Prefetching in Content Distribution Networks via Web Communities Identification and Outsourcing

Content distribution networks (CDNs) improve scalability and reliability, by replicating content to the “edge” of the Internet. Apart from the pure networking issues of the CDNs relevant to the establishment of the infrastructure, some very crucial data management issues must be resolved to exploit the full potential of CDNs to reduce the “last mile” latencies. A very important issue is the selection of the content to be prefetched to the CDN servers. All the approaches developed so far, assume the existence of adequate content popularity statistics to drive the prefetch decisions. Such information though, is not always available, or it is extremely volatile, turning such methods problematic. To address this issue, we develop self-adaptive techniques to select the outsourced content in a CDN infrastructure, which requires no apriori knowledge of request statistics. We identify clusters of “correlated” Web pages in a site, called Web site communities, and make these communities the basic outsourcing unit. Through a detailed simulation environment, using both real and synthetic data, we show that the proposed techniques are very robust and effective in reducing the user-perceived latency, performing very close to an unfeasible, off-line policy, which has full knowledge of the content popularity.     

Performance Evaluation of the Impact of QoS Mechanisms in an IPv6 Network for IPv6-Capable Real-Time Applications

This paper describes a Quality of Service (QoS) service on an IPv6 domain that aims to service aggregates of real-time traffic with minimum delay, jitter, and packet loss. It contains results from the tests that were performed in order to configure and evaluate the QoS mechanisms. As an actual example of real-time traffic, we have used the OpenH323 project, an open source H.323 implementation that has been ported to IPv6. The QoS mechanisms in IPv6 networks is still a field that has not been researched adequately, and we therefore present the results from the experiments in our IPv6 network that took advantage of the QoS mechanisms. This QoS service uses the Modular QoS CLI (MQC) mechanism and especially the Low Latency Queue feature (LLQ) in order to treat packets from real-time applications.     

New methods for digital modeling of historic sites

We discuss new methods for building 3D models of historic sites. Our algorithm automatically computes pairwise registrations between individual scans, builds a topological graph, and places the scans in the same frame of reference.     

A symmetric fragment and replicate algorithm for distributed joins

It is shown that the fragment and replicate (FR) distributed join algorithm is a special case of the symmetric fragment and replicate (SFR) algorithm, which improves the FR algorithm by reducing its communication. The SFR algorithm, like the FR algorithm, is applicable to N-way joins and nonequijoins and does tuple balancing automatically. The authors derive formulae that show how to minimize the communication in the SFR algorithm, discuss its performance on a parallel database prototype, and evaluate its practicality under various conditions. It is claimed that SFR improves the worst-case cost for a distributed join, but it will not displace specialized distributed join algorithms when the later are applicable     

The role of barium enema in colostomy closure in trauma patients

Recently, the routine use of barium enema preceding colostomy closure in trauma patients has been challenged. It has been argued that the nature of the injury should be apparent from the initial laparotomy and that the likelihood of finding an unsuspected colonic lesion in the young, previously healthy patients who constitute the majority of trauma patients is very small. We retrospectively reviewed 124 consecutive cases of patients who received colostomy takedowns for trauma. One hundred six of the patients had preoperative barium enema evaluation. 87.1 per cent of the examinations were negative, with a subsequent stoma closure complication rate of 20.4 per cent. Of the 13 positive barium enemas, 9 were falsely positive. These patients had a higher stoma closure complication rate of 39 per cent, a fact that could not be explained on the basis of their abnormal studies. The 18 patients who did not have barium enema performed did not have an increase in complications (17.6%). Barium enema failed to uncover unsuspected pertinent diagnoses, often added unnecessary delays and expense, and in no case changed the operative management. Contrast studies were found to be useful in defining anatomy in cases of known fistulas and when the takedowns were performed without the benefit of operative reports from the previous surgery.     

SPRINT II: a second generation single photon ring tomograph

SPRINT II is a stationary detector ring tomograph designed for brain imaging. Eleven two-dimensional sodium iodide camera modules that use maximum-likelihood position logic are arranged in a 50-cm-diameter ring with a scintillator packing fraction of 96%. A 34-cm-diameter rotating lead aperture ring containing either 10 or 12 slits is used for in-plane collimation, while the z-axis collimator is constructed of parallel lead foil rings. The field of view is 22 cm in diameter by 12 cm long. Sensitivity is 10 count/s/muCi for an on-axis (99m)Tc point source and 8500 count/s/muCi/cm(3) for 19.8-cm-diameter by 6.2-cm-long cylindrical source. Longitudinal resolution is 10 mm FWHM, and in-plane resolution varies from 8 mm FWHM on-axis to 5 mm FWHM at a radius of 9 cm. Performance results are presented.     

Biodiesel production using tetramethyl- and benzyltrimethyl ammonium hydroxides as strong base catalysts

In recent years, the acceptance of fatty acid methyl esters (biodiesel) as an alternative fuel has rapidly grown in EU. The most common method for biodiesel production is based on triglyceride transesterification to methyl esters with dissolved sodium hydroxide in methanol as catalyst. In this study, cottonseed oil and used frying oil were subjected to the transesterification reaction with tetramethyl ammonium hydroxide and benzyltrimethyl ammonium hydroxide as strong base catalysts. This work investigates the optimum conditions for biodiesel production using amine-based liquid catalysts. Biodiesel ester content was strongly related with the type of feedstock and the reaction variables, such as those of the catalyst concentration, methanol to oil molar ratio, and reaction time. The overall results suggested that the transesterification of cottonseed oil achieved high conversion rates with both catalysts, while the use of waste oil resulted in lower yields of methyl esters due to the possible formation of amides.     

Joining silicon nitride to itself and to metals

This article reviews the progress that has been made in developing and applying joining techniques for Si₃N₄ and discusses our understanding of the influence of process selection on the materials science of the formation and properties of joints. High-performance Si₃N₄ joints can be produced, but it is clear that much work remains to be done before the use of such joints in hot-stressed applications can be disregarded as a problem.