Virginia Tech - Wake Forest University School of Biomedical Engineering & Sciences
Computer Science Technical Reports @Virginia TechNot a member yet
997 research outputs found
Sort by
The Effectiveness of Cache Coherence Implemented on the Web
Get PDFThe popularity of the World Wide Web (Web) has generated so much network traffic that it has increased concerns as to how the Internet will scale to meet future demand. The increased population of users and the large size of files being transmitted have resulted in concerns for different types of Internet users. Server administrators want a manageable load on their servers. Network administrators need to eliminate unnecessary traffic, thereby allowing more bandwidth for useful information. End users desire faster document retrieval. Proxy caches decrease the number of messages that enter the network by satisfying requests before they reach the server. However, the use of proxies introduces a concern with how to maintain consistency among cached document versions.
Existing consistency protocols used in the Web are proving to be insufficient to meet the growing needs of the World Wide Web population. For example, too many messages are due to caches guessing when their copy is inconsistent. One option is to apply the cache coherence strategies already in use for many other distributed systems, such as parallel computers. However, these methods are not satisfactory for the World Wide Web due to its larger size and range of users. This paper provides insight into the characteristics of document popularity and how often these popular documents change. The frequency of proxy accesses to documents is also studied to test the feasibility of providing coherence at the server. The main goal is to determine whether server invalidation is the most effective protocol to use on the Web today. We make recommendations based on how frequently documents change and are accessed
Personalizing the GAMS Cross-Index
Get PDFThe NIST Guide to Available Mathematical Software (GAMS)system at http://gams.nist.gov serves as the gateway to thousands of scientific codes and modules for numerical com-putation.We describe the PIPE personalization facility for GAMS,whereby content from the cross-index is specialized for a user desiring software recommendations for a specific problem instance.The key idea is to (i)mine structure,and (ii)exploit it in a programmatic manner to generate personalized web pages.Our approach supports both content based and collaborative personalization and enables information integration from multiple (and complementary)web resources.We present case studies for the domain of linear,second-order,elliptic partial differential equations that indicate strong empirical evidence for the usefulness of our semi-automatic approach
Parallel Global Aircraft Configuration Design Space Exploration
Get PDFThe preliminary design space exploration for large,interdisciplinary engineering problems is often a difficult and time-consuming task. General techniques are needed that efficiently and methodically search the design space. This work focuses on the use of parallel load balancing techniques integrated with a global optimizer to reduce the computational time of the design space exploration. The method is applied to the multidisciplinary design of a High Speed Civil Transport (HSCT). A modified Lipschitzian optimization algorithm generates large sets of design points that are evaluated concurrently using a variety of load balancing schemes.The load balancing schemes implemented in this study are: static load balancing, dynamic load balancing with a master-slave organization, fully distributed dynamic load balancing, an fully distributed dynamic load balancing via threads. All of the parallel computing schemes have high parallel efficiencies. When the variation in the design evaluation times is small, the computational overhead needed for fully distributed dynamic load balancing is substantial enough so that it is more efficient to use a master-slave paradigm. However, when the variation in evaluation times is increased, fully distributed load balancing is the most efficient
VizCraft: A Problem Solving Environment for Configuration Design of High Speed Civil Transport
No full textWe describe a problem solving environment (PSE) named VizCraft that aids aircraft designers during the conceptual design stage. At this stage,an aircraft design is defined by a vector of 10-30 parameters. The goal is to find a vector that minimizes a performance-based objective function while meeting a series of constraints. VizCraft integrates the simulation code that evaluates a design with visualization for analyzing a design individually or in contrast to other designs. VizCraft allows the designer to easily switch between the view of a design in the form of a parameter set, and a visualization of the corresponding aircraft geometry. The user can easily see which, if any, constraints are violated. VizCraft also allows the user to view a database of designs using parallel coordinates. Keywords: Problem solving environment,scientific data visualization, mutlidiimensional visualization, aircraft design, multidisciplinary design optimization
Quantum Computing Applied to Optimization
No full textOptimization problems represent a class of problems that can be time consuming to solve and very complex. In this paper, a quantum algorithm for solving optimization problems is proposed. The algorithm utilizes the encoding scheme from genetic algorithms to encode the problem and then uses Grover's unitary transformation to seek out a solution. The efficiency of the algorithm depends on the length of the chromosome or the coded variable. As a simple example the satisfiability problem, an NP-complete problem, is examined using the algorithm and the time complexity of solving this problem is greatly improved. The traveling salesman and minimum spanning tree problems are also briefly discussed
An Operation Model Supporting the Generation of Requirements That Capture Customer Intent
No full textProduct quality is a direct reflection of how well it meets the cutomer's needs. Hence, the ability to capture customer requirements correctly and succinctly is paramount. Unfortunately, within software development frameworks the gathering of requirements is one of the more ill-defined and least structured processes. To address this inadequacy, our paper (a) proposes a refinement (or decomposition) to the requirements generation phase that admits to detailed examination and promotes a better understanding of where requirements generation goes wrong,(b) using the results of a preliminary study, identifies where and how miscommunication and requirements omission occur, and (c) outlines a more structured process that can be applied early in the requirements generation process to minimize requirement faults
System Resource Sharing for Synchronous Collaboration
Get PDFWe describe problems associated with accessing data resources external to the application, which we
term externalities, in replicated synchronous collaborative applications (e.g., a multiuser text editor).
