Papers by daniel alberto Rojas
Tecnologia y Ciencias del Agua, 2015
En general, se ha encontrado que los humedales construidos son efectivos en diferentes grados par... more En general, se ha encontrado que los humedales construidos son efectivos en diferentes grados para la remocion de farmacos; sin embargo, existen casos como el de la carbamazepina (CBZ), cuyas eficiencias de remocion reportadas han sido muy bajas. El objetivo de este estudio fue evaluar las eficiencias de remocion masica de dicho farmaco en tres sistemas de humedales hibridos con dos etapas de tratamiento, incluyendo humedales subsuperficiales de flujo horizontal (HSSFH), humedales subsuperficiales de flujo vertical (HSSFV) y lagunas de estabilizacion (LE). Las tres diferentes configuraciones fueron HSSFH-LE, HSSFHHSSFV y HSSFV-HSSFH, denominados como SI, SII y SIII, respectivamente. Ademas, se realizaron mediciones in situ de OD, Eh, pH, CE, ET y temperatura, con el proposito de conocer en que condiciones operaban dichos sistemas. Los resultados revelaron diferencias significativas (p < 0.05) en la eficiencias de remocion de los sistemas hibridos, con un promedio de 60 ± 4.45% pa...
International Journal of Gastronomy and Food Science, 2021
Revista Nova, 2020
A test bench allows measuring and recording the operating parameters of the engines. The need to ... more A test bench allows measuring and recording the operating parameters of the engines. The need to develop such a device emerged in order to know the operation of the Desert Aircraft 85 cm3 two-stroke engine, which is commonly
UNED Research Journal, 2013
From extensive research on the phenomenom of “simpatía”, known as a relationship or an affinity b... more From extensive research on the phenomenom of “simpatía”, known as a relationship or an affinity between people or things in which whatever affects one correspondingly affects the other, in Latin American countries, many characteristics, such as friendliness and a positive attitude, have been identified. However, despite such positive attitudes, very few studies measured levels of happiness and satisfaction in these communities, specifically Costa Rica. This study measured happiness levels during March-April 2012 in San Ramón, Costa Rica. Created questionnaires measuring happiness levels were distributed to 197 participants (104 M, 92 F, 1 Unknown). A validated questionnaire showed homogeneity to our created questionnaire (P<0,0001). Mean responses relating happiness to “good health” (=4,73) and “family communication” (= 4,58) were greater than responses of “quantity of money made each month” (= 3,49) or “owning material goods” (= 3,49) (P<0,05). Mean responses of “having a...
The Analyst, 2017
Correction for ‘Microchip in situ electrosynthesis of silver metallic oxide clusters for ultra-FA... more Correction for ‘Microchip in situ electrosynthesis of silver metallic oxide clusters for ultra-FAST detection of galactose in galactosemic newborns’ urine samples by Laura García-Carmona et al., Analyst, 2016, 141, 6002–6007.
Studies in Informatics and Control, 2014
In this paper it is presented an integration of algorithms that permits maps construction and nav... more In this paper it is presented an integration of algorithms that permits maps construction and navigation of mobile robots. Simultaneous Localization and Mapping (SLAM) algorithm is used based on FastSLAM method. Navigation system is based on Vector Field Histogram algorithm to avoid obstacle and a spiral way trajectory method. Up to three different complex simulation maps have been used to evaluate the system.
OASIS, 2016
La Alianza del Pacífico se instituyó como una propuesta de integración profunda entre Chile, Colo... more La Alianza del Pacífico se instituyó como una propuesta de integración profunda entre Chile, Colombia, México y Perú. La pregunta que se plantea en este trabajo es ¿cuál de los enfoques del regionalismo en América Latina es el más idóneo para caracterizar teóricamente la iniciativa de la Alianza del Pacífico? En este sentido, se exponen los conceptos de regionalismo abierto y regionalismo estratégico para caracterizar esta iniciativa, y se resaltan sus límites a partir de evidencia empírica. El trabajo concluye que los conceptos de regionalismo que dan mayor énfasis a las dinámicas comerciales no son suficientes para comprender el funcionamiento y desempeño actual de la Alianza del Pacífico, por lo que se introduce un enfoque analítico complementario, el cual responde a dinámicas globales de largo plazo.
Dyna, Apr 1, 2011
Effective control of rougher fl otation is important because a small increase in recovery results... more Effective control of rougher fl otation is important because a small increase in recovery results in a signifi cant economic benefi t. Although many fl otation control strategies have been proposed and implemented over the years, none of them incorporate concentrate grade measurements at intermediate cells because these data are not usually available. On the other hand, there is much research on characterizing concentrate froth on the cell surface by image processing in order to extract information on froth color, bubble size, and speed that can then be used for developing expert control strategies, and some works have shown the possibility of estimating the concentrate grade. This work presents two multivariable model based predictive control (MPC) strategies for a rougher circuit. The fi rst strategy is based only on general tailings and concentrate grade measurements while the second one includes, beside these data, the intermediate cell grade estimates. Both strategies are compared with a fi xed control strategy. Simulation tests show that the recovery can increase by 1.7%, compared to the fi xed control strategy.
