Metodología de cálculo de NOx en generadores de vapor que queman gas natural

Este trabajo presenta la metodología para el cálculo de emisiones de NOx en un generador de vapor de 350 ton/h quemando gas natural y se investigan los métodos de control de NOx durante la combustión. Hoy en día es uno de los principales problemas de las plantas termoeléctricas puesto que genera un alto nivel de emisiones de óxidos de nitrógeno a la atmósfera. Esta metodología consiste en la determinación de los cuatro parámetros fundamentales que intervienen en la formación de NOx y son los siguientes: coeficiente de exceso de aire en la zona de combustión activa (ZCA) ¿ZCA, la temperatura promedio de la ZCA TZCA, el flujo de calor reflejado en ZCA qrefl ZCA y el tiempo de residencia de los gases en ZCA ¿ZCA. Para poder determinar estos parámetros se tiene que considerar la composición del gas natural, la transferencia de calor en el horno, las condiciones de funcionamiento y las dimensiones del generador de vapor, entre otros factores. Los cuatro parámetros principales se sustituyen en el polinomio experimental para el combustible en cuestión y, de esta forma, se puede determinar la emisión de NOx para los métodos de combustión que se analizarán en el presente artículo: recirculación de gases, diferentes lugares de introducción de gases de recirculación, combustión a dos etapas e inyección de agua

Long-term soiling of silicon PV modules in a moderate subtropical climate

AbstractThe results of 28 silicon-based PV modules which were installed from 1981 to 1985 in a free rack configuration in the outdoor test facility of the European Solar Test Installation (ESTI) and dismantled at the end of 2014 without cleaning were analysed. The system was composed of modules with two series-connected laminates mounted in a single frame produced by the same manufacturer but using different cell layouts and cover glasses (plain glass or textured glass). The effects of long-term soiling on the PV module performance for more than 30years of outdoor exposure in a moderate subtropical climate and the influence of different cleaning methods from manual cleaning to the use of high pressure water washing were investigated. The influence of the cover glasses and the mismatch due to the particular manufacturing design were also analysed. It was observed that a manual cleaning was effective at improving the output of all the module types. However, additional high pressure water spraying on plain glass modules showed no further improvement, but showed small improvements on the textured glass modules. Overall improvements in Pmax after cleaning ranged from 3.5% to 19.4%, with an average value of 9.8% and an average improvement in Isc of 6.7% were obtained

Weak positive cloud-to-ground flashes in Northeastern Colorado

The frequency distributions of the peak magnetic field associated with the first detected return stroke of positive and negative cloud-to-ground (CG) flashes were studied using lightning data from northeastern Colorado. These data were obtained during 1985 with a medium-to-high gain network of three direction finders (DF's). The median signal strength of positive flashes was almost two times that of the negatives for flashes within 300 km of the DF's, which have an inherent detection-threshold bias that tends to discriminate against weak signals. This bias increases with range, and affects the detection of positive and negative flashes in different ways, because of the differing character of their distributions. Positive flashes appear to have a large percentage of signals clustered around very weak values that are lost to the medium-to-high gain Colorado Detection System very quickly with increasing range. The resulting median for positive signals could thus appear to be much larger than the median for negative signals, which are more clustered around intermediate values. When only flashes very close to the DF's are considered, however, the two distributions have almost identical medians. The large percentage of weak positive signals detected close to the DF's has not been explored previously. They have been suggested to come from intracloud discharges and thus are improperly classified as CG flashes. Evidence in hand, points to their being real positive, albeit weak CG flashes. Whether or not they are real positive ground flashes, it is important to be aware of their presence in data from magnetic DF networks

Transvaginal color Doppler assessment of venous flow in adnexal masses

Objective To analyze the usefulness of transvaginal color Doppler assessment of venous flow in the differential diagnosis of adnexal masses. Material and Methods Ninety-one consecutive patients (mean age: 46.6 years, range: 16–81 years) diagnosed as having an adnexal mass were evaluated by transvaginal color Doppler sonography prior to surgery. Color Doppler was used to detect and analyze the flow velocity waveform from arterial and venous blood flow within the tumor. For arterial signals the resistance index and peak systolic velocity, and for veins the maximum venous flow velocity, were calculated. Receiver operator characteristic curves were plotted to determine the best venous flow velocity cut-off. According to our previous study using arterial Doppler, a tumor was considered as malignant when flow was detected and the lowest resistance index was ≤ 0.45. Using venous Doppler a mass was considered as malignant when flow was detected and the venous flow velocity was ≥ the best cut-off found on the receiver operator characteristic curve. Definitive histopathological diagnosis was obtained in all cases. Sensitivity, specificity, positive predictive value and negative predictive value for B-mode morphology (evaluation performed according to Sassone’s scoring system), arterial Doppler, venous Doppler, and a combination of both arterial and venous Doppler were calculated. Results Twenty-five masses (27.5%) were malignant and 66 (72.5%) benign. Arterial and venous flow was found more frequently in malignant than in benign masses (92% vs. 41% (P < 0.001) and 72% vs. 21% (P < 0.001), respectively). The resistance index was significantly lower in malignant tumors (0.42 vs. 0.60, P = 0.0003). No differences were found in peak systolic velocity. Venous flow velocity was significantly higher in malignant masses (18.1 cm/s vs. 8.9 cm/s, P = 0.0006). The best cut-off of venous flow velocity was 10 cm/s. Sensitivity, specificity, positive predictive value and negative predictive value for morphology, arterial Doppler, venous Doppler, and the combination of both arterial and venous Doppler were 92%, 71%, 45%, 96%; 76%, 95%, 87%, 91%; 68%, 94%, 81%, 89%; and 88%, 91%, 79%, 95%, respectively. Conclusions Our results indicate that preoperative evaluation by venous flow assessment of adnexal masses may be useful to discriminate between malignant and benign tumors

