Barrier Coverage with Non-uniform Lengths to Minimize Aggregate Movements

Given a line segment I=[0,L], the so-called barrier, and a set of n sensors with varying ranges positioned on the line containing I, the barrier coverage problem is to move the sensors so that they cover I, while minimising the total movement. In the case when all the sensors have the same radius the problem can be solved in O(n log n) time (Andrews and Wang, Algorithmica 2017). If the sensors have different radii the problem is known to be NP-hard to approximate within a constant factor (Czyzowicz et al., ADHOC-NOW 2009). We strengthen this result and prove that no polynomial time rho^{1-epsilon}-approximation algorithm exists unless P=NP, where rho is the ratio between the largest radius and the smallest radius. Even when we restrict the number of sensors that are allowed to move by a parameter k, the problem turns out to be W[1]-hard. On the positive side we show that a ((2+epsilon)rho+2/epsilon)-approximation can be computed in O(n^3/epsilon^2) time and we prove fixed-parameter tractability when parameterized by the total movement assuming all numbers in the input are integers

Investigations on two classes of covering problems

Covering problems fall within the broader category of facility location, a branch of combinatorial optimization concerned with the optimal placement of service facilities in some geometric space. This thesis considers two classes of covering problems. The first, Covering with Variable Capacities (CVC), was introduced in [1] and adds a notion of capacity to the classical Uncapacitated Facility Location problem. That is, each facility has a fixed maximum quantity of clients it can serve. The objective of each variant of CVC is either to serve all clients, the greatest number of clients possible, or all clients using the least number of facilities possible. We provide approximation algorithms, and in a few select cases, optimal algorithms, for all three variants of CVC. The second class of covering problems is barrier coverage. When the purpose of coverage is surveillance rather than service, a cost effective approach to the problem of intruder detection is to place sensors along the boundary, or barrier, of the surveilled region. A barrier coverage is complete when any intrusion is sure to be detected by some sensor. We limit our consideration of barrier coverage to the one-dimensional case, where the region is a line segment. Sensors are themselves line segments, whose span forms a detection range. The objective of barrier coverage as considered here is to form a complete barrier coverage while minimizing the total movement cost, the sum of the weighted distances moved by each sensor in the solution. We show that, by assuming the sensors lie in initial positions where their detection ranges are disjoint from the barrier, one-dimensional barrier coverage can be solved with an FPTAS. Along the way to developing the FPTAS, we give a fast, simple 2-approximation algorithm for weighted disjoint barrier coverage

Script-based design toolkit for digitally fabricated concrete applied to terrain-responsive retaining wall design

The potential of digitally fabricated concrete (DFC) to produce terrain responsive designs has not been thoroughly investigated. Existing research indicates diverse benefits of DFC, such as the rapid fabrication of customized geometries. This research clarifies the advantages and design processes involved in creating site-specific DFC structures. Existing literature is analyzed to provide an overview of fabrication methods and their impacts and constraints on design. Parametric scripting is used to develop an interactive toolkit that integrates aesthetic, structural, and fabrication considerations into the design process. This toolkit specifically focuses on unreinforced retaining walls with interchangeable modules for terrain analysis, wall form generation, structural analysis, and fabrication analysis. The toolkit provides valuable feedback, such as identifying optimum wall proportions, and enables rapid design explorations. The findings affirm the value of exploratory design tools in managing fabrication complexities. Additionally, by recreating an existing amphitheater, the research indicates that DFC can create site-specific geometries that draw from the surrounding terrain

