Performance evaluation of inverted pavement structures

Pavements are an integral part of modern transportation infrastructure. Growing pavement networks, diminishing resources, and climate change create a need for higher performing, more economical, and more sustainable pavement designs. Inverted base pavements (“inverted pavement” or IBP) is the term for a flexible pavement design philosophy different from conventional designs used in the United States. Inverted pavements maximize the performance of their constituent materials by taking advantage of their inherent properties. In IBP, the asphalt concrete surface layer is underlain by an unbound aggregate base layer, followed by a bound layer of stabilized aggregate subbase. This arrangement provides greater confining stress to the base course, resulting in a stiffer, more resilient structure. The improved performance of inverted pavement can reduce the thickness of the entire structure as well as the surface layer when compared to conventional pavement structures. Inverted base pavements may provide a solution to poor-performing, expensive, and unsustainable pavements. The first goal of this thesis is to explore the long-term performance of inverted pavements in the United States. While they have a longer history of use in other countries, inverted pavements have not been widely accepted in the United States. After a review of relevant literature, a field evaluation was conducted on two test sections of inverted pavement in Georgia. Falling weight deflectometer (FWD) measurements and a surface distress survey were conducted on the sections at 21 and 13 years of age, respectively. Results showed that the test sections performed better than conventional pavements. FWD data revealed that inverted sections exhibited greater structural stiffness and resistance to deformation over the life of the roadways. Material properties backcalculated from FWD data provided useful parameters for the modeling effort conducted in this study. The survey of surface distresses showed that inverted pavement sections accumulate less permanent deformation and load-related cracking, indicating superior load distribution and fatigue resistance. The second goal of this research was to examine the suitability of IBP for aircraft traffic. Few previous studies have explored this application. A modeling effort was undertaken using a mechanistic-empirical pavement analysis software to evaluate inverted and conventional pavement under simulated airplane loading. The simulated test sections were designed using material properties and layer dimensions from the literature, the field study in this thesis, and the software default values. The results predicted IBP could bear a significantly greater amount of traffic in every climate tested, when compared to conventional sections designed for the same loading. Furthermore, many inverted designs outperformed conventional pavements despite having thinner cross sections and thinner asphalt concrete layers. This indicates that inverted pavements may provide a cheaper, more sustainable solution for airfield pavements without a decline in performance. These results demonstrate that inverted pavements have a place in the future transportation networks of the United States. Further research is required to provide greater insight into the structures’ response to loading, particularly in varying climates. Additionally, modeling efforts should be refined by considering the stress- and climate-dependent properties of pavement materials. Finally, full-sized field and lab efforts should be undertaken to explore the application of IBP as airfield pavements using modern materials characterization and instrumentation. While a more complete understanding of inverted pavements is needed, this study has confirmed that inverted pavements can improve the performance, economy, and sustainability of our transportation networks.M.S

An efficient closed frequent itemset miner for the MOA stream mining system

Mining itemsets is a central task in data mining, both in the batch and the streaming paradigms. While robust, efficient, and well-tested implementations exist for batch mining, hardly any publicly available equivalent exists for the streaming scenario. The lack of an efficient, usable tool for the task hinders its use by practitioners and makes it difficult to assess new research in the area. To alleviate this situation, we review the algorithms described in the literature, and implement and evaluate the IncMine algorithm by Cheng, Ke, and Ng (2008) for mining frequent closed itemsets from data streams. Our implementation works on top of the MOA (Massive Online Analysis) stream mining framework to ease its use and integration with other stream mining tasks. We provide a PAC-style rigorous analysis of the quality of the output of IncMine as a function of its parameters; this type of analysis is rare in pattern mining algorithms. As a by-product, the analysis shows how one of the user-provided parameters in the original description can be removed entirely while retaining the performance guarantees. Finally, we experimentally confirm both on synthetic and real data the excellent performance of the algorithm, as reported in the original paper, and its ability to handle concept drift.Postprint (published version

Prospects and limitations of full-text index structures in genome analysis

The combination of incessant advances in sequencing technology producing large amounts of data and innovative bioinformatics approaches, designed to cope with this data flood, has led to new interesting results in the life sciences. Given the magnitude of sequence data to be processed, many bioinformatics tools rely on efficient solutions to a variety of complex string problems. These solutions include fast heuristic algorithms and advanced data structures, generally referred to as index structures. Although the importance of index structures is generally known to the bioinformatics community, the design and potency of these data structures, as well as their properties and limitations, are less understood. Moreover, the last decade has seen a boom in the number of variant index structures featuring complex and diverse memory-time trade-offs. This article brings a comprehensive state-of-the-art overview of the most popular index structures and their recently developed variants. Their features, interrelationships, the trade-offs they impose, but also their practical limitations, are explained and compared

SODA: Generating SQL for Business Users

The purpose of data warehouses is to enable business analysts to make better decisions. Over the years the technology has matured and data warehouses have become extremely successful. As a consequence, more and more data has been added to the data warehouses and their schemas have become increasingly complex. These systems still work great in order to generate pre-canned reports. However, with their current complexity, they tend to be a poor match for non tech-savvy business analysts who need answers to ad-hoc queries that were not anticipated. This paper describes the design, implementation, and experience of the SODA system (Search over DAta Warehouse). SODA bridges the gap between the business needs of analysts and the technical complexity of current data warehouses. SODA enables a Google-like search experience for data warehouses by taking keyword queries of business users and automatically generating executable SQL. The key idea is to use a graph pattern matching algorithm that uses the metadata model of the data warehouse. Our results with real data from a global player in the financial services industry show that SODA produces queries with high precision and recall, and makes it much easier for business users to interactively explore highly-complex data warehouses.Comment: VLDB201

Structural and Electrical Investigation of Cobalt-Doped NiOx/Perovskite Interface for Efficient Inverted Solar Cells

Inorganic hole-transporting materials (HTMs) for stable and cheap inverted perovskite-based solar cells are highly desired. In this context, NiOx, with low synthesis temperature, has been employed. However, the low conductivity and the large number of defects limit the boost of the efficiency. An approach to improve the conductivity is metal doping. In this work, we have synthesized cobalt-doped NiOx nanoparticles containing 0.75, 1, 1.25, 2.5, and 5 mol% cobalt (Co) ions to be used for the inverted planar perovskite solar cells. The best efficiency of the devices utilizing the low temperature-deposited Co-doped NiOx HTM obtained a champion photoconversion efficiency of 16.42%, with 0.75 mol% of doping. Interestingly, we demonstrated that the improvement is not from an increase of the conductivity of the NiOx film, but due to the improvement of the perovskite layer morphology. We observe that the Co-doping raises the interfacial recombination of the device but more importantly improves the perovskite morphology, enlarging grain size and reducing the density of bulk defects and the bulk recombination. In the case of 0.75 mol% of doping, the beneficial effects do not just compensate for the deleterious one but increase performance further. Therefore, 0.75 mol% Co doping results in a significant improvement in the performance of NiOx-based inverted planar perovskite solar cells, and represents a good compromise to synthesize, and deposit, the inorganic material at low temperature, without losing the performance, due to the strong impact on the structural properties of the perovskite. This work highlights the importance of the interface from two different points of view, electrical and structural, recognizing the role of a low doping Co concentration, as a key to improve the inverted perovskite-based solar cells’ performance