A practitioner's guide for static index pruning

We compare the term- and document-centric static index pruning approaches as described in the literature and investigate their sensitivity to the scoring functions employed during the pruning and actual retrieval stages. © Springer-Verlag Berlin Heidelberg 2009

Systems Theory

Systems Theory has generated a lot of excitement in the last decade. It has also spawned more than its share of pitchmen, enough so that it is in danger of being discredited before its genuine potential in many fields of practice has been fairly tested. Wearing the double halo of Science and Corporate Efficiency conferred by its association with the aerospace industry and the Pentagon, it has been enthusiastically offered to Federal and State governments (Chartrand, 1971; Hoos, 1969 & 1972) as well as private individuals and organizations as a way of solving complex social problems like mass transit, crime, and welfare dependency. As with any situation where expectations are raised (at high cost in contract fees) and then left unfulfilled, the reaction may indict basic ideas and intemperate applications alike. Let us, then, look more closely at the history and logic of systems theory and try to assess its strengths and weaknesses as a guide to social work practice. Remembering Gross\u27 admonition, we must be tolerant of the confusion and error that are part of the ferment of innovative thinking and yet wary of its intoxication. To change the metaphor from food to drink: Getting too high makes one a dangerous driver and an easy mark. This is, after all, the practitioner\u27s special problem. He or she must deal daily with the lives of real people, not imaginative constructs. After a yeasty session with intoxicating ideas, theorists can always sit in the back seat and sing; but the practitioner is the one who has to get behind the wheel and drive safely home

Involving users in the design process: the role of product representations in co-designing

Allowing users to be part of shaping change in new product development can contribute to more successful products. Advances in recent years in digital product representations (such as CAD and rapid prototyping) can potentially offer economic and time-saving benefits to this process. The research in this thesis has generated guidelines to support co-designing activity by exploring the issues of user involvement in the design process, paying particular attention to the use of digital (computer-based) and non-digital product representations to facilitate understanding and communication. The guidelines emerged through empirical research. The first stage of the research explored users' perceptions of physical and emotional product properties through digital and rapid prototyped representations: initial guidelines for Including product representations in co-designing were generated. An Interview study was then conducted to examine the wider issues of user involvement in designing and the use of digital and non-digital product representations from the standpoint of ten practicing - designers. Challenges and barriers to user Involvement were perceived but designers were open-minded to the Idea of digital co-designing. In parallel an audit was undertaken to evaluate product representation technologies for their ability to facilitate co-designing: traditional non-digital methods of sketching and hand-made models were used to develop criteria for this benchmarking. Limitations were found with existing technology and it was apparent that traditional methods (e. g. hand-drawn sketches and models) were better able to facilitate co-designing at this time than digital methods. These findings led to recommendations for future co-designing tools. Co-designing processes were then explored through six practical studies conducted with individuals and small groups of users. Users experimented with designing and making improved handles for a small gardening tool through sketching and day modelling. Design concepts were then taken further into digital media, through 3D scanning, digital CAD images and rapid prototyping and presented back to users for evaluation. Co-designing was also explored through a commercial context with an international packaging manufacturer. Ten users communicated design ideas for improved packaging by triangulation of notes, sketches, discussion and modelling activity. This produced user-led design criteria and commercially valuable concept designs. Important insights were gained into how codesigning may be facilitated within a commercial context and the experiences of the stakeholders. Several pertinent ethical issues such as ownership of ideas, incentives and rewards for user involvement were raised. The thesis concludes with guidelines and recommendations for co-designing, particularly regarding the role of product representations

