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Remote Usability Evaluation at a Glance
No full textMuch traditional user interface evaluation is conducted in usability laboratories, where a small number of selected users is directly observed by trained evaluators. However, as the network itself and the remote work setting have become intrinsic parts of usage patterns, evaluators often have limited access to representative users for usability evaluation in the laboratory and the users' work context is difficult or impossible to reproduce in a laboratory setting. These barriers to usability evaluation led to extending the concept of usability evaluation beyond the laboratory, typically using the network itself as a bridge to take interface evaluation to a broad range of users in their natural work settings
Sorting by Bounded Block-Moves
No full textGiven a permutation pi, a block-move is an operation that switches two adjacent blocks of elements in pi. The problem of finding the minimum number of block-moves required to sort pi has applications in computational biology, particularly in the study of genome rearrangements. This paper investigates variants of the problem where bounds are imposed on the lengths of the blocks moved. Algorithms and reduction results are presented for these variants
Response Surface Approximations for Aerodynamic Parameters in High Speed Civil Transport Optimization
No full textA procedure for generating and using polynomial approximations to the range or to the cruise drag components in terms of 29 design variables for a High Speed Civil Transport configuration design is presented. Response surface methodology is used to fit quadratic polynomials to data gathered from a series of numerical analyses of different aircraft designs. Several techniques are employed to minimize the number of required analyses and to maintain accuracy. Approximate analysis techniques are used to find regions of the design space where reasonable aircraft designs could occur and response surface models are built using higher fidelity analysis results of designs in this "reasonable" region. This is a means of using results from advanced CFD methods at the early design stage. Regression analysis and analysis of variance are used to reduce the number of polynomial terms in the response surface model functions. Optimization runs of the aircraft configuration are then carried out with the response surface models and compared to the previous optimization runs without the response surface models. It is shown that considerable reduction of the amount of numerical noise in optimization is achieved with response surface models and the convergence rate is improved. Careful attention was required to keep the accuracy of the models at an acceptable level
Internet Based Real-Time Multiuser Simulation: Ppong!
No full textThere is a growing demand for real-time collaborative applications through the World Wide Web. New techniques are required for real-time applications to perform well in the face of changing network conditions that often include long delays. We present some of the key issues for implementors of real-time web-based applications, including choices on centralized versus distributed control, two versus multiuser considerations, synchronous versus asynchronous message protocols, and simulation divergence. We present an implementation for a web-based version of the classic Pong game, called Ppong!. Ppong! was selected for implementation since it strips to its essentials many components of real-time collaborative simulation. A key feature of Ppong! is implementation of a heuristic for "retarding" a user's view of the simulation to accommodate network delays
WWW Proxy Traffic Characterization with Application to Caching
No full textCharacterizing World Wide Web proxy traffic helps identify parameters that affect caching, capacity planning and simulation studies. In this paper we identify invariants that hold across a collection of ten traces representing traffic seen by caching-proxy servers. The traces were collected from governmental, industry, university, high school, and an online service provider environment, with request rates that range from a few accesses to millions of accesses per hour. We also show that the examined traffic is semi-similar. We explore sources of Web self-similarity and we conclude that a strong source is the periodicity in the users behavior. The tests revealed that there is a strong connection between access rate from hour to hour. We also report the hit rate and weighted hit rate obtained by running a trace driven simulation on the workloads to simulate a proxy with infinite cache, similarly, accesses to unique servers and URLs are a small portion of the total. By considering these characteristics of traffic we can improve the utility of caching for WWW clients
A Study and Project-Based Evaluation of The Software Engineering Evaluation System (SEES)
No full textThe purpose of this document is to describe the design and execution of the quasi-experiment conducted in the Department of Computer Science, Virginia Tech, in accordance with the procedures described in the document "An Experimental Design for Evaluating SEES" prepared for NASA under contract NAS1-19610, Task 17. (Hereafter, that report is called the general design document.) The quasi-experiment serves three important purposes. First, the quasi-experiment is the proof of concept of the general experiment design. It shows that the procedures defined in the general experiment design can be implemented. Second, provides details for setting up a true experiment: identifying the research hypothesis, designing the investigation, selecting various variables, procedures, and controls, measuring the variables, and evaluating the results. Third, any insights revealed during the course of the quasi-experiment can be incorporated in the costly true experiment, thus providing a cost-effective experimental methodology. This report contains sufficient information so that the quasi-experiment can be replicated at an appropriate level of abstraction. We also document and interpret all the results of the quasi-experiment
Stability and Postbuckling of a Platform with Flexible Legs Resting on a Slippery Surface
No full textA rigid platform is supported by thin elastic legs. The legs are able to slide on the ground as they deform. The governing equations for large deformations are formulated and solved numerically by homotopy and quasi-Newton methods. Nonlinear phenomena such as nonuniqueness are found. A global critical load for nonlinear stability is presented
HOMPACK90: A Suite of FORTRAN 90 Codes for Globally Convergent Homotopy Algorithms
No full textHOMPACK90 is a FORTRAN 90 version of the FORTRAN 77 package HOMPACK (Algorithm 652), a collection of codes for finding zeros or fixed points of nonlinear systems using globally convergent probability-one homotopy algorithms. Three qualitatively different algorithms - ordinary differential equation based, normal flow, quasi-Newton augmented Jacobian matrix - are provided for tracking homotopy zero curves, as well as separate routines for dense and sparse Jacobian matrices. A high level driver for the special case of polynomial systems is also provided. Changes to HOMPACK include numerous minor improvements, simpler and more elegant interfaces, use of modules, new end games, support for several sparse matrix data structures, and new iterative algorithms for large sparse Jacobian matrices
Modeling Transcient Trace Data
No full textThis paper introduces a novel technique to construct an empirical workload model fitting time-varying (transient) trace data. The trace can be a categorical or numerical time-series. We model the trace as a Piecewise Independent stochastic process. To estimate the parameters for our model we first build a Rate Evolution Graph from the trace data. Piecewise linear regression is then used to construct a joint time-dependent probablity mass function for the trace data. Two methods are proposed to build a parsi- monious model. The modeling approach is demonstrated by the application of our model to twelve traces from the performance analysis domain
Variable-Complexity Response Surface Approximations for Wing Structural Weight in HSCT Design
No full textA procedure for generating and using a polynomial approximation to wing bending material weight of a High Speed Civil Transport (HSCT) is presented. Response surface methodology is used to fit a quadratic polynomial to data gathered from a series of structural optimizations. Several techniques are employed in order to minimize the number of required structural optimizations and to maintain accuracy. First, another weight function based on statistical data is used to identify a suitable model function for the response surface. In a similar manner, geometric and loading parameters that are likely to appear in the response surface model are also identified. Next, simple analysis techniques are used to find regions of the design space where reasonable HCST designs could occur. The use of intervening variables along with analysis of variance reduce the number of polynomial terms in the response surface model function. Structural optimization is then performed by the program GENESIS on a 28-node Intel Paragon. Finally, optimizations of the HSCT are completed both with and without the response surface