A study of sensor movement and selection strategies for strong barrier coverage

Intruder detection and border surveillance are some of the many applications of sensor networks. In these applications, sensors are deployed along the perimeter of a protected area such that no intruder can cross the perimeter without being detected. The arrangement of sensors for this purpose is referred to as the barrier coverage problem in sensor networks. A primary question centering such a problem is: How to achieve barrier coverage? On the other hand, sensor nodes are usually battery-powered and have limited energy. It is critical to design energy-efficient barrier construction schemes while satisfying the coverage requirement. First, we studied how to achieve strong barrier coverage with mobile sensors. We leverage the mobility of sensors and relocate them to designated destinations to form a strong horizontal barrier after the random deployment. Algorithms were proposed to calculate the optimal relocating destinations such that the maximum moving distance of sensors is minimized. Depending on the number of sensors on the final barrier, two problems were investigated: (1) constructing a barrier with the minimum number of sensors on the final barrier, and (2) constructing a barrier with any number of sensors on the final barrier. For both problems, we optimized the barrier location instead of fixing it a priori as other works. We proposed algorithms which first identify a set of discrete candidates for the barrier location, then check the candidates iteratively. Both problems could be solved in polynomial time. Second, we investigated how to achieve strong barrier coverage by selectively activating randomly deployed static sensors. We aimed to select the minimum number of sensors to be active to achieve barrier coverage under a practical probabilistic model. The system false alarm probability and detection probability were jointly considered, and a (P_D^{min}, P_F^{max})-barrier coverage was defined where P_D^{min} is the minimum system detection probability and P_F^{max} is the maximum system false alarm probability. Our analysis showed that with the constraint on the system false alarm probability, the number of active sensors affects the detection capability of sensors, which would bring new challenges to the min-num sensor selection problem. We proposed an iterative framework to solve the sensor selection problem under the probabilistic model. Depending on whether the decision fusion was applied, different detection capability evaluation methods were used in the iterative framework. Finally, we studied how to achieve strong barrier coverage in a hybrid network with a mix of mobile and static sensors. A two-step deployment strategy was adopted where static sensors are first randomly deployed, and then mobile sensors are deployed to merge the coverage gap left by the static sensors. We aimed to find the proper coverage gaps to deploy mobile sensors such that (P_D^{min}, P_F^{max})-barrier coverage is achieved, and the total cost of the barrier is minimized. Under the probabilistic model, we solved the problem by iteratively trying multiple assumptions of the number of active sensors, and obtained the min-cost deployment strategy with the help of graph algorithms

Performance of strip seals in Iowa bridges: pilot study

A pilot study was conducted on the premature failures of neoprene strip seals in expansion joints in Iowa bridges. In a relatively large number of bridges, strip seals have pulled out of the steel extrusions or otherwise failed well before the expected life span of the seal. The most serious consequence of a strip seal failure is damage to the bridge substructure due to salt, water, and debris interacting with the substructure. A literature review was performed. Manufacturers\u27 specifications and recommendations, practices in the states bordering Iowa, and Iowa DOT design and installation guidelines were reviewed. Iowa DOT bridge databases were analyzed. A national survey was conducted on the use and performance of strip seals. With guidance from the Iowa DOT, twelve in-service bridges with strip seal expansion joints were selected for detailed investigation. Effective bridge temperatures and corresponding expansion joint openings were measured, DOT inspection reports were reviewed, and likely cause(s) of premature failures of strip seals were proposed. Experimental results show that for a majority of these serious failures (all in concrete girder bridges), the joint opening at 0°F predicted by the Iowa DOT design equations, the joint opening at 0°F extrapolated from the experimental data, or both, are larger than the movement rating of the strip seal specified on the bridge plans. Other likely causes of premature failures of seals in the twelve bridges include debris and ice in the seal cavity, skew of bridge deck, improper installation, and improper setting of the initial gap

Guidelines for Use of Fabrics in Construction and Maintenance of Low-Volume Roads

Porus woven and non-woven fabrics have been used in road construction in Region 6 since 1974. The fabrics have been used: 1) as filters for surface drainage; 2) separation layers to prevent subgrade soil contamination of base layers; 3) subgrade restraining layers for weak subgrades; 4) earth reinforcement to build retaining walls; 5) erosion control, and 6) water-proofing membranes. A reference notebook titled "Fabrics in Construction" is due for release to Region 6 Forests in June 1977. This notebook contains a description of current practices and the state-of~the-art in the use of fabrics in road construction and maintenance. The notebook defines terminology and lists the key factors involved in each usage, and relates the fabric physical and chemical properties to the intended usage. The notebook also contains appropriate technical literature, manufacturers' literature and cost data on the known available fabrics. The report highlights the contents of the reference book and discusses the current knowledge for the use of fabrics in low-volume road construction and maintenance. Present and projected uses of the fabric and the most significant physical properties related to these uses are discussed. Probable future uses and the areas of greatest need for technical knowledge and experience are outlined

