Online forum thread retrieval using data fusion

Online forums empower people to seek and share information via discussion threads. However, finding threads satisfying a user information need is a daunting task due to information overload. In addition, traditional retrieval techniques do not suit the unique structure of threads because thread retrieval returns threads, whereas traditional retrieval techniques return text messages. A few representations have been proposed to address this problem; and, in some representations aggregating query relevance evidence is an essential step. This thesis proposes several data fusion techniques to aggregate evidence of relevance within and across thread representations. In that regard, this thesis has three contributions. Firstly, this work adapts the Voting Model from the expert finding task to thread retrieval. The adapted Voting Model approaches thread retrieval as a voting process. It ranks a list of messages, then it groups messages based on their parent threads; also, it treats each ranked message as a vote supporting the relevance of its parent thread. To rank parent threads, a data fusion technique aggregates evidence from threads’ ranked messages. Secondly, this study proposes two extensions of the voting model: Top K and Balanced Top K voting models. The Top K model aggregates evidence from only the top K ranked messages from each thread. The Balanced Top K model adds a number of artificial ranked messages to compensate the difference if a thread has less than K ranked messages (a padding step). Experiments with these voting models and thirteen data fusion methods reveal that summing relevance scores of the top K ranked messages from each thread with the padding step outperforms the state of the art on all measures on two datasets. The third contribution of this thesis is a multi-representation thread retrieval using data fusion techniques. In contrast to the Voting Model, data fusion methods were used to fuse several ranked lists of threads instead of a single ranked list of messages. The thread lists were generated by five retrieval methods based on various thread representations; the Voting Model is one of them. The first three methods assume a message to be the unit of indexing, while the latter two assume the title and the concatenation of the thread message texts to be the units of indexing respectively. A thorough evaluation of the performance of data fusion techniques in fusing various combinations of thread representations was conducted. The experimental results show that using the sum of relevance scores or the sum of relevance scores multiplied by the number of retrieving methods to develop multi-representation thread retrieval improves performance and outperforms all individual representation

Instruction fusion and vector processor virtualization for higher throughput simultaneous multithreaded processors

The utilization wall, caused by the breakdown of threshold voltage scaling, hinders performance gains for new generation microprocessors. To alleviate its impact, an instruction fusion technique is first proposed for multiscalar and many-core processors. With instruction fusion, similar copies of an instruction to be run on multiple pipelines or cores are merged into a single copy for simultaneous execution. Instruction fusion applied to vector code enables the processor to idle early pipeline stages and instruction caches at various times during program implementation with minimum performance degradation, while reducing the program size and the required instruction memory bandwidth. Instruction fusion is applied to a MIPS-based dual-core that resembles an ideal multiscalar of degree two. Benchmarking using an FPGA prototype shows a 6-11% reduction in dynamic power dissipation as well as a 17-45% decrease in code size with frequent performance improvements due to higher instruction cache hit rates. The second part of this dissertation deals with vector processors (VPs) which are commonly assigned exclusively to a single thread/core, and are not often performance and energy efficient due to mismatches with the vector needs of individual applications. An easy-to-implement VP virtualization technology is presented to improve the VP in terms of utilization and energy efficiency. The proposed VP virtualization technology, when applied, improves aggregate VP utilization by enabling simultaneous execution of multiple threads of similar or disparate vector lengths on a multithreaded VP. With a vector register file (VRF) virtualization technique invented to dynamically allocate physical vector registers to threads, the virtualization approach improves programmer productivity by providing at run time a distinct physical register name space to each competing thread, thus eliminating the need to solve register name conflicts statically. The virtualization technique is applied to a multithreaded VP prototyped on an FPGA; it supports VP sharing as well as power gating for better energy efficiency. A throughput-driven scheduler is proposed to optimize the virtualized VP’s utilization in dynamic environments where diverse threads are created randomly. Simulations of various low utilization benchmarks show that, with the proposed scheduler and power gating, the virtualized VP yields a larger than 3-fold speedup while the reduction in the total energy consumption approaches 40% compared to the same VP running in the single-threaded mode. The third part of this dissertation focuses on combining the two aforementioned technologies to create an improved VP prototype that is fully virtualized to support thread fusion and dynamic lane-based power-gating (PG). The VP is capable of dynamically triggering thread fusion according to the availability of similar threads in the task queue. Once thread fusion is triggered, every vector instruction issued to the virtualized VP is interpreted as two similar instructions working in two independent virtual spaces, thus doubling the vector instruction issue rate. Based on an accurate power model of the VP prototype, two different policies are proposed to dynamically choose the optimal number of active VP lanes. With the combined effort of VP lane-based PG and thread fusion, compared to a conventional VP without the two proposed capabilities, benchmarking shows that the new prototype yields up to 33.8% energy reduction in addition to 40% runtime improvement, or up to 62.7% reduction in the product of energy and runtime

Online Forum Thread Retrieval using Pseudo Cluster Selection and Voting Techniques

Online forums facilitate knowledge seeking and sharing on the Web. However, the shared knowledge is not fully utilized due to information overload. Thread retrieval is one method to overcome information overload. In this paper, we propose a model that combines two existing approaches: the Pseudo Cluster Selection and the Voting Techniques. In both, a retrieval system first scores a list of messages and then ranks threads by aggregating their scored messages. They differ on what and how to aggregate. The pseudo cluster selection focuses on input, while voting techniques focus on the aggregation method. Our combined models focus on the input and the aggregation methods. The result shows that some combined models are statistically superior to baseline methods.Comment: The original publication is available at http://www.springerlink.com/. arXiv admin note: substantial text overlap with arXiv:1212.533

Bubble Lab Exercise

The cell membrane is a ubiquitous component in mammalian cells which control many vital biological functions. It consists of a phospholipid bilayer with embedded protein molecules which serve to transport molecules between the interior and exterior of the cell. Understanding what makes cell membranes so important and how they function requires concepts from physics, chemistry, and of course biology, but it is difficult to learn and conceptualize the structure and function of membranes due to their nanoscopic size and dynamic nature which can’t be properly appreciated in a static textbook. This activity draws analogies between the chemistry and structure of soap films, which are essentially the inverse of the cell membrane, to create a macroscopic model that illustrates many important concepts in biology. Concepts emphasized include membrane fluidity, flexibility, amphiphilicity, passive/active transport, and membrane fusion/division processes. Using materials entirely available at a grocery store, students explore cell membrane structure and function using the more tangible and accessible soap film