Papers by GERMAN DARIO OSPINA ROJAS
This paper uses a Simulated Annealing algorithm for training an Artificial Neural Network. The ef... more This paper uses a Simulated Annealing algorithm for training an Artificial Neural Network. The efficiency of this algorithm is testing using two well know benchmark problems. Results are compared with BackPropagation algorithm and they show how this technique can resolve no-linear problem with this technique.
Temas Para El Debate, 2009
Uno de cada seis seres humanos sufre hambre cronica, en un mundo en el que hay alimentos suficien... more Uno de cada seis seres humanos sufre hambre cronica, en un mundo en el que hay alimentos suficientes para cubrir las necesidades de todos los habitantes del Planeta. El hambre en estos momentos es sobre todo una cuestion de pobreza y no de produccion de alimentos. Pero en un Planeta cuya poblacion se estima que crecera hasta los 9.100 millones en el horizonte del ano 2050, el aumento de la produccion agricola seguira siendo primordial para poder erradicar el hambre.
Economics Working Papers, 1993
Revista Universidad Eafit, Aug 28, 2012
Colombia Forestal, 1992
Clasificaion de Sitio y factores que influyen en el crecimiento de Acacia decurrens en la cuenca ... more Clasificaion de Sitio y factores que influyen en el crecimiento de Acacia decurrens en la cuenca del rio Checua-Cundinamarca
Journal of Molecular Structure: THEOCHEM, 2005
Molecular Dynamics Simulations of the shell dynamics and normal mode analysis (NMA) are carried o... more Molecular Dynamics Simulations of the shell dynamics and normal mode analysis (NMA) are carried out to study Rydberg photoexcitation of NO in Xe and Kr solids. In the case of the NO doped Kr system we have completed a previous study on shell dynamics by focusing only on the NMA, however, in the case of the NO doped Xe system we have carried out both studies: shell dynamics and NMA. For this purpose, we have used fitted Lennard-Jones potential parameters for NO(A 2 S C)-Kr and NO(A 2 S C)-Xe interactions since they have not been reported in literature. These parameters were fitted taking into account the match of simulation results to the available spectroscopic data. The dynamics of the Xe-NO matrix yielded a great dispersion in the trajectories and a slower medium response with respect to Kr-NO matrix. The NMA have allowed us to explain the immediate shell dynamics after photoexcitation, showing the validity of harmonic approximation of potentials. The results are shown comparatively with the rest of the studied matrices (Ar-NO and Ne-NO).
The Journal of Physical Chemistry A, 2003
The absorption and emission spectra of the 3P1-1 S0 transition of a Hg atom embedded in solid arg... more The absorption and emission spectra of the 3P1-1 S0 transition of a Hg atom embedded in solid argon have been simulated using the molecular dynamics with quantum transitions algorithm to consider the nonadiabatic transitions between the three adiabatic states. The ...
physica status solidi (b), 2005
ABSTRACT We study the dynamics of structural relaxation, induced by excitation of an NO molecule,... more ABSTRACT We study the dynamics of structural relaxation, induced by excitation of an NO molecule, to its A2Σ+ Rydberg state in rare gas (RG) solids. Classical molecular dynamics simulations were carried out to describe the dynamics of the cage, formed by RG atoms surrounding the NO molecule. The results show a behaviour characterized by an impulsive expansion of the cage radius at short times, followed by a complex oscillatory pattern around the average NO–RG distance of ∼3.9 Å for NO(A2Σ+)–Ne, ∼4 Å for NO(A2Σ+)–Ar, ∼4.24 Å for NO(A2Σ+)–Kr, and ∼4.55 Å for NO(A2Σ+)–Xe. The size of the cage radius in the Rydberg state increases from ∼5% (Xe) to ∼25% (Ne) when compared with the initial cage radius. The experimental work showed a recurrence time of ∼1.4 ps (Ne) and ∼0.8 ps (Ar), while in our theoretical results we obtained ∼2 ps (Ne) and 0.8 ps (Ar), which is in good agreement with experimental results. The molecular dynamics simulations of the higher shells reveal a high degree of directionality of the propagation of the deformation in the solids, except in the NO–Ne solid system. We explained the dependences of the different behaviour in each system. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
The Journal of Chemical Physics, 2001
ABSTRACT
The Journal of Chemical Physics, 2012
Within a generalized Langevin framework for open quantum systems, the cyclic evolution of a twole... more Within a generalized Langevin framework for open quantum systems, the cyclic evolution of a twolevel system is analyzed in terms of the geometric phase extended to dissipative systems for Ohmic friction. This proposal is applied to the dynamics of chiral molecules where the tunneling and parity violating effects are competing. The effect of different system-bath coupling functions in the dissipated energy is shown to be crucial to understand the behavior of the geometric phase as well as the decoherence displayed by the corresponding interference patterns.
