The Universidad Nacional de Colombia , also called UNAL or just UN, is a public, national, coeducational, research university, located primarily in Bogotá, Medellín, Manizales and Palmira, Colombia. Established in 1867 by an act of the Congress of Colombia, the university is the largest higher education institution of the country with more than 44,000 students, the largest number of graduated professionals per year, and number of academic programmes at undergraduate and postgraduate levels, with 423 academic programmes, which includes 94 graduate diplomas, 61 Academic specializations, 38 medical specialties, 131 Master's degrees, and 46 doctorates. It is also one of the few universities that employs post-doctorate fellows in the country. Approximately 40,000 students are studying for an undergraduate degree and 4,000 for a graduate degree.The university is a member of the Association of Colombian Universities , the Iberoamerican Association of Postgraduate Universities , and the Iberoamerican University Network Universia. Along with Antioquia and Valle universities, it conforms what is known as the Golden Triangle of higher education in Colombia, being among the most selective and competitive universities in the country. A study by Universia found it to be the Colombian university producing the largest number of scientific papers published in peer-refereed publications in 2005, and the 45th most prolific in Latin America. Furthermore, according to the Latinamerican Web Ranking of Universities, the National University of Colombia ranked in the first place of the country in internet presence, and among the first universities in the region. Regarding the CIVETS universities, the National University occupied the fifth place.The institution offers a wide selection of programmes in both undergraduate and graduate levels, such as medicine, nursing, dentistry, engineering, chemistry, pharmacy, mathematics, physics, geology, biology, psychology, social science, arts , philosophy, and law. Wikipedia.
Hurtado J.E.,National University of Colombia
Probabilistic Engineering Mechanics | Year: 2013
Structural and mechanical reliability analysis often face the problem that probability distributions of the input variables are known with imprecision. This latter is normally specified by intervals of variation of their parameters. Leaving aside a crude Monte Carlo simulation consisting this case in estimating the failure probability for several sets of random realizations of the input distributions, there are no parsimonious methods for solving this problem in the general case of several interval parameters per distribution. In this paper a method intended to fill this gap is proposed. It is based on a property of the reliability plot recently proposed by the author [Hurtado, Dimensionality reduction and visualization of structural reliability problems using polar features. Probabilistic Engineering Mechanics, 29 (2012) 16-31], namely the fact that the order statistics of any function of the input random variables, used for building a limit state function, is concealed in the plot. This property, which is demonstrated herein, is used for the development of numerical methods for interval or reliability analysis, as well as for their combination for the estimation of the reliability interval. The ordering property of the plot assures that the lowest and largest values of the failure probability derives from samples contained in two small sets of realizations of the input distribution parameters located in specific plot sectors. The application of the proposed methodology is illustrated with examples that demonstrate its rigorousness, simplicity and accuracy. © 2013 Elsevier Ltd.
Lemeshko V.V.,National University of Colombia
Biochimica et Biophysica Acta - Biomembranes | Year: 2014
The simplest mechanism of the generation of the mitochondrial outer membrane potential (OMP) by the VDAC (voltage-dependent anion channel)-hexokinase complex (VHC), suggested earlier, and by the VDAC-glucokinase complex (VGC), was computationally analyzed. Even at less than 4% of VDACs bound to hexokinase, the calculated OMP is high enough to trigger the electrical closure of VDACs beyond the complexes at threshold concentrations of glucose. These results confirmed our previous hypothesis that the Warburg effect is caused by the electrical closure of VDACs, leading to global restriction of the outer membrane permeability coupled to aerobic glycolysis. The model showed that the inhibition of the conductance and/or an increase in the voltage sensitivity of a relatively small fraction of VDACs by factors like tubulin potentiate the electrical closure of the remaining free VDACs. The extrusion of calcium ions from the mitochondrial intermembrane space by the generated OMP, positive inside, might increase cancer cell resistance to death. Within the VGC model, the known effect of induction of ATP release from mitochondria by accumulated glucose-6-phosphate in pancreatic beta cells might result not only of the known effect of GK dissociation from the VDAC-GK complex, but also of a decrease in the free energy of glucokinase reaction, leading to the OMP decrease and VDAC opening. We suggest that the VDAC-mediated electrical control of the mitochondrial outer membrane permeability, dependent on metabolic conditions, is a fundamental physiological mechanism of global regulation of mitochondrial functions and of cell death. © 2014 Elsevier B.V.