Accessing externalities such as les, databases, network connections, environment variables and the
system clock is not as straightforward in replicated collaborative software as in single-user applications
and centralized collaborative systems. We describe ad hoc solutions that have been used previously. Our
primary objection to the ad hoc solutions is that the developer must program dierent behavior into the
dierent replicas of a multi-user application, which increases the cost and complexity of development.
We introduce a novel general approach to accessing externalities uniformly in a replicated collaborative
system. The approach uses a semi-replicated architecture where the actual externality resides at a single
location and is accessed via replicated proxies. The proxies multiplex input to and output from the single
instance of the externality. This approach facilitates the creation of replicated synchronous groupware
in two ways: (1) developers use the same mechanisms as in traditional single-user applications (2)
developers program all replicas to execute the same behavior. We describe a general design for proxied
access to read{only, write{only and read{write externalities. We discuss the tradeos of this semi-
replicated approach over full, literal replication and the class of applications to which this approach can
be successfully applied. We also describe details of a prototype implementation of this approach within
a replicated collaboration-transparency system, called Flexible JAMM (Java Applets Made Multi-user)
Theory of Globally Convergent Probability-One Homotopies For Nonlinear Programming
No full textFor many years, globally convergent probability-one homotopy methods have been remarkably successful on difficult realistic engineering optimization problems, most of which were attacked by homotopy methods because other optimization algorithms failed or were ineffective. Convergence theory has been derived for a few particular problems, and considerable fixed point theory exists, but generally convergence theory for the homotopy maps used in practice for nonlinear constrained optimization has been lacking. This paper derives some probability-one homotopy convergence theorems for unconstrained and constrained optimization, for linear and nonlinear constraints, and with and without convexity. Some insight is provided into why the homotopies used in engineering practice are so successful, and why this success is more than dumb luck. By presenting the theory as variations on a prototype probability-one homotopy convergence theorem, the essence of such convergence theory is elucidated
HSCT Configuration Design Space Exploration Using Aerodynamic Response Surface Approximations
No full textA method has been developed to generate and use polynomial approximations to the range and cruise drag components in a highly constrained, multidisciplinary design optimization of a High Speed Civil Transport configuration. The method improves optimization performance by eliminating the numerical noise present in the analyses through the use of response surface methodology. In our implementation, we fit quadratic polynomials within variable bounds to data gathered from a series of numerical analyses of different aircraft designs. Because the HSCT optimization process contains noise and suffers from a nonconvex design space even when noise is filtered out, multiple optimization runs are performed from different starting points with and without the response surface models in order to evaluate their effectiveness. It is shown that response surface methodology facilitates design space exploration, allowing improvements in terms of both convergence performance and computational effort when multiple starting points are required
Verification and Validation: What Impact Should Project Size and Complexity Have on Attendant V&V Activities and Supporting Infrastructure?
No full textThe size and complexity of Modeling and Simulation (M&S) application continue to grow at a significant rate. The focus of this panel is to examine the impact that such growth should have on attendant Verification and Validation (V&V) activities. Two prominent considerations guiding the panel discussion are: (1) Extending the current M&S development objectives to include quality characteristics like maintainability, reliability, and reusability -- the current modus operandi focuses primarily on correctness, and (2) Recognizing the necessity and benefits of tailoring V&V activities commensurate with the size of the project, i.e., one size does not fit all. In this paper we provide six questions and four sets of responses to those questions. These questions and responses are intended to foster additional thought and discussion on topics crucial to the synthesis of quality M&S applications