Nonlinear control strategy for a cost effective myoelectric prosthetic hand

The loss of a limb tremendously impacts the life of the affected individual. In the past decades, researchers have been developing artificial limbs that may return some of the missing functions and cosmetics. However, the development of dexterous mechanisms capable of mimicking the function of the human hand is a complex venture. Even though myoelectric prostheses have advanced, several issues remain to be solved before an artificial limb may be comparable to its human counterpart. Moreover, the high cost of advanced limbs prevents their widespread use among the low-income population. This dissertation presents a strategy for the low-level of control of a cost effective robotic hand for prosthetic applications. The main purpose of this work is to reduce the high cost associated with limb replacement. The presented strategy uses an electromyographic signal classifier, which detects user intent by classifying 4 different wrist movements. This information is supplied as 4 different pre-shapes of the robotic hand to the low-level of control for safely and effectively performing the grasping tasks. Two proof-of-concept prototypes were implemented, consisting on five-finger underactuated hands driven by inexpensive DC motors and equipped with low-cost sensors. To overcome the limitations and nonlinearities of inexpensive components, a multi-stage control methodology was designed for modulating the grasping force based on slippage detection and nonlinear force control. A multi-stage control methodology for modulating the grasping force based on slippage detection and nonlinear force control was designed. The two main stages of the control strategy are the force control stage and the detection stage. The control strategy uses the force control stage to maintain a constant level of force over the object. The results of the experiments performed over this stage showed a rising time of less than 1 second, force overshoot of less than 1 N and steady state error of less than 0.15 N. The detection stage is used to monitor any sliding of the object from the hand. The experiments performed over this stage demonstrated a delay in the slip detection process of less than 200 milliseconds. The initial force, and the amount of force incremented after sliding is detected, were adjusted to reduce object displacement. Experiments were then performed to test the control strategy on situations often encountered in the ADL. The results showed that the control strategy was able to detect the dynamic changes in mass of the object and to successfully adjust the grasping force to prevent the object from dropping. The evaluation of the proposed control strategy suggests that this methodology can overcome the limitation of inexpensive sensors and actuators. Therefore, this control strategy may reduce the cost of current myoelectric prosthesis. We believe that the work presented here is a major step towards the development of a cost effective myoelectric prosthetic hand

Control of large-scale structures with large uncertainties

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 279-300).Performance-based design is a design approach that satisfies motion constraints as its primary goal, and then verifies for strength. The approach is traditionally executed by appropriately sizing stiffnesses, but recently, passive energy dissipation systems have gained popularity. Semi-active and active energy dissipation systems have been shown to outperform purely passive systems, but they are not yet widely accepted in the construction and structural engineering fields. Several factors are impeding the application of semi-active and active damping systems, such as large modeling uncertainties that are inherent to large-scale structures, limited state measurements, lack of mechanically reliable control devices, large power requirements, and the need for robust controllers. In order to enhance acceptability of feedback control systems to civil structures, an integrated control strategy designed for large-scale structures with large parametric uncertainties is proposed. The control strategy comprises a novel controller, as well as a new semi-active mechanical damping device. Specifically, the controller is an adaptive black-box representation that creates and optimizes control laws sequentially during an excitation, with no prior training. The novel feature is its online organization of the input space. The representation only requires limited observations for constructing an efficient representation, which allows control of unknown systems with limited state measurements. The semi-active mechanical device consists of a friction device inspired by a vehicle drum brakes, with a viscous and a stiffness element installed in parallel. Its unique characteristic is its theoretical damping force reaching the order of 100 kN, using a friction mechanism powered with a single 12-volts battery. It is conceived using mechanically reliable technologies, which is a solution to large power requirement and mechanical robustness. The integrated control system is simulated on an existing structure located in Boston, MA, as a replacement to the existing viscous damping system. Simulation results show that the integrated control system can mitigate wind vibrations as well as the current damping strategy, utilizing only one third of devices. In addition, the system created effective control rules for several types of earthquake excitations with no prior training, performing similarly to an optimal controller using full parametric and state knowledge.by Simon Laflamme.Ph.D

Probabilistic Models for Droughts: Applications in Trigger Identification, Predictor Selection and Index Development

The current practice of drought declaration (US Drought Monitor) provides a hard classification of droughts using various hydrologic variables. However, this method does not yield model uncertainty, and is very limited for forecasting upcoming droughts. The primary goal of this thesis is to develop and implement methods that incorporate uncertainty estimation into drought characterization, thereby enabling more informed and better decision making by water users and managers. Probabilistic models using hydrologic variables are developed, yielding new insights into drought characterization enabling fundamental applications in droughts