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关键词： Social networking (online)   Sports   Blogs   Frequency measurement   Computer science   Benchmark testing   Time measurement   Online local community   query attributes   temporal topical activeness  

摘要： Almost all of the existing approaches to determining online local community are typically deliberated like-minded users who have similar topical interests. However, such methodologies overlook the prospective temporality of users' interests as well as users' degree of topical activeness. As a result, the consequential communities might have extremely lower active users. This research investigates how online social users' behaviors and topical activeness vary over time and how these parameters can be employed in order to improve the quality of the detected local community. For a given input query, consisting a query node (user) and a set of attributes, this research intends to find densely-connected community in which community members are temporally similar in terms of their activities related to the query attributes. To address the proposed problem, we develop a temporal activity biased weight model which gives higher weight to users' recent activities and develop an algorithm to search an effective community. The effectiveness of the proposed methodology is justified using four benchmark datasets and compared with four other baseline methods. Experimental results demonstrate that our proposed framework yields better outcomes than the baseline methods for all four benchmark datasets.

关键词： Radiometry   Cameras   Algorithms   Federations   Light   Geometry   Sensors   Computer science   Mathematics  

关键词： Design   Computer science   Energy   Industrial engineering   Materials science   Mathematics   Mechanics   Physics   Robotics  

摘要： Friction Bit Joining (FBJ) is a new technology that can be used to join dissimilar materials together. This ability makes it a good candidate for creating lightweight structures for the automotive industry by combining lightweight materials such as aluminum to stronger materials like advanced high-strength steels. The automotive industry is putting significant effort into interest in reducing vehicle structure weight to increase fuel efficiency and reduce greenhouse gas emissions. Joining of dissimilar materials is a challenge they face in the light weighting the body of the vehicle. The purpose of the current research is to employ FBJ in the joining of a very challenging material combination: GA DP 1180 to AA 7085-T71. In accomplishing this purpose, the goal is to move FBJ toward a more production ready process by better understanding the effects of tooling, bit design, and process parameters on joint strength and reliability as they relate to load profiles captured during the joining process. It was found that the joint strength variation was influenced strongly by the hardness and the geometric consistency of the consumable bits. Bit hardness below 45 HRC led to joint strength that was less than the required specification (5kN in lap shear tension, and 1.5kN in cross-tension and T-peel). Variation in bit height and diameter also led to excessive scatter in joint strength values, where it was not possible to meet the standard for 10 consecutive specimens (for each of the three tests). Implementation of high-speed data acquisition (1000Hz) enabled the capture of load curve profiles generated during FBJ. Load curve profiles were correlated with destructive testing results to discover the impact of process parameter combinations. Analysis of load curve profiles led to improvements in parameter selections of spindle speeds (revolutions per minute) and spindle feed-rates (inches per minute). Process parameters of 5000 RPM and 15 IPM reduced variation in load-curve prof

关键词： Computer science   Transportation  

摘要： This work investigates the significance of choosing appropriate recurrent neural networks (RNNs) architecture for a spatiotemporal next location prediction framework. Dockless shared micro-mobility sharing programs provide spatial trajectory data that entails essential information for city planners and developers. The study compares (i) the variable-sized geohash tessellation and (ii) two common RNN architectures: Long Short-Term Memory (LSTM) and Gated Recurrent Units (GRU), using bike/scooter location data for Washington DC, USA. LSTM and GRU networks are used for modeling and incorporating information from spatial neighbors into the model. The study suggests that the LSTM model yields slightly better performance than the GRU model based on the same tessellation. However, geohash size might play a significant role in model performance. The study highlights the need to explore hyperparameter tuning, multiple spatial partitioning techniques especially with the Google S2 library, and more trip data for improving the prediction performance in neural network models.

关键词： Diodes   Control algorithms   Cooling   Potassium   Lasers   Optics   Magnetic fields   Syrups & sweeteners   Computer science   Electromagnetics   Food science   Physics  

摘要： Experiments to study the alternating current magneto-optical trap (AC-MOT) of 39K atoms and then to study the 39K Rydberg atoms produced in the AC-MOT were carried out. The laser cooling and trapping process was operated using the closed cycle between the 4 2S1/2(F = 2,mF = +2) ground state and the 4 2P3/2 (F' 0 = 3, mF' = +3) excited state in the 39K atom. The AC-MOT experiment allowed the trapping magnetic field to be switched off rapidly within ∼ 20 µs. In this experiment, the 39K atoms were trapped for 600 µs and then the trapping magnetic field was switched off for another 600 µs. To completely switch off the AC-MOT, an optical chopper was used to block the optical molasses laser beams during the trapping magnetic field off period. This alternately on-off AC-MOT setup produced a cold 39K trap with a vertical radius of ∼ 1.67 mm and a horizontal radius of ∼ 1.79 mm. The number of trapped atoms in the steady state was (12 ± 2) × 106 atoms corresponding to a trap density of (52 ± 8) × 107 atoms/cm3 . The trap temperature was estimated to be between 146 − 725 µK. During the AC-MOT off period, the 39K Rydberg atoms were produced in the cold 39K trap by a step-wise method. A 770 nm laser beam was used to produce the 4 2S1/2 (F = 1)→ 4 2P1/2 (F' = 2) transition and then a blue laser beam (∼ 454 nm) was used to produce the Rydberg atoms via the 4 2P1/2 (F' = 2)→ nS, nD transitions. The 39K+ ions were produced by collisional ionization of the Rydberg atoms and a channel electron multiplier was used to detect these ions. The Rydberg spectra of the 62D − 71S states was then obtained. These results suggested for any given pair of the nD state and (n + 2) S state, excitation to the nD state was more probable than to the (n + 2) S state. The Rydberg spectra of the 120D − 131S states were also obtained. In these results, the dipole forbidden 4 2P1/2 → nP transitions were also seen due to the influence of stray external electric fields in the AC-MOT region. An attempt to elimi

