Modelo numérico para el estudio dinámico de un rotor con eje agrietado

En este trabajo se presenta un análisis teórico de la dinámica de un sistema rotor-descansos con una grieta transversal en su eje. Con el objeto de poder utilizar programas estándares de elementos finitos se deduce utilizando los principios de la mecánica de fractura, la matriz de rigidez para un elemento de eje con una grieta transversal que se abre y cierra. Los cambios de rigidez generados por el respiro de la grieta son expresados a través de una función armónica. Se analiza la influencia de la grieta en las vibraciones transversales y longitudinales de un rotor sencillo perfectamente balanceado. Los resultados obtenidos son comparados con resultados de trabajos teóricos y experimentales publicados anteriormente. Se muestra cómo las componentes espectrales de los desplazamientos vibratorios 1 0, 2 R y 3 R varían con la velocidad del rotor. Esto es un buen indicador a usar para diagnosticar un eje agrietado en los sistemas de monitoreo de vibraciones.A theoretical analysis of the dynamics of a rotor-bearing system with a transversely cracked shaft is presented. In order to model the system for standard finite element method, the stiffness matrix of a shaft element with an opening/closing crack is derived based on fracture mechanics. The change of stiffness due to the crack breathing is expressed through an harmonica function. The influence of crack on the transversal and longitudinal vibration of a simple balanced rotor is analyzed. Results obtained by this analysis procedure are compared with previous analytical and experimental works published. From the FFT analysis of the displacement responses, it is shown how the 1 R, 2 R and 3 R components excited varied with speed rotor. This provides good indicator for diagnosing a cracked shaft from a vibration monitoring system.Peer Reviewe

Estudio de la densidad mineral ósea mediante osteosonografía en niños y adolescentes sanos: valores de normalidad

Osteoporosis is a frequent health problem in adults. Optimization of bone mass acquisition during childhood and adolescence may play a major role in the prevention of this disease. Osteosonography is a recent technique for measuring bone mineralization without exposing the patient to radiation. OBJECTIVES: To measure bone mineral density using osteosonography in healthy Spanish Caucasian children and adolescents in order to determine normal values. METHODS: We performed a cross sectional study of 829 healthy child and adolescent volunteers (360 girls and 469 boys) randomly selected from the urban area of Pamplona in Navarre (Spain). Ages ranged from 6 to 18 years. ADBM Sonic 1200 ultrasound densitometer from IGEA was used. Daily calcium dietary intake and amount of physical activity were recorded. RESULTS: Cross sectional standards for Ad-SOS are presented. Ad-SOS did not significantly change between the ages of 6 and 9 years in girls or until the age of 10 years in boys. From the ages of 10 to 14 years, Ad-SOS values were higher in girls than in boys. After the age of 14 years, no significant differences were found. No correlation was found between calcium dietary intake, amount of physical exercise or bone mineralization values. CONCLUSIONS: Measurement of Ad-SOS by osteosonography is an easy, fast and inexpensive method for measuring bone mineral density in children and adolescents without exposing them to radiation. It can be used in the pediatric population to detect early alterations in bone mineralization

Adopting an African Standpoint in HCI4D::A Provocation

While studies in HCI4D have been advanced by the shift of perspective from developmental studies to a range of other discourses, current analytical concepts for understanding the sociality of society in Africa have arguably led to some misinterpretations of the place of technology. This provocation suggests that an ‘African Standpoint’ based on a combination of various standpoint positionalities and the Wittgensteinian approach of Winch can offer conceptual and analytical sensitivities for articulating social relations, transnational engagements and the conceptualisation of technological innovation. This provides an approach for seeing and accounting for things as they are – right here, right there and right now – and not some idealised conception of an African reality

Exploring the Viability of Offering the Bachelor of Library and Information Science Program at Central Luzon State University, Philippines