ACUTE EFFECTS OF SMALL CHANGES IN BICYCLE SADDLE HEIGHT ON PEDALLING COORDINATION

The purpose of this study was to analyse the acute effects of small changes in bicycle saddle height on pedalling coordination, using vector coding analysis. Lower extremity kinematic data were collected from ten well-trained cyclists while they pedalled at three different saddle heights in random order: preferred, 2% higher and 2% lower than preferred position. A modified vector coding technique and circular statistics were used to quantify coordination for selected hip-knee, hip-ankle, and knee-ankle joint couplings. The results indicate that modifications in saddle height produced moderate alterations in the frequency of movement patterns, which were not enough to alter the classification of coordination. The small modifications observed were in the direction of increasing the frequency of the proximal coordinative pattern as the saddle height decreased

THE INFLUENCE OF CYCLISTS’ COMPETITIVE LEVEL AND EXERCISE INTENSITY ON CRANK TORQUE VARIABILITY DURING PEDALLING

The purpose of this study was to analyse the influence of competitive level and pedalling intensity on crank torque variability. Seventy-two cyclists (Club, Elite, Professional) pedalled at 200, 250 and 300 W on a cycle ergometer that recorded crank torque. Multiple-trial variability (average standard deviation) and complexity (Sample Entropy) analyses were applied. Both competitive level and pedalling intensity showed a significant effect on Sample Entropy values of crank torque, with a significant interaction between the two factors, while average standard deviation was only affected by pedalling intensity. In conclusion, pedalling intensity had an effect on both crank torque multiple-trial variability and complexity, while the last has shown a bigger potential for fine discrimination between performance levels in cyclists

ACUTE EFFECTS OF SMALL CHANGES IN CRANK LENGTH ON TORQUE WAVEFORM DURING SUBMAXIMAL PEDALLING

The purpose of the present study was to evaluate the acute effects of small changes in crank-arm length and pedalling power on crank torque-angle profile during seated cycling. Twelve amateur cyclists participated and performed 12 sets of 5-min submaximal pedalling on a special cycle ergometer (4 intensities x 3 crank lengths). Principal Component Analysis technique was used to analyse ten crank torque-angle curves of the right leg. A longer crank increased the crank torque of the front leg (30-125º) in order to lift the rear leg (200-320º), contrary to the effect of increasing pedalling power. Furthermore, pedalling with the longest crank required higher torque values after reaching peak torque (110-170º) compared to the shortest ones. In conclusion, contrary to the lore, a longer crank requires a higher mechanical effort compared to a shorter crank for pedalling at the same intensity

Influencia de las Relaciones Interpersonales en los resultados deportivos de los equipos de Voleibol y Baloncesto masculinos y femeninos y Fútbol de la UNAN CUR Matagalpa en el año 2005

Este trabajo estuvo dirigido al estudio de las relaciones interpersonales de los equipos del Basketball, Volleyball, masculino y femenino, como también al equipo de Football masculino de UNAN CUR MATAGALPA, durante el año 2005 y la influencia de esta en los resultados deportivos. Este estudio permitió conocer a través de los test aplicados a los 55 atletas, el nivel de sus relaciones dentro del conjunto deportivo donde se denota la influencia positiva de estas relaciones dentro de los resultados competitivos. La investigación se aplico desde el inicio del proceso de entrenamiento y la composición de estos equipos en su proceso de preparación con vista a participar en las distintas competencias universitarias. Los test estuvieron conformados con contenidos relativos a la composición de los equipos, características de las edades, elementos de juego, y de convivencia social. Los resultados muestran entre los integrantes de los equipos que los atletas se destacan ante el colectivo tanto en los diferentes momentos de competencia como de la vida social. También a través del test sociométrico y del test de liderazgo se pudo llegar a la conclusión de que son los líderes democráticos con características universales apoyados con altos por cientos de popularidad por los atletas. Todos estos por sus grados de experiencias dentro y fuera del juego. No existe ningún componente del grupo rechazado sino que las características son de aislados que no representan ningún grado de conflictos dentro de las relaciones interpersonales de los equipo