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Sanchez L.V.,University Militar Nueva Granada | Ramirez J.D.,University Militar Nueva Granada | Ramirez J.D.,University of Los Andes, Colombia
Parasitology | Year: 2013

Chagas disease or American trypanosomiasis is a pathology affecting about 8-11 million people in Mexico, Central America, and South America, more than 300Â 000 persons in the United States as well as an indeterminate number of people in other non-endemic countries such as USA, Spain, Canada and Switzerland. The aetiological agent is Trypanosoma cruzi, a protozoan transmitted by multiple routes; among them, congenital route emerges as one of the most important mechanisms of spreading Chagas disease worldwide even in non-endemic countries and the oral route as the responsible of multiple outbreaks of acute Chagas disease in regions where the vectorial route has been interrupted. The aim of this review is to illustrate the recent research and advances in host-pathogen interaction making a model of how the virulence factors of the parasite would interact with the physiology and immune system components of the placental barrier and gastrointestinal tract in order to establish a response against T. cruzi infection. This review also presents the epidemiological, clinical and diagnostic features of congenital and oral Chagas disease in order to update the reader about the emerging scenarios of Chagas disease transmission. © Cambridge University Press 2012.


Carrillo J.,University Militar Nueva Granada | Alcocer S.M.,National Autonomous University of Mexico
Engineering Structures | Year: 2013

As it is widely recognized, seismic design parameters used in most current codes are mainly intended for designing concrete walls in medium- or high-rise buildings. In low-rise concrete housing, thin walls with low concrete strength, web steel ratio smaller than the minimum ratio prescribed by codes, and in many cases, shear web reinforcement made of welded wire meshes are commonly used. In this paper, a simplified equation for estimating the period of vibration of low-rise concrete housing is proposed. The equation is based on response measured during shaking table tests of solid walls and walls with openings, on the results derived from conventional spectral analysis of ambient vibration tests, as well as on results obtained from mathematical models using the wide-column analogy and the finite element method. Statistical analysis of the ratios of predicted-to-measured periods demonstrated that predicted periods were very similar to those observed, and the scatter is also lower than in existing equations. The proposed equation is useful for seismic design, as well as for assessing the adequacy of available equations in current codes. © 2013 Elsevier Ltd.


Carrillo J.,University Militar Nueva Granada | Alcocer S.M.,National Autonomous University of Mexico
Earthquake Engineering and Structural Dynamics | Year: 2013

Experimental evidence supporting the fact that results from quasi-static (QS) test of low-rise reinforced concrete walls may be safely assumed as a lower limit of strength and displacement, and energy dissipation capacities are still scarce. The aim of this paper is to compare the seismic performance of 12 reinforced concrete walls for low-rise housing: six prototype walls tested under QS-cyclic loading and six models tested under shaking table excitations. Variables studied were wall geometry, type of concrete, web steel ratio, type of web reinforcement and testing method. Comparison of results from dynamic and QS-cyclic tests indicated that stiffness and strength properties were dependent on the loading rate, the strength mechanisms associated with the failure mode, the low-cycle fatigue, and the cumulative parameters, such as displacement demand and energy dissipated. Copyright © 2012 John Wiley & Sons, Ltd.


Carrillo J.,University Militar Nueva Granada | Carrillo J.,National Autonomous University of Mexico | Alcocer S.M.,National Autonomous University of Mexico
Engineering Structures | Year: 2012

Aimed at better understanding the seismic behavior of reinforced concrete (RC) walls, typically used in one-to-two stories housing in several Latin American countries, a large investigation project has been carried out. Previous experimental programs considered the behavior of walls subjected to monotonically and cyclically increased loads. This paper compares and discusses displacement and shear strength capacities, as well as the dynamic characteristics of six RC walls tested under shaking table excitations. Variables studied were the wall geometry (solid walls and walls with openings), type of concrete (normalweight and lightweight), web steel reinforcement ratio (0.125% and 0.25%) and type of web reinforcement (deformed bars and welded-wire mesh). Shaking table tests were essential for assessing dynamic characteristics, such as changes in fundamental frequencies and damping factors of RC walls for low-rise housing. © 2012 Elsevier Ltd.


Carrillo J.,University Militar Nueva Granada | Carrillo J.,National Autonomous University of Mexico | Alcocer S.,National Autonomous University of Mexico
Earthquake Engineering and Structural Dynamics | Year: 2011

Shaking tables are suitable facilities to assess and validate the behavior of structures and nonstructural components under actual seismic actions. Because of the size and weight limitations of the tables, some approaches, like testing reduced-scale models or testing only the main structural components, are deemed necessary. In these cases, to comply with modeling requirements, large amount of extra-mass should be added to the specimen. Therefore, to avoid the risk of lateral instability of models, to maintain the weight of test specimens within table payload, while maintaining the amount of mass needed, an external device for transmitting the inertia forces to the models using an improved sliding system is proposed. Although friction devices for similar purposes have been developed using sliding bearings (Teflon pads or rollers), the measured coefficient of dynamic friction and the energy dissipated by friction have been very high. In order to drastically diminish the damping added to the specimen response when a friction device is used, the improved device employs a linear motion guide system (LMGS) with very low friction. Shaking table tests to collapse of reinforced concrete walls were used to evaluate the effectiveness of the proposed device. Measured dynamic friction coefficients, spectral accelerations and hysteresis loops show that friction developed in the LMGS did not add any significant amount of damping into the specimen response. Thus, the proposed device is a reliable and suitable mass-carrying sliding system (MCSS) for dynamic testing using medium-size shaking tables. © 2010 John Wiley & Sons, Ltd.


