Tekhné

14

Authors: Franklin Planchart

The process of packetized networks has facilitated the process of integration of services. To this extent, the characteristics of traffic have had a major twist to a chaotic behavior. This chaos is reflected in repetition of burst of information at all scales of time, which fits in the theory of fractals and self similarities in networks. Protocols such as IP require activation mechanisms that alert to the user , using TCP or SCTP protocol for example, that activate the mechanisms of recovery and decrease of the burst. The phenomena of global synchronization, that brings as a consequence the stagnation of all users by network congestion, are closely related to this selfsimilarities of the traffic, given that transport protocols are isolated from the network. It is therefore necessary to determine the status of the network. Characterize and identify it. This identification is based on the determination of the Hurst parameters, for which there are several methods. The work of three scientists who developed modules in Matlab were analyzed in this development. They are Reinaldo Scappini, Darryl Veitch y Hae-Duck Joshua Jeong. These modules calculate the H parameter with different mathematical methods in the domain of time and frequency, similar to stochastically self similar traffic generated in the same way. The software developed in this work is based on graphical interface. It takes these modules and binds together them in a single application, through a rigorous analysis of integration of the databases, graphics and adaptation of many modules to facilitate automation. A component of the software is geared to the education sector of telecommunications engineering or computing in the last period and another part is oriented to research field of scientist and engineers from the network.

16

Authors: Iván Carmona, Carla Vilchez

Twisted pair has represented, along many years, one of the most used transmission media by telecommunications service providers, all over the world. However, it performance along the frequency spectrum is seriously affected by the attenuation that signals undergo across it, within an average distance between 3.3 and 5Km. Under the hypothetical scenario of a decrease in the propagation length over telephone twisted pairs, the levels of attenuation in signals of higher frequencies than those used by the current telephony and Internet services, would diminish to the point that signals would reach the receiver with an acceptable power and would be recoverable. This would permit the usage of a broader bandwidth on telephone cables than the one used nowadays. The approach has been made in spite of a generalized skepticism in the world about the use of telephone pairs for frequencies over the 2.1MHz (upper limit of ADSL2+). In order to determine the feasibility and conditions under which it would be possible a bandwidth usage optimization, a documental research was made, forming a basis to obtain a characterization of the copper pairs’ behavior, along the frequency spectrum, for a shorter distance than the average. This characterization was obtained through a computer simulation of the line’s behavior, and the subsequent verification of the results through electric measurements on the cables, validating and giving reliability to the mathematic model developed. The results obtained verified the proposed hypothesis, and allowed (in a second part of the research work) the design of a technological proposal to efficiently take advantage of the bandwidth among 2,208KHz and 20,000KHz. “AMODT” (assigned name to the proposal), finally raises the division of the “usable spectrum” in five sub-bands, with the same width and separation used by the ADSL2+ technology, moved in frequency looking for an increase in the spectral efficiency.

18

Authors: Frank Herrera, Aron Pollner

The purpose of this work is to find geometrical and mechanical patterns in the behavior of steel-frame buildings subjected to the loss of part of their support. As geometrical pattern, vertical displacement is used. As mechanical patterns axial, shear and moment diagrams of the structural members are used. These patterns are obtained with the help from computer programs: ETABS (software for the analysis, design and drafting of buildings) and Microsoft Excel. As there are few precedents to this investigation, the authors decided to take into account only the aspects considered by them as the most pertinent to begin with; leaving the door open for future students to get further into other more specific aspects. This is a novel work not only because there is little accessible bibliographic material, but also because it implied the development of an original methodology that relied mostly on visual or graphical tools as principal resources. For the development of this work, only buildings of 5, 10 and 15 floors where used – all of them with the same floor plan configuration. In the same manner, only the central column, the central-of-the-façade column and corner column where chosen. The objective is to find, how the location of the column subjected to the loss of support and the height of the building, influence the patterns mentioned previously. As a result it was found that the order of damage by loss of support, starting from the worst, is: First the central column, then the façade column and lastly the corner column. From this it was observed that, the more weight carried by a column, the more dangerous the loss of support. On the other hand it is also evident that, as the building grows in height, the effect of the loss of support gets stronger.

21

Authors: Oswaldo Suárez, Lucila Vilera

This article is a summary of the Special Degree presented to the UCAB in March 2012 as a requirement for the degree of STRUCTURAL ENGINEERING SPECIALIST. It is the analysis and structural design of a metal bridge, which is simply supported on the piles of the Hydroelectric Dam Spillway “Manuel Piar” (Tocoma). The analysis is based on determining the stress on the beams and diaphragms which constitute the bridge, for which it was subjected to the loads of HS-20-44 trucks and the passage of a crane for service work and maintenance of the maneuver of the gates. The study is the determination of the stress of the influence of the combination of three load cases (step of an HS-20-44, step of two HS-20-44 and finally the step of service Crane in conjunction with an HS-20-44) to which the bridge will be subjected during its lifetime, for which we performed a mathematical model in AutoCad, simulating the members of the bridge as solid elements. This model is used to realize the simulation in ANSYS Workbench software v 12.1, obtaining as results of the simulation the stress due to bending, shear and allowable deflections acting on the bridge structure. These results should be compared with the stress and allowable deflections to determine if the bridge is able to resist the imposed loads or not. Once made such comparison you will be able to see to what percentage of combined stress is working each of the members of the bridge, as of the assembly in general. This is under the different load stages, with which we can deduce the safety factors and the percentage of efficiency of the steel sections which conform the structure of the bridge.