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Distribution by Scientific Domains
Engineering60%

Selected Abstracts

Class-based weighted fair queueing: validation and comparison by trace-driven simulation

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 10 2005
Rachid El Abdouni Khayari
Abstract World-wide web as well as proxy servers rely for their scheduling on services provided by the underlying operating system. In practice, this means that some form of first-come-first-served (FCFS) scheduling is utilized. Although FCFS is a reasonable scheduling strategy for job sequences that do not show much variance, for the world-wide web it has been shown that the requested-object sizes do exhibit heavy tails. Under these circumstances, job scheduling on the basis of shortest-job first (SJF) or shortest remaining processing time (SRPT) has been shown to minimize the total average waiting time. However, these methods have the disadvantage of potential job starvation. In order to avoid the problems of both FCFS and SJF we present in this paper a new scheduling approach called class-based interleaving weighted fair queueing (CI-WFQ). This scheduling approach exploits the specific characteristics of the job stream being served, that is, the distribution of the sizes of the objects being requested, to set its parameters such that good mean response times are obtained and starvation does not occur. In that sense, the new scheduling strategy can be made adaptive to the characteristics of the job stream being served. In this paper we compare the new scheduling approach (using trace-driven simulations) to FCFS, SJF and the recently introduced ,-scheduling, and show that CI-WFQ combines very good performance (as far as mean and variance of response time and blocking probability are concerned) with a scheduling complexity almost as low as for FCFS (and hence, lower than for SJF and ,-scheduling). The use of trace-driven simulation is essential, since the special properties of the arrival process makes analytical solutions very difficult to achieve. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Future integrated learning environments with multimedia

JOURNAL OF COMPUTER ASSISTED LEARNING, Issue 1 2001
T. Okamoto
Abstract, Recent progress in information technology hardware and the spread of the Internet have opened a variety of new ways for many fields. Although slower than the business field to catch up with these new developments, the educational field has gradually migrated towards the World-wide web, mostly under the slogan of free, accessible education, to and from anyplace, at anytime. This development triggered an important shift from the teaching paradigm to the learning paradigm. However, slow network speed hindered the first learning environments from being more than simple, electronic text-books. The latest trends making use of increased bandwidths and integrating various media to enhance learning. Moreover, for obtaining learner-oriented, customised learning environ-ments, intelligent tutoring techniques are being adapted and developed for the web. This paper presents these trends on one hand, but on the other hand, also addresses the dangers and pitfalls that such an avalanche of change can bring and stresses the task of ensuring that the real goal of enhancing and improving learning is not overlooked. [source]

Development of a web-based integrated manufacturing laboratory

COMPUTER APPLICATIONS IN ENGINEERING EDUCATION, Issue 4 2001
Samuel H. Huang
Abstract The internet is dramatically changing the ways we learn and teach, as well as the way we interact as a society. The "same time, same place, only some people" traditional instructional method is giving way to "anytime, anyplace, anybody" educational models. This paper deals with the development of a Web-based integrated manufacturing laboratory (WIML), which represents a virtual mini-manufacturing corporation, whose aim is to support core manufacturing curriculum and to provide students with hands-on experience on various manufacturing functions and effective use of manufacturing software tools. Key components of the WIML include a manufacturing tutor, a data repository, message boards, customization pages, and links to the world-wide web. The WIML not only can stimulate students' interest in related manufacturing courses but also allow them to strengthen their computer skills and develop ability to work as a team. © 2002 Wiley Periodicals, Inc. Comput Appl Eng Educ 9: 228,237, 2001; Published online in Wiley InterScience (www.interscience.wiley.com.); DOI 10.1002/cae.10006 [source]

Class-based weighted fair queueing: validation and comparison by trace-driven simulation

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 10 2005
Rachid El Abdouni Khayari
Abstract World-wide web as well as proxy servers rely for their scheduling on services provided by the underlying operating system. In practice, this means that some form of first-come-first-served (FCFS) scheduling is utilized. Although FCFS is a reasonable scheduling strategy for job sequences that do not show much variance, for the world-wide web it has been shown that the requested-object sizes do exhibit heavy tails. Under these circumstances, job scheduling on the basis of shortest-job first (SJF) or shortest remaining processing time (SRPT) has been shown to minimize the total average waiting time. However, these methods have the disadvantage of potential job starvation. In order to avoid the problems of both FCFS and SJF we present in this paper a new scheduling approach called class-based interleaving weighted fair queueing (CI-WFQ). This scheduling approach exploits the specific characteristics of the job stream being served, that is, the distribution of the sizes of the objects being requested, to set its parameters such that good mean response times are obtained and starvation does not occur. In that sense, the new scheduling strategy can be made adaptive to the characteristics of the job stream being served. In this paper we compare the new scheduling approach (using trace-driven simulations) to FCFS, SJF and the recently introduced ,-scheduling, and show that CI-WFQ combines very good performance (as far as mean and variance of response time and blocking probability are concerned) with a scheduling complexity almost as low as for FCFS (and hence, lower than for SJF and ,-scheduling). The use of trace-driven simulation is essential, since the special properties of the arrival process makes analytical solutions very difficult to achieve. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Conservation strategy maps: a tool to facilitate biodiversity action planning illustrated using the heath fritillary butterfly

JOURNAL OF APPLIED ECOLOGY, Issue 2 2003
G. J. Holloway
Summary 1.,The UK Biodiversity Action Plan (UKBAP) identifies invertebrate species in danger of national extinction. For many of these species, targets for recovery specify the number of populations that should exist by a specific future date but offer no procedure to plan strategically to achieve the target for any species. 2.,Here we describe techniques based upon geographic information systems (GIS) that produce conservation strategy maps (CSM) to assist with achieving recovery targets based on all available and relevant information. 3.,The heath fritillary Mellicta athalia is a UKBAP species used here to illustrate the use of CSM. A phase 1 habitat survey was used to identify habitat polygons across the county of Kent, UK. These were systematically filtered using relevant habitat, botanical and autecological data to identify seven types of polygon, including those with extant colonies or in the vicinity of extant colonies, areas managed for conservation but without colonies, and polygons that had the appropriate habitat structure and may therefore be suitable for reintroduction. 4.,Five clusters of polygons of interest were found across the study area. The CSM of two of them are illustrated here: the Blean Wood complex, which contains the existing colonies of heath fritillary in Kent, and the Orlestone Forest complex, which offers opportunities for reintroduction. 5.,Synthesis and applications. Although the CSM concept is illustrated here for the UK, we suggest that CSM could be part of species conservation programmes throughout the world. CSM are dynamic and should be stored in electronic format, preferably on the world-wide web, so that they can be easily viewed and updated. CSM can be used to illustrate opportunities and to develop strategies with scientists and non-scientists, enabling the engagement of all communities in a conservation programme. CSM for different years can be presented to illustrate the progress of a plan or to provide continuous feedback on how a field scenario develops. [source]