Combined creep and plastic analysis with numerical methods

The combination of plastic and creep analysis formulation are developed in this paper. The boundary element method and the finite element method are applied in plates in order to do the numerical analysis. This new approach is developed to combine the constitutive equation for time hardening creep and the constitutive equation for plasticity, which is based on the von Mises criterion and the Prandtl-Reuss flow. The implementation of creep strain in the formulation is achieved through domain integrals. The creep phenomenon takes place in the domain which is discretized into quadratic quadrilateral continuous and discontinuous cells. The creep analysis is applied to metals with a power law creep for the secondary creep stage. Results obtained for three models studied are compared to those published in the literature. The obtained results are in good agreement and evinced that the Boundary Element Method could be a suitable tool to deal with combined nonlinear problems

Osteotomía valgizante de tibia: estudio de dos técnicas quirúrgicas

Se evalúan clínica y radiológicamente 51 rodillas artrósicas tratadas median - te osteotomía tibial valguizante según dos técnica s diferentes con fines comparativos. En 37 rodillas se empleó la osteotomía en cúpula con fijador externo y en las restante s se practicó la técnica en cuña de sustracción. El período de seguimiento medio fue de 42.2 meses. La suma de resultados buenos y excelente s ha sido 77.9%. La osteotomía en cúpula tiene , en esta serie, un mayor índice de pérdidas de corrección, correcciones insuficientes y complicaciones, obteniendo menor porcentaje de buenos resultados. Estos se deterioran en pacientes de mayor edad y gonartrosis evolucionada. Los autores consideran la osteotomía valguizante de tibia, un tratamiento válido par a pacientes de edad no avanzada y con gonartrosis grados I y II con genu varo.Two tecniques o f high tibia l osteotom y i n fifty-one ostheoarthiti c knee s evaluate d b y roentgenographi c an d clinica l examination . I n thirty-seve n patien s a dom e shape d osteotom y wit h externa l fixatio n wa s done . I n th e rest o f case s w e performe d a wedg e osteotomy . T h e numbe r o f goo d an d excelen t results wa s 77.9%. Th e dom e osteotom y ha s i n o u r experience , a hig h rat e o f recurren t varu s angulation , malalignemen t an d othe r complications. T h e olde r grou p o f patients ha d wors e results. Th e author s recomen d th e wedg e hig h tibia l osteotom y fo r osteoarthritis an d varu s kne e i n younge r patients

La artroplastia de Neer en las fracturas complejas del húmero proximal

Se estudian los resultados obtenidos después del tratamiento agudo de una serie de 32 pacientes diagnosticados de fractura en cuatro fragmentos del húmero proximal a los que se les implantó una hemiartroplastia tipo Neer I. Se llevó a cabo una evaluación clínica-radiológica de los pacientes y para la evaluación de los resultados se aplicaron los criterios de Neer. Los resultados globales obtenidos son de un 69% entre buenos y regulares y de un 31% con resultado malo. El anclaje de las tuberosidades concreta el mayor índice de complicaciones, que junto a otras totalizan un 18% de los casos. El éxito en dicho anclaje se ha correlacionado significativamente con el resultado funcional (p=0,0019). La técnica meticulosa junto con el adecuado protocolo rehabilitador se señalan como puntos esenciales para el éxito.We study the results obtained after acute treatment of a group of 32 patients diagnosed of four-fragment fracture of the proximal humerus in whom a Neer I hemiarthroplasty was used. The patients were assessed with clinic and radiological parameters, and for the evaluation of the results Neer criteria were used. The global results obtained were 69% of good and fair and 31% of bad results. The tuberosities attachment concentrate the great complication index, that together with other complications acconist for 18% of the cases. The success of the attachment had a positive correlation with functional results (p=0.0019). A meticulous technique joined with a good rehabilitation program is pointed as essential for being successful

Matemáticas para la sociedad: una visión desde los libros de aritmética del siglo XVI

Dentro de las investigaciones en Historia de la Educación Matemática el análisis de libros antiguos utilizados para la enseñanza de las matemáticas supone una importante fuente de información. Esto se debe a que los textos antiguos ayudan a reconstruir los conceptos, a contextualizarlos y a conocer sus diversos acercamientos, a interrogarse sobre la validez de las formas de argumentar vigentes en otras épocas, y a buscar los fundamentos de las formas actuales. De la misma forma, aportan información sobre lo pedagógico: las formas de organizar y presentar el contenido, sus representaciones, las situaciones, problemas y ejercicios utilizados para explicar mejor los conceptos y métodos matemáticos (Gómez, 2001). En este sentido, el objetivo de este estudio es identificar el interés social que otorgan los autores de libros de aritmética del siglo XVI a las matemáticas, es decir, si los contenidos matemáticos presentes en las obras se pueden encontrar dentro de algún contexto cotidiano, científico, económico, militar, etc

Generalidades de la familia Filoviridae y el virus del Ébola: una actualización de sus implicaciones en la población humana

