Analyzing web server performance under dynamic user workloads

The increasing popularity of web applications has introduced a new paradigm where users are no longer passive web consumers but they become active contributors to the web, specially in the contexts of social networking, blogs, wikis or e-commerce. In this new paradigm, contents and services are even more dynamic, which consequently increases the level of dynamism in user's behavior. Moreover, this trend is expected to rise in the incoming web. This dynamism is a major adversity to define and model representative web workload, in fact, this characteristic is not fully represented in the most of the current web workload generators. This work proves that the web user's dynamic behavior is a crucial point that must be addressed in web performance studies in order to accurately estimate system performance indexes. In this paper, we analyze the effect of using a more realistic dynamic workload on the web performance metrics. To this end, we evaluate a typical e-commerce scenario and compare the results obtained using different levels of dynamic workload instead of traditional workloads. Experimental results show that, when a more dynamic and interactive workload is taken into account, performance indexes can widely differ and noticeably affect the stress borderline on the server. For instance, the processor usage can increase 30% due to dynamism, affecting negatively average response time perceived by users, which can also turn in unwanted effects in marketing and fidelity policies. © 2012 Elsevier B.V. All rights reserved.This work has been partially supported by the Spanish Ministry of Science and Innovation under Grant TIN-2009-08201.Peña Ortiz, R.; Gil Salinas, JA.; Sahuquillo Borrás, J.; Pont Sanjuan, A. (2013). Analyzing web server performance under dynamic user workloads. Computer Communications. 36(4):386-395. https://doi.org/10.1016/j.comcom.2012.11.005S38639536

Verification of a new CFD compressible segregated and multi-phase solver with different flux updates-equations sequences

A new solver capable of calculating liquid and/or gas problems has been developed, verified and validated. Compressible solvers in Computational Fluid Dynamics use both mass flux and volumetric fluxes through the cell surface to calculate derivative terms. These fluxes depend on density and velocity fields, therefore the stability of the solver is affected by "how" and "where" density and velocity are calculated or updated. In addition to verification and validation, this paper deals with how different flux updates-equations sequences change the computational solution, reaching the conclusion that for mono-phase solvers no extra-updates should be used in order to minimize computational cost, but for multi-phase solvers with high density gradients an extra-update should be implemented to improve the stability of the solver.This research was funded in the frame the project "Comprension de la influencia de combustibles no convencionales en el proceso de inyeccion y combustion tipo Diesel" reference TRA2013-36932 from Ministerio de Enonomia y Competitividad (Spanish Ministry of Economy).Payri, R.; Ruiz Rosales, S.; Gimeno, J.; Marti-Aldaravi, P. (2015). Verification of a new CFD compressible segregated and multi-phase solver with different flux updates-equations sequences. Applied Mathematical Modelling. 39(2):851-861. https://doi.org/10.1016/j.apm.2014.07.011S85186139

Enhancing process control education using a web-based interactive multimedia environment

10.1016/S1570-7946(03)80519-9Computer Aided Chemical Engineering15C1478-148

Response spectrum of non-linear spring mass system subjected to transient disturbances

The transient response spectrum of a cubic spring mass system subjected to a step function input is obtained. An approximate method is adopted where non-linear restoring force characteristic is replaced by two linear segments, so that the mean square error between them is a minimum. The effect of viscous damping on the peak response is also discussed for various values of the damping constant and the non-linearity restoring force parameter

Optimal supply chain redesign using genetic algorithm

10.1016/S1570-7946(07)80140-4Computer Aided Chemical Engineering24703-70

Thermal diffusivity of IV-V-VI glassess - an evidence for the existence of a mechanical threshold

The thermal diffusivity of two sets of GexSbySe100-x-y, GexAsyTe100-x-y and SixAsyTe100-x-y glasses have been measured using the photoacoustic technique. The thermal diffusivity data of the three glass systems show maxima at the compositions corresponding to the average coordination number <r> = 2.60. These results have been interpreted in the light of the existence of a mechanical threshold and the formation and development of a layered structure in these network glasses

Interaction of carbon monoxide with transition metal surfaces

XPS studies of the interaction of carbon monoxide with surfaces of Fe, Co and Ni indicate that at 300 K, the disproportionation reaction is prominent up to exposures of 103 L giving rise to high surface concentrations of carbon. At higher exposures and higher temperatures, dissociation of carbon monoxide accompanied by the formation of surface oxide layers becomes more prominent. In the case of copper, disproportionation is prominent up to 104 L even at 500 K followed by dissociation at higher exposures. These results are also supported by Auger spectroscopic studies