Educación y Educadores, 2014
Esta investigación cuantifi ca las diferencias de impacto sobre la situación laboral de los egres... more Esta investigación cuantifi ca las diferencias de impacto sobre la situación laboral de los egresados a raíz de su titulación entre las modalidades presencial y virtual, de un Programa de Educación Tecnológica Superior. Se aplicó un cuestionario a 102 egresados de una institución de educación superior colombiana (51 de cada modalidad bajo estudio), en el programa de Formación Tec
Biological Research, 2004
Although there is extensive literature about the effects of stimulants on sustained attention tas... more Although there is extensive literature about the effects of stimulants on sustained attention tasks in attentional deficit/hyperactivity disorder (ADHD), little is known about the effect of these drugs on other attentional tasks involving different neural systems. In this study we measured the effect of stimulants on ADHD children, both in the electroencephalographic (EEG) activity during sustained attentional tasks and in psychometric performance during selective attentional tasks. These tasks are known to rely on different cortical networks. Our results in children medicated with 10 mg of d-amphetamine administered 60 min before the study indicate (i) a significant increase in amplitude but not latency of the P300 component of the event-related potential (ERP) during the sustained attentional task and (ii) a significant improvement in the reaction times and correct responses in the selective attentional task. In addition to supporting the use of stimulants in children with attentional deficit/hyperactivity disorder, these results show a multifocal activity improvement of cortical structures linked to dopamine, and interestingly, to attention. All these analyses are framed in a wider study of diverse attentional functions in this syndrome.
Annales Geophysicae, 1997
We study the annual frequency of occurrence of intense geomagnetic storms (Dst < A100 nT) through... more We study the annual frequency of occurrence of intense geomagnetic storms (Dst < A100 nT) throughout the solar activity cycle for the last three cycles and ®nd that it shows dierent structures. In cycles 20 and 22 it peaks during the ascending phase, near sunspot maximum. During cycle 21, however, there is one peak in the ascending phase and a second, higher, peak in the descending phase separated by a minimum of storm occurrence during 1980, the sunspot maximum. We compare the solar cycle distribution of storms with the corresponding evolution of coronal mass ejections and¯ares. We ®nd that, as the frequency of occurrence of coronal mass ejections seems to follow very closely the evolution of the sunspot number, it does not reproduce the storm pro®les. The temporal distribution of¯ares varies from that of sunspots and is more in agreement with the distribution of intense geomagnetic storms, but¯ares show a maximum at every sunspot maximum and cannot then explain the small number of intense storms in 1980. In a previous study we demonstrated that, in most cases, the occurrence of intense geomagnetic storms is associated with a¯aring event in an active region located near a coronal hole. In this work we study the spatial relationship between active regions and coronal holes for solar cycles 21 and 22 and ®nd that it also shows dierent temporal evolution in each cycle in accordance with the occurrence of strong geomagnetic storms; although there were many active regions during 1980, most of the time they were far from coronal holes. We analyse in detail the situation for the intense geomagnetic storms in 1980 and show that, in every case, they were associated with a¯are in one of the few active regions adjacent to a coronal hole.
The purpose of this work was to evaluate different conditions and culture parameters for the in v... more The purpose of this work was to evaluate different conditions and culture parameters for the in vitro establishment and multiplication of Hylocereus purpusii. Seeds were used as plant material and a workflow was developed as an alternative for the propagation and recovery of this species in danger of extinction. In the establishment phase, the best result was obtained in the treatment with 1% NaOCl for 15 minutes achieving a 90% of germinated seeds and a final 77.7% of in vitro established plants. In the multiplication phase when combining 8.88 µM 6-BAP with different concentrations of IAA, a significant increment in the length of the shoots was observed with respect to the control (no addition of IAA). A combination of 8.88 µM 6-BAP with 3.42 µM IAA was selected as the best multiplication condition reaching a multiplication rate of 8.8. In the acclimatization phase, after two months of culture in ex vitro conditions, the survival was higher than 98% and after six months of growth, the plants were transplanted to field.
Albert Einstein (Zurich 1879-Princeton 1955) Presentaba en 1916 Sobre la teoría de la relatividad... more Albert Einstein (Zurich 1879-Princeton 1955) Presentaba en 1916 Sobre la teoría de la relatividad especial y general con las siguientes palabras: «El presente librito pretende dar una idea lo más exacta posible de la teoría de la relatividad, pensando en aquellas personas que, ...
Enlace, 2008
Services' provision involves a number of factors, among which stands out the information, so the ... more Services' provision involves a number of factors, among which stands out the information, so the perception of its quality by the client must be assessed as part of the service. The present study shows a model for evaluating the quality of information delivered to customers in services and its corresponding instrument. This model is validated through its application in the medical service of a social welfare institute in a Venezuelan university. The investigation is a non-experimental design type transactional. The population is teachers affiliated with the institute. The sample is determined using a stratified sampling proportional. The variable quality of the information delivered to customers is formed by the sub-dimensional delivery, accessibility and operational issues. The results are made up of an operational model for assessing the quality of corporate information delivered to customer in service, its own instrument of measurement, and a diagnosis resulting from the application of this instrument, which shows that the information studied, presents a medium quality. The results of information's diagnosis allow design strategies to improve the quality of information provided to those affiliated in the medical services. Finally, we conclude that the proposed model evaluation is a contribution to the study of quality in information services.
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Papers by daniel alberto Rojas