42642346
Multi-version memory: software cache management for concurrent B-trees
The authors describe a new concurrent B-tree algorithm. The algorithm is designed to work well in large-scale parallel or distributed systems in which the number of processors sharing the tree is large or the communication delay between processors (or between processors and the global memory for a shared-memory system) is large relative to the speed of local computation. The basis of the algorithm is an abstraction that is similar to coherent shared memory, but provides a weaker semantics; this abstraction is called multiversion memory. Multi-version memory uses caches but weakens the semantics of ordinary shared memory by allowing process reading data to be given an old version of the data. This semantics is adequate for the non-leaf nodes in the B-tree algorithms presented.<<ETX>>
10974617
PRELUDE: A System for Portable Parallel Software
Abstract : In this paper we describe PRELUDE, a programming language and accompanying system support for writing portable MIMD parallel programs. PRELUDE supports methodology for designing and organizing parallel programs that makes them easier to tune for particular architectures and to port to new architectures. It builds on earlier work on Emerald, Amber, and various Fortran extensions to allow the programmer to divide programs into architecture-dependent and architecture-independent parts, and then to change the architecture-dependent parts to port the program to a new machine or to tune its performance on a single machine. The architecture-dependent parts of a program are specified by annotations that describe the mapping of a program onto a machine. PRELUDE provides a variety of mapping mechanisms similar to those in other systems, including remote procedure call, object migration, and data replication and partitioning. In addition, PRELUDE includes novel migration mechanisms for computations based on a form of continuation passing. The implementation of object migration in PRELUDE uses a novel approach based on fixup blocks that is more efficient than previous approaches, and amortizes the cost of each migration so that the cost per migration drops as the frequency of migrations increases.
14708626
Computation migration: enhancing locality for distributed-memory parallel systems
We describe computation migration, a new technique that is based on compile-time program transformations, for accesing remote data in a distributed-memory parallel system. In contrast with RPC-style access, where the access is performed remotely, and with data migration, where the data is moved so that it is local, computation migration moves part of the current thread to the processor where the data resides. The access is performed at the remote processor, and the migrated thread portion continues to run on that same processor; this makes subsequent accesses in the thread portion local.
We describe an implementation of computation migration that consists of two parts: an implementation that migrates single activation frames, and a high-level language annotation that allows a programmer to express when migration is desired. We performed experiments using two applications; these experiments demonstrate that computation migration is a valuable alternative to RPC and data migration.
5536996
DMAS: a web-based distributed mathematics assessment system (abstract only)
Assessing student performance and understanding is very important in education generally and in Mathematics education in particular. DMAS is a Web-based Distributed Mathematics Assessment system that can be of great value to teachers and students of Mathematics. Features of DMAS include: DMAD (the core Distributed Mathematics Assessment database), test authoring tool for teachers, online taking of tests, grading and results administration, comprehension diagnoses and linking to remedial materials. DMAS supports many problem types and allows mathematical formulas/expressions as well as geometry drawings/graphs to be part of questions and answers. Furthermore, DMAS supports the use of test taking as a teaching method. A teacher can monitor all students from the teacher terminal in real-time and either verbally guide the whole class on certain points or interact privately with one or more students via the Teacher-Student Interaction Mechanism (TSIM), an instant text-messaging provided by DMAS. A new Assessment Markup Language, MAML, is designed to make tests and test questions easy to share widely on the Web. Although developed as a sub-system of WME (Web-based Mathematics Education), DMAS is an independent Web system easily interfaced to any Web page through a well-defined API. The DMAS system consists of local databases at individual school websites. Teachers may publish new or improved questions to their local DMAS database to be shared with other teachers in the same school and in different schools. Teachers can use the powerful search engine (DMASEngine) to search for assessment questions. Search can be narrowed by subject, topic, grade-level, question type, keyword, and author. DMAD is designed to work as one distributed database while providing power, unity, and convenience at each participating school. The system helps create, revise, administer, and grade exams that can contain various types of questions: multiple choices, true-or-false, extended (essay) questions, short answers, two-columns matching, and fill-the-blank. Questions use a well-designed representation (encoding) allowing correct answers, rubrics, formulas, images, geometrical objects (SVG), and multimedia as well as interactive contents. DMAS system provides different views (modes): teacher and student modes. It also supports two types of testing: online and paper testing. The teacher can set Assessment test display options: display questions by a given order, by random questions none-random options, or by all questions/options are in random order. Tests taken online can be graded automatically and stored for teacher review, analysis, and printing. DMAS Assessment system has been piloted into seventh grade students at Kimpton Middle School, Stow, Ohio on 10/05/2007 for real-life testing and apparently teacher and student's feedback gave good impression and encouraging feedback about the DMAS system. However, our goal is to put DMAS system under extensive trial in schools and collecting feedback and suggestions from teachers, students, school administrators and education experts to help evolve DMAS. As more schools adopt DMAS, the distributed nature of DMAS will be demonstrated in realistic situations. Because DMAS has been designed in consultation with middle school teachers and education experts, the underline DMAS system design and framework is easy and flexible for future changes, requirements, expansions, and customizations. DMAS provides features to support real-life test giving such as loss of power to a laptop and retaking of tests.
5684281
Hopf bifurcation and oscillations in a communication network with heterogeneous delays
In this paper, we investigate stability, bifurcation and oscillations arising in a single-link communication network model with a large number of heterogeneous users adopting a Transmission Control Protocol (TCP)-like rate control scheme with an Active Queue Management (AQM) router. In the system considered, different user delays are known and fixed but taken from a given distribution. It is shown that for any given distribution of delays, there exists a critical amount of feedback (due to AQM) at which the equilibrium loses stability and a limit cycling solution develops via a Hopf bifurcation. The nature (criticality) of the bifurcation is investigated with the aid of Lyapunov-Schmidt perturbation method. The results of the analysis are numerically verified and provide valuable insights into dynamics of the AQM control system.
167446339
Understanding online archiving
38040297
A Mammography Database and View System for the African American Patients
In this research, we have obtained and scanned mammography films (within the last ten years) of African American women treated at Howard University Hospital Radiology Department, constructed a database using the digitized mammography images, and developed an image viewing system to display these digital mammograms. The images are scanned with the high resolution Kodak LS85 laser scanner. The digital mammography database is powered by MySQL and PHP. It also has a Web-based search engine (with secure access) so that the information can be made accessible to all medical team members. The image viewing software, D-Viewer, is coded in C# and is intended to help medical professionals view and retrieve large data sets in near real time. We have already digitized 260 cases (one case per patient, twenty to forty films per case). We also have developed a MySQL-based image database, and a PHP-based web-search engine to retrieve cases that have masses (benign or malignant) or calcifications (benign or malignant). This database has been evaluated by medical professionals and the experimental results obtained so far are very promising (high image qualities, fast access time). We are currently developing an image content-based retrieval function for the database system in order to provide improved search capability for the medical professionals.
6861036
Practical factorization of univariate polynomials over finite fields
Research presented fort to establish state-of-the-art Kent State University “ Kent, Ohio 44242-0001 here is part of an effactoring routines for polynomials. The foundation of such algorithms lies in the efficient factorization over a finite field GF(p~). The Cantor-Zassenhaus algorithm together with innovative ideas suggested by others is compared with the Berlekamp algorithm. The studies led us to design a hybrid algorithm that combine the strengths of the different approaches. The algorithms are also implemented and machine timings are obtained to measure the performance of these algorithms.