The European Physical Journal D - Atomic, Molecular and Optical Physics, 2003
In the present work we studied the immediate medium response to the excitation to the A(3sσ) Rydb... more In the present work we studied the immediate medium response to the excitation to the A(3sσ) Rydberg state of NO impurity embedded in a solid Kr matrix. The excitation, extended over a large range of the lattice was investigated by classical molecular dynamics simulations. This has been done using Lennard-Jones pair potentials from the literature for the NO(X 2 Π)−Kr interactions and fitted in this work for the NO(A 2 Σ +)−Kr ones, since these last have not been reported in literature. Thus is obtained the first shell response to the excitation of the impurity (approximately the first 2 ps) as well as the response of the continuous shells up to the 10th one. This first response of the first shell is compared to that for similar systems (Ne and Ar matrixes doped with NO). Therefore some theoretical conclusions are drawn. The results indicate the inertial character of the response propagation throughout the surrounding medium and the high degree of nuclear coherence at short times. PACS. 34.30.+h Intramolecular energy transfer; intramolecular dynamics; dynamics of van der Waals molecules-02.70.Ns Molecular dynamics and particle methods-31.70.Ks Molecular solids
Chemical Physics Letters, 2010
The femtosecond response of NO-doped rare gas matrices is studied within a stochastic Langevin th... more The femtosecond response of NO-doped rare gas matrices is studied within a stochastic Langevin theoretical framework. As is shown, a simple damped harmonic oscillator model can describe properly the absorption and emission line shapes associated with the NO (A 2 Σ + ←→ X 2 Π) electronic transitions inside these media as well as the matrix first-solvation shell response in a process with two timescales, finding a fairly good agreement with available experimental data. This approach thus constitutes an alternative and complementary way to analyze the structural relaxation dynamics of systems in liquids and solids, leading to a better understanding of the underlying physics.
Chemical Physics Letters, 2006
We examine two standard methods to incorporate quantum effects in classical molecular dynamics si... more We examine two standard methods to incorporate quantum effects in classical molecular dynamics simulations of quantum solids. It is shown that thermal harmonic quantum correction fails to generate a reliable structure of solid neon, while augmenting the ...
Chemical Physics Letters, 2006
We examine the performance of recent potential energy surfaces for the C2Σ+ state of LiAr, obtain... more We examine the performance of recent potential energy surfaces for the C2Σ+ state of LiAr, obtained through pseudopotential and configuration interaction calculations, to describe the relaxation dynamics of argon matrices doped with lithium after excitation to the first Rydberg state of the diatomic molecule. Our results show that the absorption band and the dynamical behavior of the system are quite
Chemical Physics Letters, 2002
The dynamics of electron 'bubble' formation upon excitation of the A(3sr) Rydberg orbital of NO i... more The dynamics of electron 'bubble' formation upon excitation of the A(3sr) Rydberg orbital of NO in solid Ne was investigated by means of femtosecond pump-probe spectroscopy. We observe an ultrafast expansion of the bubble, followed by a vibrational recurrence in $1.4 ps. The overall dynamics is slower than in the heavier argon solid. Molecular dynamics simulations show that this results from the collective motion of several shells around the excited impurity, as a result of the nature of the excited NOA-Ne and the Ne-Ne potentials. Quantum effects play a negligible role in the dynamics.
Birth, 2008
Hemorrhage and hypertensive disorders are major contributors to death after delivery in developin... more Hemorrhage and hypertensive disorders are major contributors to death after delivery in developing countries. The GIRMMAHP Initiative was designed to describe the actual delivery care in five Latin American countries and to educate and motivate clinical staff at 17 hospitals with the purpose of implementing their own clinical practice guidelines to prevent postpartum hemorrhage. A multicountry education intervention was developed in four consecutive stages, using two analyses: (a) an observational study of the clinical records in eight teaching and nine nonteaching hospitals and (b) a study of the long-term changes measured 12 months after completion of an education intervention and writing a local clinical guideline. Data from 2,247 pregnant women showed that only 23.3 percent had an active management of the third stage of labor and that 22.7 percent received no prenatal care visit. These data were used to prepare local clinical practice guidelines in each participant hospital. The proportion of active management increased to 72.6 percent of deliveries at 3 months and 58.7 percent 1 year later. Use of oxytocin during the third stage of labor increased to 85.9 percent of included deliveries. The proportion of women who had postpartum hemorrhage decreased from 12.7 percent at baseline to 5 percent at 1 year after the intervention. An education intervention and discussion of actual clinical practice problems with health professionals and their involvement in drafting clinical guidelines helped improve health care quality and practitioners' adherence to these guidelines.
Uploads
Papers by GERMAN DARIO OSPINA ROJAS