关键词： Probability   Similarity measures   Algorithms   Clustering   Survival analysis   Decision making   Medical research   Computer science   Mathematics  

摘要： Clustering is an important analytical technique that has proven to affect human life positively through its application in cancer research, market segmentation, city planning etc. In this time of growing technological systems, mixed data has seen another face of longitudinal, directional and functional attributes which is worth paying attention to and analyzing. Previous research works on clustering relied largely on the inverse weight technique and B-spline in smoothing data and assessing the performance of various clustering algorithms. In 1971, Gower proposed a method of clustering for mixed variable types which has been extended to include functional and directional variables by Hendrickson (2014). In this study, we will do a comparative analysis of the performance of the hierarchical clustering mechanism using a simulated Functional data with mixed structure. We will adopt the Fourier basis smoothing procedure and use the Rand index (Rand 1971) and adjusted Rand index for the comparison of the various clustering algorithms.

关键词： Computer science   Artificial intelligence  

摘要： When working in an unfamiliar online environment, it can be helpful to have an observer that can intervene and guide a user toward a desirable outcome while avoiding undesirable outcomes or frustration. The Intervention Problem is deciding when to intervene in order to help a user. The Intervention Problem is similar to, but distinct from, Plan Recognition because the observer must not only recognize the intended goals of a user but also when to intervene to help the user when necessary. In this dissertation, we formalize a family of intervention problems to address two sub-problems: (1) The Intervention Recognition Problem, and (2) The Intervention Recovery Problem. The Intervention Recognition Problem views the environment as a state transition system where an agent (or a human user), in order to achieve a desirable outcome, executes actions that change the environment from one state to the next. Some states in the environment are undesirable and the user does not have the ability to recognize them and the intervening agent wants to help the user in the environment avoid the undesirable state. In this dissertation, we model the environment as a classical planning problem and discuss three intervention models to address the Intervention Recognition Problem. The three models address different dimensions of the Intervention Recognition Problem, specifically the actors in the environment, information hidden from the intervening agent, type of observations and noise in the observations. The first model: Intervention by Recognizing Actions Enabling Multiple Undesirable Consequences, is motivated by a study where we observed how home computer users practice cyber-security and take action to unwittingly put their online safety at risk. The model is defined for an environment where three agents: the user, the attacker and the intervening agent are present. The intervening agent helps the user reach a desirable goal that is hidden from the intervening agent by recognizing c

关键词： Computer science   Artificial intelligence   Information technology  

摘要： A Neural Algorithm of Artistic Style introduced an artificial system to create artistic images. It does so by generating a set of feature maps from a content image and a style image. These feature maps are used to generate a loss, which is applied iteratively to a noisy image via gradient descent. This process results in the generated image having features which represent that of the target content and the target style images. The goal of this project is to explore the original research decisions, and explicitly document the tradeoffs being made. The original research used the Visual Geometry Group’s 19 weight-layer model. Many properties of this method were not fully documented - the optimization method is not specified (only broadly referred to as gradient descent), the architecture is altered to “improve gradient flow” without documenting how it was improved, no other models are evaluated, and many properties of the gradient descent process were not explored. This project aims to explore additional models, document various methods of gradient descent, explain characteristics of the loss, and propose solutions to improve the gradient flow.

关键词： Robotics   Computer science   Systems science  

摘要： In situations as diverse as search and rescue, exploration, or war, communications among actors is vital to accomplish a mission. Wireless robotic routers that physically reposition themselves have been proposed as a means of preventing network partitions from occurring. However, it is impossible to prevent network partition in all cases, and so methods that adapt to network partition are of paramount importance. This dissertation proposes and compares different control strategies aimed at solving the network partition problem by tasking individual mobile robots as message couriers between network partitions. To support this work, a model of the universe is presented and justified, and used as the basis for a new simulator written for this thesis. The control strategies are described and implemented, and their performance is measured using the simulator. Finally, further avenues of research are discussed.

关键词： Computer science   Automotive engineering   Transportation  

摘要： Traffic state estimation is a fundamental task of Intelligent Transportation Systems. Recent advances in sensor technology and emerging computer and vehicular communications paradigms have brought the task of estimating traffic state parameters in real-time within reach. This has led to the main research question of this thesis: Can a vehicle accurately estimate traffic parameters using onboard resources shared through CV technology in a lightweight manner without utilizing centralized or roadside infrastructure? In 1954 Wardrop and Charlesworth proposed the Moving Observer method to measure traffic parameters based on an observed number of vehicle passes. We start by proposing methods for detecting vehicle passes using both radar and V2X as a well as with V2X only. Next, a modernization of the Moving Observer method, called the MO1 method, using the capabilities of modern vehicles is proposed which mitigates some of the limitations of the original method. The results show our method is able to provide estimates comparable to stationary observer methods, even in low flow scenarios. The MO2 method also utilizes two vehicles traveling in the same direction to determine a density between the two vehicles. Again, the results show this method provides estimates comparable to stationary observer methods, even in low flow scenarios. The MO3 method is similar to the MO2 method; however, here the two vehicles travel in oncoming traffic. In doing so, the vehicles’ relative velocity is large, leading us to hypothesize that the method will work well in urban traffic. The results for the MO3 method in urban traffic did not meet our expectations, which inspired us to develop the MO3-Flow method. The MO3-Flow method aggregates the counts of multiple vehicles to determine flow. The MO3-Flow method requires additional roadside infrastructure. To remove this need, a Virtual Road Side Unit architecture is proposed. This architecture uses vehicles on the roadway to act in place of road