Lemeshko V.V.,National University of Colombia
Archives of Biochemistry and Biophysics | Year: 2014
The electrostatic interaction of polycationic peptides with negatively charged biomembranes has been recognized as the first and very important step of their selective binding to many bacteria and transformed cells. In this work we demonstrated the phenomenon of competition of some earlier designed polycationic peptides and fluorescent probes for their binding to the negatively charged inner membrane of mitochondria and to the PC/PG (9:1) liposomes. Rat liver mitochondria swelling induced by the antimicrobial polycationic peptide BTM-P1 (VAPIAKYLATALAKWALKQGFAKLKS) and by the retro-BTM-P1 was significantly diminished in the presence of 10 μM fluorescent probe safranin O. In experiments with liposomes, the polycationic peptides BTM-P1 and P7-5 (IYLATALAKWALKQGF-GG-RRRRRRR) at the concentrations of 2-3 μM completely displaced the membrane-bound fluorescent probe DiSC3(5) in a low ionic strength medium. The developed computational model allowed a mathematical description of such interactions, predicting membrane surface concentrations of bound peptides as the function of the membrane surface charge and lipid quantity in the sample, the peptide charge, hydrophobicity and concentration, the ionic strength of incubation medium and of the presence of a charged fluorescent probe used for monitoring the membrane surface potential under real-time peptide-membrane interactions. © 2014 Elsevier Inc. All rights reserved.
Herrera W.J.,National University of Colombia
Journal of physics. Condensed matter : an Institute of Physics journal | Year: 2010
This work presents a novel approach to describing spectral properties of graphene layers with well-defined edges. We microscopically analyze the boundary problem for the continuous Bogoliubov-de Gennes-Dirac equations and derive the Green functions for normal and superconducting graphene layers. Importing the idea used in tight-binding models of a microscopic hopping that couples different regions, we are able to set up and solve an algebraic Dyson equation describing a graphene-superconductor junction. For this coupled system we analytically derive the Green functions and use them to calculate the local density of states and the spatial variation of the induced pairing correlations in the normal region. Signatures of specular Andreev reflections are identified.
De La Hoz F.,National University of Colombia
Vaccine | Year: 2013
Background: In Bogotá, the Heptavalent Conjugate Vaccine (PCV7) was introduced into childhood immunization schedule since 2009. The aim of this study was to assess the changes in serotype distribution and penicillin susceptibility of Streptococcus pneumoniae isolates recovered from nasopharyngeal samples and invasive disease among children living in Bogotá, before and after PCV7 introduction. Methods: Nasopharyngeal swabs were collected from healthy children aged between 12 and 18 months of age before (years 2005-2006) and after (2011) PCV7 introduction. Identification of S. pneumoniae was performed by multiplex PCR. Serotype was determined by PCR and Quellung reaction. Susceptibility to penicillin, ceftriaxone, trimethoprim-sulfamethoxazole, chloramphenicol, tetracycline and erythromycin was evaluated. In addition, distribution of serotypes and antimicrobial susceptibility before and after vaccine introduction among invasive isolates recovered from children ≤2 years old living in Bogotá was analyzed. Results: Prevalence of pneumococcal nasopharyngeal carriage declined from 55.7% (137/246) in unvaccinated to 44.2% (87/197) (p = 0.01) in vaccinated children. The proportion of children carrying PCV7 serotypes decreased from 23.6% (58/246) to 7.6% (15/197) (p < 0.001). The decrease was counterbalanced by an increase in the proportion of non-PCV7 serotypes. The most prevalent among emerging serotypes were 15A, 15B, 15. C, 11A and 35B. Among IPD isolates, PCV7 serotypes decreased from 69.1% (235/340) in 2005/2009 to 38.0% (32/84) in 2010/2011 (p < 0.001). The increase of non-PCV7 serotypes was significant. Resistance to penicillin among invasive isolates recovered from meningitis decreased from 41.1% (30/73) in the pre-vaccine period to 14.2% (2/14) in post-vaccine period (p = 0.02). Conclusions: A decrease in the prevalence of pneumococcal nasopharyngeal carriage following the introduction of PCV7 vaccine, have been overshadowed by an important surge in the prevalence of non-PCV7 serotypes. Systematic surveillance combining nasopharyngeal carriage surveys and IPD detection could help in evaluating the impact of conjugate vaccines. © 2013 The Authors.