The Bachelor of Library and Information Science (BLIS) program in the Philippines provides excellent employability due to its high demand in academia and other sectors. This study aimed to determine the viability of offering the Bachelor of Library and Information Science program at Central Luzon State University. The survey specifically sought to determine grade 11 students\u27 interest in enrolling in the program as well as its market employability in the academic sector in the region. Data were collected using a survey questionnaire from three public and three private neighboring high schools of Central Luzon State University as well as Google forms for higher education institutions. The data were described using the frequency count and percentage. SWOT analysis was also used to evaluate the institution\u27s advantage and capability to offer the program, as well as the program\u27s potential and direction. Findings present that the program is viable and the institution can sustain it. However, there are areas that should be strengthened and improved, as well as potential threats to the program\u27s continuation, such as a lack of awareness and poor performance on board examinations

Characters of the Stephanian-Permian Bronchales basin and the tourmalinization associated to calc-alkaline rhyolites (Teruel Province)

[Resumen] La turmalinización que afecta a riolitas calco-alcalinas presentes en la fosa transtensional de Bronchales, con edad Autuniense, destaca por el elevado contenido en B (0.87 O/o de promedio). Esta mineralización muestra un enriqueciIl\iento de HREE y un empobrecimiento en LREE debido a que el fluido mineralizante (rico en F) pudo ejercer una función acomplejante para estos elementos y, también, con carácter selectivo, para As, Sn, Sb y Bi.[Abstract] Calc-alkaline rhyolites of Bronchales transtensional basin (Autunian age) are affected by a tourmalinization process. Tourmalinized rhyolites with 0.87 O/o ofboron as average value show As, Sb, Sn and Bi increments over nontourmalinized ones, as well as important enrichments of HREE over LREE possibly because tourmalinization fluids were enriched in complexing agents (i.e .F)

Serendipitous discovery of RR Lyrae stars in the Leo V ultra-faint galaxy

During the analysis of RR Lyrae stars discovered in the High cadence Transient Survey (HiTS) taken with the Dark Energy Camera at the 4-m telescope at Cerro Tololo Inter-American Observatory, we found a group of three very distant, fundamental mode pulsator RR Lyrae (type ab). The location of these stars agrees with them belonging to the Leo V ultra-faint satellite galaxy, for which no variable stars have been reported to date. The heliocentric distance derived for Leo V based on these stars is 173 +/- 5 kpc. The pulsational properties (amplitudes and periods) of these stars locate them within the locus of the Oosterhoff II group, similar to most other ultra-faint galaxies with known RR Lyrae stars. This serendipitous discovery shows that distant RR Lyrae stars may be used to search for unknown faint stellar systems in the outskirts of the Milky Way.Comment: Accepted in ApJ Letter

Reduced Bone Mineralization in Adolescent Survivors of Malignant Bone Tumors: Comparison of Quantitative Ultrasound and Dual-Energy X-Ray Absorptiometry

To assess bone mineralization in adolescents with bone tumors at remission using quantitative digital ultrasound (QUS) and dual-energy x-ray absorptiometry (DEXA), and to compare the bone mineralization values obtained by both methods. METHODS: Patients studied were 36 adolescents (21 boys, 15 girls) who had completed treatment of a bone tumor at the University Hospital of the University of Navarra (Pamplona, Spain). QUS was performed at the distal metaphysis of the proximal phalanxes of the last four fingers of the nondominant hand. A DBM Sonic 1200 Ultrasound densitometer was used. DEXA measurements were made at the lumbar spine (vertebrae L1-L4) using the Hologic QDR 4500 W device. Calcium and vitamin D daily intake and grade of physical activity were recorded. RESULTS: Mean age at bone mineralization determination was 19.11 years. Disease-free survival was 4.97 years. Decreased bone mineralization was observed by both methods. Bone mineralization absolute values measured by QUS and DEXA were significantly correlated. The sensitivity, specificity, diagnostic accuracy, and positive and negative predictive values of QUS for predicting osteopenia were 36.4%, 80.0%, 66.7%, 44.4%, and 74.1%, respectively. Daily vitamin D intake was below the recommended dietary allowances. CONCLUSIONS: Adolescents in remission from bone tumors have low bone mineralization determined by DEXA or QUS