Characteristics of the family Filoviridae and the Ebola virus: an update of its implications in the human population The family Filoviridae is integrated by a group of filamentous RNA viruses that cause severe hemorrhagic fevers in primates and other mammals, including humans, mainly in the African continent. Ebolavirus, arburgrvirus and Lloviu cuevavirus are the members of this family, and their main reservoirs are bats from the family Pteropodidae. The present review describes the main characteristics of the Filoviruses, pathophysiology and epidemiology on the human population, with a focus on the Ebolavirus, a pathogen of great epidemiological importance responsible for the death of 13 293 people since 1976. The Ebola outbreak of 2014-2016 was the largest in history, with 28 652 cases, representing more than 90% of the total number of cases reported since the origin of the disease (31 685). The transmission of the virus between humans can happen directly, through ontaminated fluids, or indirectly, by parenteral transmission and fomites. The incubation period ranges from 2 to 21 days and the symptomatology is divided in four phases: a febrile phase with nonspecific symptoms, a phase characterized by gastrointestinal symptoms, and two with the presence of critical symptoms. Although there is no specific treatment for the Ebola virus disease, the development of potential vaccines is currently underway, and some have showed positive results in animal models. This could lead to the appearance of an effective treatment that increases the survival of infected patients, and better epidemiological control

Germinación De Semillas De Asclepias Subulata En Condiciones De Casa Sombra Utilizando Ácido Giberélico

The objective of this work was to evaluate the use of gibberellic acid (GA3) in the seed germination of Asclepias subulata Decne., plant of the wild flora of the Sonoran Desert of interest for reforestation, industry and medicinal use. Since there is no information about their domestication, it is of fundamental importance to carry out germination tests to ensure their propagation, given the low germination percentage that this species presents. Seeds of A. subulata were collected in the Sonoran Desert, within the area known as Cerro del Bachoco. Six concentrations of gibberellic acid (GA3) (0, 125, 250, 500, 1000 and 2000 ppm) were tested at two soak times (24 and 48 hours) and one control without any treatment. Germination power, germination time at 25, 50 and 75%, and the germination rate index were evaluated. Germination was considered when the seed emits the hypocotyl outside the substrate used. Chemical scarification with GA3 has a positive influence on seed germination of A. subulata. The highest percentage of germination was obtained with GA3 in concentrations of 250 to 2000 ppm, at 24 and 48 hours of soaking. Germination time was affected by the concentration of GA3, being favored at a concentration of 1000 and 2000 ppm at 24 and 48 hours of soaking; while in other treatments 75% of germination was not reached. Chemical scarification with GA3 favored the germination rate index

Multivector Field Formulation of Hamiltonian Field Theories: Equations and Symmetries

We state the intrinsic form of the Hamiltonian equations of first-order Classical Field theories in three equivalent geometrical ways: using multivector fields, jet fields and connections. Thus, these equations are given in a form similar to that in which the Hamiltonian equations of mechanics are usually given. Then, using multivector fields, we study several aspects of these equations, such as the existence and non-uniqueness of solutions, and the integrability problem. In particular, these problems are analyzed for the case of Hamiltonian systems defined in a submanifold of the multimomentum bundle. Furthermore, the existence of first integrals of these Hamiltonian equations is considered, and the relation between {\sl Cartan-Noether symmetries} and {\sl general symmetries} of the system is discussed. Noether's theorem is also stated in this context, both the ``classical'' version and its generalization to include higher-order Cartan-Noether symmetries. Finally, the equivalence between the Lagrangian and Hamiltonian formalisms is also discussed.Comment: Some minor mistakes are corrected. Bibliography is updated. To be published in J. Phys. A: Mathematical and Genera

Análisis de las roturas del anillo de expansión LD

Presentamos la revisión clínica de 17 casos de roturas del anillo de expansión tipo LD implantados en nuestro Servicio entre 1989 y 1994, de un total de 779 prótesis totales de cadera (2,2%). Se realiza un estudio de las posibles causas que produjeron la rotura del material. Predominaron en pacientes con sobrepeso y con una actividad física intensa. En el análisis de las radiografías destacamos como factores favorecedores de la rotura, la cobertura insuficiente del anillo y su movilización en 16 pacientes (94,1%). Estos hechos obligaron a realizar estudios de elementos finitos y mecánicos que llevaron a la modificación del anillo inicial. El nuevo anillo se ha recubierto de hidroxiapatita y se han trasladado hacia la periferia los orificios para los tornillos. También se ha reducido el espesor y el tamaño de las ranuras entre las aletas.We present the clinical study of 17 breakage of the LD expansive metalling ring, of 779 total hip prosthesis (2,2%) implanted in our Service from 1989 to 1994. An analysis was performed to discover the reasons of the breakage. Dominated in patients with a high activity and overweight. In the roentgenographic analysis of the ring, we emphaise insufficient cover and migration of the ring as predisposing factors in 16 patients (94,1%). For these facts we performed a finite and mechanical element analysis that changed the original ring. The new ring is hyrdoxiapatite coated and the hole for the screws have move periferically. The thickness and the space between slits have been also reduced