Estimating and eliminating redundant data transfers over the web: a fragment based approach

Redundant data transfers over the Web, can be mainly attributed to the repeated transfers of unchanged data. Web caches and Web proxies are some of the solutions that have been proposed, to deal with the issue of redundant data transfers. In this paper we focus on the efficient estimation and reduction of redundant data transfers over the Web. We first prove that a vast amount of redundant data is transferred in Web pages that are considered to carry fresh data. We show this by following an approach based on Web page fragmentation and manipulation. Web pages are broken down to fragments, based on specific criteria. We then deal with these fragments as independent constructors of the Web page and study their change patterns independently and in the context of the whole Web page. After the fragmentation process, we propose solutions for dealing with redundant data transfers. This paper has been based on our previous work on ‘Web Components’ but also on related work by other researchers. It utilises a proxy based, client/server architecture, and imposes changes to the algorithms executed on the Proxy server and on clients. We show that our proposed solution can considerably reduce the amount of redundant data transferred on the Web. Copyright © 2004 John Wiley & Sons, Ltd.     

Sensitivity of torsional stress predictions of diesel generatorsets to critical parameter values

In the present paper a new method is presented for the evaluation of torsional stressing of diesel-generator sets consisting of components with uncertain torsional characteristics. A frequency scanning technique is implemented for eigenvalue analysis of the elastic system. Due to the uncertainty of the values of stiffness and damping coefficients, a sensitivity analysis method is also presented, suitable for the evaluation of the range of the mechanical stresses. Special consideration is given to the correct simulation of the coupling to the electric network, including the influence of generator regulators and possible network interactions. An exact formula is extracted for the synchronizing and damping torque coefficients. The method presented was checked in a diesel power station of the autonomous electric system of a Greek island     

Investigation of oscillatory problems of hydraulic generating unitsequipped with Francis turbines

In the paper a method is presented for the study of oscillatory problems of hydraulic generating units equipped with Francis turbines. The accurate equations of the turbine are implemented for the simulation, taking into account water hammer effect. Partial derivatives of turbine flow rate and torque with respect to head and gate opening are deduced from real measurements for the whole leading range. Speed governor dynamics are fully simulated, and the influence of torsional vibrations is studied. The vibration response of the unit to draft tube surges is investigated and the risk of excessive oscillations is evaluated. The approach was developed for diagnosis of excessive vibrations of Kastraki hydro power station in Greece     

A comparative study of visual function of young myopic adults wearing contact lenses vs. spectacles

PurposeTo evaluate the impact of contact lenses wear vs. spectacles wear on visual function of young adults with mild to moderate myopia.Methods57 students (27 male and 30 female) with a mean age of 23 years old participated in the study. Their mean best corrected visual acuity was 10/10 binocularly, all suffered from mild to moderate myopia (?3.75 sph/SD 1.25 sph) and they were both contact lenses and spectacles wearers. The VF-14 questionnaire was administered to assess the contact lenses wear vs. spectacles wear impact score on general daily living among the young individuals. It was used translated in Greek after following the ‘translation-back translation’ procedure.ResultsThe mean VF-14 score among spectacles and contact lenses wearers was 100 and 86.78 (SD 4.08) respectively. Although there was a significant difference between the two groups (p < 0.05), both scores were related to a satisfactory functional vision for daily living. The contact lenses wearers were facing difficulty especially while driving at night, seeing steps, as well as doing fine handwork (i.e. sewing, knitting or carpentry).ConclusionsThe use of both spectacles and contact lenses provides satisfactory visual functioning for daily activities in young individuals suffering from mild to moderate myopia. However, there is a spectacles’ wear superiority in personal satisfaction when compared to contact lenses.     

The influence of anisotropic stress on the electrical characteristics of GaAs1-xPx diodes

Anisotropic stress has been applied on shallow light emitting GaAsP junctions with stylii of relatively small radius of curvature made of diamond and—for the purpose of extracting the emitted radiation—of glass. It was found that the induced current changes, which were restricted to the (q/2kT) slope region of the forward bias current voltage characteristic and which is dominated by the Generation Recombination (GR)_current in the junction, were reversible. The currents flowing in the (q/kT) forward bias—light emitting—region and reverse bias region were not affected by stress. No changes in the spectral output in the (q/kT) region could be observed.In sharp contrast the near uniaxial stresses caused by glass stylii with large radii of curvature to which large forces were applied resulted in measurable (reversible) band gap changes as detected by the emitted radiation yet, despite the much higher stresses throughout the diode area, did not affect the currents in the GR domain. Highly anisotropic stress fields, though not necessarily high stresses seem therefore essential in the creation and/or changes of GR centres. An empirical relation of the excess stress induced electric currents with force F derived from experimental data is utilised to extract a theoretical relationship between local concentration of stress induced GR centres and elastic deformation energy. The theory confirms the requirement of an anisotropic stress field for the creation of these excess GR centres in the junction.     

Keyword-guided word spotting in historical printed documents using synthetic data and user feedback

In this paper, we propose a novel technique for word spotting in historical printed documents combining synthetic data and user feedback. Our aim is to search for keywords typed by the user in a large collection of digitized printed historical documents. The proposed method consists of the following stages: (1) creation of synthetic image words; (2) word segmentation using dynamic parameters; (3) efficient feature extraction for each word image and (4) a retrieval procedure that is optimized by user feedback. Experimental results prove the efficiency of the proposed approach.     

Predictive Prefetching on the Web and Its Potential Impact in the Wide Area

The rapid increase of World Wide Web users and the development of services with high bandwidth requirements have caused the substantial increase of response times for users on the Internet. Web latency would be significantly reduced, if browser, proxy or Web server software could make predictions about the pages that a user is most likely to request next, while the user is viewing the current page, and prefetch their content.In this paper we study Predictive Prefetching on a totally new Web system architecture. This is a system that provides two levels of caching before information reaches the clients. This work analyses prefetching on a Wide Area Network with the above mentioned characteristics. We first provide a structured overview of predictive prefetching and show its wide applicability to various computer systems. The WAN that we refer to is the GRNET academic network in Greece. We rely on log files collected at the network's Transparent cache (primary caching point), located at GRNET's edge connection to the Internet. We present the parameters that are most important for prefetching on GRNET's architecture and provide preliminary results of an experimental study, quantifying the benefits of prefetching on the WAN. Our experimental study includes the evaluation of two prediction algorithms: an n most popular document algorithm and a variation of the PPM (Prediction by Partial Matching) prediction algorithm. Our analysis clearly shows that Predictive prefetching can improve Web response times inside the GRNET WAN without substantial increase in network traffic due to prefetching.