmentation thus made sets that included both flat and tall ellipses appear more heterogeneous than they really were, which disrupted ensemble coding. In general, these experiments provide a deeper understanding of how the visual system summarizes large sets of information, by investigating how integration interacts with, and even conflicts with, segmentation

Influence of building neighbors on wind flow around a tall building

This thesis focuses on how building neighbors influence wind flow around a tall building. The wake dynamics and flow structures around a tall building are first explored using Large Eddy Simulations (LES). Following this, wake topology, flow structures, and vortical structures are investigated when a small building is placed downstream and upstream of a tall building. The wake and flow structures formed from the building neighbors’ effects around the tall building were compared with the wake features and flow structures observed for the single tall building case. The study of the wake was first investigated when a building neighbor (small building) was present downstream of a tall building. The influence a small building has on wind flow around the tall building was investigated by examining how wake and flow structures change when a small building was introduced. A weaker downwash flow shown by the decrease in vorticity was observed as opposed to when the tall building was isolated. This is primarily due to the presence of the small building downstream which subsequently reduced the wake effects from the tall building. Pedestrians will therefore experience better comfort at the wake region as opposed to when the tall building was isolated. Different flow structures were observed. First, a reverse-c shaped type of vortex was formed at the near wake which develops into hairpin type of vortices at the far wake. When upwash, downwash, and shear layers interact, hairpin vortices form, creating an increase in wake instabilities. A horseshoe vortex forms in the wake, with its legs extending into the wake, interacting with the wake structure formed behind the buildings and having an immediate effect on wake dynamics. At the windward face of the small building, which lies in the aerodynamic wake of the tall building, the mean pressure coefficient decreased even more, reaching ̅̅̅ ≈ 0.07. The progressive decrease in mean pressure coefficient (82.5%) shows how the mean wind load reduces downstream due to the presence of the small building downstream. This further shows how aerodynamic wake effects decrease considerably more quickly. [...

Super Tall Timber: design research for the next generation of natural structure

This research project aspires to make truly tall timber buildings a reality. Through a combination of theoretical design and physical testing this research demonstrates the viability of timber buildings at much greater heights than has previously been possible. By pushing the limits of theoretical designs into the realms of the supertall, sometimes beyond that which is feasible using current materials and construction technologies, this research also sets out the requirements for the next generation of engineered plant-based materials. The research is a collaboration between academics, practicing architects and practicing structural engineers. The approach is research through design, and design through research. Timber towers are designed well beyond exist ing heights, and analysed to understand how they stand up and which areas are most critical for further research. By bringing highly regarded architectural and structural designers together with the research capabilities of a leading university, this project creates a precedent-setting model for interdisciplinary engagement within and between the design and research communities. By coupling exemplary design in timber a university’s research capacity, the project represents a real opportunity for transform ational change in the design of tall timber buildings. Essential details and connections are determined and ‘unknowns’ with respect to material and structural performance are identified. A programme of testing to investigate these unknowns and validate the design approaches is carried out at the university. Outcomes of the test programme and new insights are fed back into the design process. The results show that tall timber towers are feasible, with substantial but surmountable questions outstanding. By providing thought provoking yet credible solutions for the design of tall timber buildings and exceeding current limits, the project can inspire the design community to think beyond the status quo and embrace the possibilities offered by timber construction.The work forms part of a research study conceived and led by Cambridge University with input from PLP Architecture and Smith and Wallwork Engineers. Funding for this research is in part provided by the EPSRC under grant EP/M01679X/1

Testing C4.5 Algorithm Using Rapid Miner Applications In Determining Customer Satisfaction Levels