An indole trimer: synthesis, self-assembly and applications

The organic semiconductor, the indole -5- carboxylic acid asymmetric trimer (ICAT), was chemically synthesised using a new procedure. Self- assembly of ICAT in solution, produced narrowly dispersed discotic nanoparticles that are stable in solution and transferable between surfaces. Highly ordered ICAT bulk molecular and nanoparticle thin films were produced through controlled assembly of ICAT at the solution /solid interface, using glass substrates functionalised with a variety of self assembled monolayers (SAMs). Two films, in particular, on the hydroxyl and the amine -functionalised substrates had extremely well ordered microstructures, suitable for device application.An immersion based deposition technique was developed, where gold and SAM - functionalised glass substrates were immersed in ICAT solutions made with solvents with a range of polarities. At short immersion times, bulk or particulate films were deposited, as a function of immersion solvent. Longer immersion times produced size tailored vertically aligned nanorod and nanowire arrays, as a function of immersion solvent. The immersion time also controlled both the rod density and rod orientation on the substrates. The results were interpreted in terms of heterogeneous nucleation and subsequent growth. Solvophobic forces induced homogeneous nucleation rather than heterogeneous nucleation, in the immersion systems with water and hydrocarbon based immersion solvents. Aligned nanorods and nanowires were assembled on gold and hydroxyl -functionalised glass substrates when polar aprotic immersion solvents were used. There was no obvious correlation between nanostructure dimensions and solvent polarity in these experiments. This is the first time vertically aligned nanorod arrays have been fabricated with small organic functional molecules, through a solution based technique (non -template).Solution based deposition techniques developed here were used to deposit ICAT onto field effect transistors (FETs), resulting in devices with a range of ICAT film morphologies. Single crystal devices were also produced where the ICAT crystal bridged the active channel, defined as the gap between the source and drain electrodes. Several chips, with over 20 FETs on each chip, with each ICAT film morphology type, were fabricated. Selected chips had consistent, reproducible current/voltage (IV) outputs that varied within « one order of magnitude, when probed on all areas. The devices produced n and p -type unipolar activity and the onset of ambipolar activity in ambient conditions, at low voltage probing ranges. Carrier type was dependent on the film morphology. Device lifetime was dependent on film thickness

Use of geotextiles with enhanced lateral drainage in roads over expansive clays

textExpansive clays are very abundant across the central United States in general and in the state of Texas in particular damages induced by expansive clays have been reported to reach several billions of dollars per year. Volume changes in expansive soils due to change in their moisture content varies has caused significant cracking in roads and has resulted in costly maintenance projects over the lifetime of these roads. In Texas, expansive soils have been often treated with lime stabilization, which is not always possible, and in some cases by removing and replacing them with nonexpansive soils, which can be very costly. Recently, geosynthetic reinforcements have been incorporated in roads founded on expansive clays to make the structure stiffer and less prone to cracking. A new geotextile, which is capable of providing enhanced lateral drainage through capillarity has been recently develop. Facilitating moisture redistribution would be a feasible approach for roads on expansive clays as they may lead uniform vertical displacements resulting in minimized cracking in the asphalt layer. Eight test sections with different geotextiles were constructed on State Highway 21 in Bastrop, Texas. The road is founded on expansive clays. A number of geotextiles, including one with enhanced lateral drainage capabilities, were incorporated to 500 feet long test sections. All sections were equipped with sensors to monitor moisture beneath the geotextiles and were periodically surveyed to document pavement distresses. Results showed that the geotextile with enhanced lateral drainage was able to maintain a uniform moisture content along the length of the soil in contact with this geosynthetic. Condition surveys showed that the geotextile with enhanced lateral drainage prevented cracking in the portion of the pavement above it. As expected, cracks often developed in areas of the pavement section beyond the extent of the geotextile. This suggested that the geotextile was capable of providing enhanced lateral drainage, although placement of the geotextile over the full width of the road (and not only under the shoulder) would be necessary to minimize the development of longitudinal cracks. In conclusion, the geotextile with enhanced lateral drainage can deal with pavements on expansive clays by improving the pavements long-term performance.Civil, Architectural, and Environmental Engineerin

Request for proposals final with addendum 1

The purpose of this Request for Proposals (RFP) is to select a Proposer to perform the Project services described in this RFP. SCDOT desires that this Project be constructed in a very efficient and timely manner. This proposal is for a design-build project for a Closed and Load Restricted Bridge Package for Abbeville, Greenwood, Laurens, McCormick, Newberry, and Saluda Counties