Carrillo J.,University Militar Nueva Granada | Alcocer S.M.,National Autonomous University of Mexico
Earthquake Engineering and Structural Dynamics | Year: 2012

Acceptance limits of the structural response of walls for low-rise concrete housing were developed. Proposed values are applicable within a performance-based seismic design framework. Acceptance limits are based on performance indicators of structural response-allowable story drift ratios, width of residual cracks and residual damage index, and expected damage of walls. Cracking limits were defined from parameters obtained at the unloading stage of walls (i.e., residual cracking stage). The residual cracking stage may be used for structural damage evaluation and cost estimation of structural rehabilitation after an earthquake has occurred. The performance indicators proposed herein were derived from test observations and measured response of 39 RC walls' specimens during shaking table and quasistatic testing, as well as from limiting values and results of previous studies. © 2012 John Wiley & Sons, Ltd.


Carrillo J.,University Militar Nueva Granada | Alcocer S.M.,National Autonomous University of Mexico
ACI Structural Journal | Year: 2013

In the last decade, the construction of low-rise housing made of reinforced concrete (RC) walls and slabs in Latin America has increased considerably. These box-type structures commonly have large lateral stiffness and strength, thus exhibiting low lateral displacements and shear forces demands. The low level of seismic response has prompted designers to use concrete strengths of 15 to 20 MPa (2175 to 2900 psi), as well as of 100 mm (4 in.) thick walls with web steel reinforcement ratios smaller than the minimum prescribed by most design codes. Considering these particular wall characteristics, design requirements in current codes are not directly applicable. Moreover, a blind application of current requirements may lead to an unjustifiable excessive cost of a housing unit, especially because of the web steel ratio required. To improve design methods for this type of construction, a behavioral model and equations capable of estimating the peak shear strength of walls for low-rise housing were developed and calibrated from test results. The experimental program included quasi-static and shake-table tests of walls with different height-to-length ratios (hw/lw) and walls with openings. Variables studied were the type of concrete, web steel ratio, and type of web reinforcement. Statistical analysis of the ratios between predicted and measured shear forces demonstrated that the proposed model is a suitable design tool that may be adopted for design and evaluation guidelines and codes.Copyright © 2013, American Concrete Institute. All rights reserved.


Carrillo J.,University Militar Nueva Granada
Earthquake Engineering and Structural Dynamics | Year: 2015

Widely used damage indices, such as ductility and drift ratios, do not account for the influences of the duration of strong shaking, the cumulative inelastic deformation or energy dissipation in structures. In addition, the formulation and application of most damage indices have until now been based primarily on flexural modes of failure. However, evidence from earthquakes suggests that shear failure or combined shear-flexure behavior is responsible for a large proportion of failures. Empirical considerations have been made in this paper for evaluating structural damage of low-rise RC walls under earthquake ground motions by means of a new energy-based low-cycle fatigue damage index. The proposed empirical damage index is based on the results of an experimental program that comprised six shake table tests of RC solid walls and walls with openings; results of six companion walls tested under QS-cyclic loading were used for comparison purposes. Variables studied were the wall geometry, type of concrete, web shear steel ratio, type of web shear reinforcement, and testing method. The index correlates the stiffness degradation and the destructiveness of the earthquake in terms of the duration and intensity of the ground motions. The stiffness degradation model considers simultaneously the increment of damage associated to the low-cycle fatigue, energy dissipation, and the cumulative cyclic parameters, such as displacement demand and hysteretic energy dissipated. © 2014 John Wiley & Sons, Ltd.


Patent
University Militar Nueva Granada | Date: 2014-02-27

An orthosis according to definition is an external support or other device applied to the body to change the functional or structural aspects of the neuromuscular skeletal system. The device which has been designed and described in detail above is intended to reduce the loads which surgeons have to support on their shoulders and legs during long periods of time during which they are engaged in surgical operations and therefore to reduce the risk that they will suffer lesions such as disc hernias, varicose veins, and pain, among others, through the use of mechatronic systems which facilitate their use and allow greater freedom of movement.


Patent
University Militar Nueva Granada | Date: 2014-03-14

The present invention relates to an automatic stimulator based on vibrations for cell cultures, fulfilling the function of activating the proliferation of osteoprogenitor cells and of activating the expression of the genes involved in the process of cell differentiation toward the osteogenic line. This effect is produced in the cells by the application of mechanical vibrational load. In this respect, the operation of the stimulator of the present invention comprises a system incorporating an actuator of mechanical type, controlled and regulated according to the specific requirements defined by the user. The actuator is the source of the vibrations which will be applied upon the flasks containing the cell cultures. The automatic stimulator for cell cultures is characterized by being controllable and programmable from a computer through the storage of routines of stimulation and repose, with programming of intensity of the load graduated in G (gravitational) units, being repeated in an automatic manner a number of times determined by the user, it being appropriate for performing routines in the laboratory.

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