Data mining is a series of processes to extract added value in the form of information that has not been known manually from a database. The resulting information is obtained by extracting and recognizing important or interesting patterns from the data contained in the database.  One part of the service of an agency is the service to customers, customers or those related to certain services. The quality of service is assessed by what has been done and how to treat from those who serve, some provisions used to ensure service optimization are Confiden, Integrity, Pride and Passion with the main purpose or output is Customer Satisfaction. The process of Forming a Pattern of Satisfaction Level by Utilizing the C4.5 Algorithm Penelitain process is carried out by data collection, testing with applications, exposure of pattern results or Knowledge. Pola yang terbentuk after the extraction is 1.Integrity = low: quite satisfied {very satisfied=0, quite satisfied=3}Integrity = tall, Passion = low: quite satisfied {very satisfied =0, quite satisfied =2}, Passion = tall: very satisfied {very satisfied =11, quite satisfied =0}

Effects of endophyte infection and methyl bromide on surface-dwelling and edaphic arthropods in tall fescue

Tall fescue is a common, cool-season pasture grass in the United States. When infected with the endophytic fungus, Acremonium coenophialum, it is associated with tall fescue toxicosis. Studies have been conducted to determine the effects of this grass/endophyte interaction on mammals as well as herbivorous arthropods. There has been little previous work done to determine the effects of the interaction on predators and decomposers. The objective of this study was to determine whether the presence of Acremonium coenophialum changed the community structure and population dynamics of mesoarthropods in tall fescue fields. The effects of previous methyl bromide treatment in half of the fields were also examined. Collembola (springtails), Acari (mites), and Carabidae (ground beetles) were collected with pitfall traps for at least six weeks per season for one year. An alcohol mixture was used as a preservative in the field. Pitfall contents were collected twice weekly. Soil cores were taken once a month and arthropods were extracted either with a Crossley-Blair high-gradient soil extraction or by means of a heptane flotation technique. The effects of endophyte-infected tall fescue on Collembola were species-specific. Sphaeridia pumilus, Sminthurus fitchi, Sminthurinus henshawi, and Isotoma viridis often had significantly higher populations in endophyte-infected (E+) tall fescue fields. Homidia soda and Pseudosinella violenta were more abundant in endophyte free (E-) fields. Lepidocyrtus cinereus had similar population densities in both E-i- and E- fields. Association measures for Collembola indicated that E-t- tall fescue selected a particular community composition. Carabids were collected in relatively low numbers in all fields and did not seem to be affected by the presence of the endophyte. Acari were more abundant in E- fields and therefore may have been adversely affected by the endophyte. The effects of previous methyl bromide treatment were more apparent on truly edaphic species such as Parajapyx isabellae and Epilhommania sp. However, Isotoma viridis, S. henshawi, S. fitchi, Sminthurinus elegans, and Sphaeridia pumilus were most abundant in methyl bromide treated (MB+) fields. Lepidocyrtus cinereus and P. violenta were more common in fields not treated with methyl bromide (MB-). Homidia soda showed no preference for MB+ or MB- fields. Carabid populations were also lower in MB+ fields. Groups of Acari acted differently with respect to methyl bromide. Galumna sp. and other Oribatida populations were higher in MB+ fields, but Epilohmannia sp. was higher in MB- fields. Additional studies on mesofauna in E+ and E- tall fescues would benefit from monitoring the alkaloid concentrations in the field. Together the information could bring about a better understanding of how the alkaloids produced by the grass/endophyte interaction affect organisms within the field. A different method of soil core extraction should be used to give a better estimate of the soil fauna present

Global observational diagnosis of soil moisture control on the land surface energy balance

An understanding of where and how strongly the surface energy budget is constrained by soil moisture is hindered by a lack of large-scale observations, and this contributes to uncertainty in climate models. Here we present a new approach combining satellite observations of land surface temperature and rainfall.We derive a Relative Warming Rate (RWR) diagnostic, which is a measure of how rapidly the land warms relative to the overlying atmosphere during 10 day dry spells. In our dry spell composites, 73% of the land surface between 60°S and 60°N warms faster than the atmosphere, indicating water-stressed conditions, and increases in sensible heat. Higher RWRs are found for shorter vegetation and bare soil than for tall, deep-rooted vegetation, due to differences in aerodynamic and hydrological properties. We show how the variation of RWR with antecedent rainfall helps to identify different evaporative regimes in the major nonpolar climate zones