3,381 research outputs found
Strain mapping and nanocrystallite size determination by neutron diffraction in an aluminum alloy (AA5083) severely plastically deformed through equal channel angular pressing
Six specimens of an aluminum alloy (AA-5083) extruded by Equal Channel Angular Pressing following two different routes plus a blank sample were examined with a neutron radiation of 1.5448 Å. Macrostrain maps from the (311) reflection were obtained. A clear difference about accumulated macrostrain with the extrusion cycles between the two routes is shown. The diffraction data of annealed specimens did permit to estimate crystallite sizes that range between 89 nm and 115 nm depending on the routes
Evaluation of the changes in working limits in an automobile assembly line using simulation
The aim of the work presented in this paper consists of the development of a decision-making support system, based on discrete-event simulation models, of an automobile assembly line which was implemented within an Arena simulation environment and focused at a very specific class of production lines with a four closed-loop network configuration. This layout system reflects one of the most common configurations of automobile assembly and preassembly lines formed by conveyors. The sum of the number of pallets on the intermediate buffers, remains constant, except for the fourth closed-loop, which depends on the four-door car ratio (x) implemented between the door disassembly and assembly stations of the car body. Some governing equations of the four closed-loops are not compatible with the capacities of several intermediate buffers for certain values of variable x. This incompatibility shows how the assembly line cannot operate in practice for x0,97 in a stationary regime, due to the starvation phenomenon or the failure of supply to the machines on the production line. We have evaluated the impact of the pallet numbers circulating on the first closed-loop on the performance of the production line, translated into the number of cars produced/hour, in order to improve the availability of the entire manufacturing system for any value of x. Until the present date, these facts have not been presented in specialized literature. © 2012 American Institute of Physics
Ac magnetic susceptibility of a molecular magnet submonolayer directly patterned onto a microSQUID sensor
We report the controlled integration, via Dip Pen Nanolithography, of
monolayer dots of ferritin-based CoO nanoparticles (12 Bohr magnetons) into the
most sensitive areas of a microSQUID sensor. The nearly optimum flux coupling
between these nanomagnets and the microSQUID improves the achievable
sensitivity by a factor 100, enabling us to measure the linear susceptibility
of the molecular array down to very low temperatures (13 mK). This method opens
the possibility of applying ac susceptibility experiments to characterize
two-dimensional arrays of single molecule magnets within a wide range of
temperatures and frequencies.Comment: 4 pages 3 figure
Upper Bound Analysis of the ECAE Process by Considering Strain Hardening Materials and Three-Dimensional Rectangular Dies
Equal channel angular extrusion (ECAE
Fracturas de Astrágalo: EvaluaciĂłn ClĂnico-QuirĂşrgica
Se han revisado 13 pacientes diagnosticados de fractura de astrágalo recogidos
en nuestro Servicio de Urgencias y tratados quirĂşrgicamente en todos los casos. De ellos
se ha realizado un seguimiento clĂnico y radiolĂłgico. En el 46% de los casos se obtuvieron
resultados satisfactorios (23% excelentes y 23% buenos). Los restantes se repartieron entre regulares
(38%) y malos (16%). La necrosis avascular apareció en 3 de los 13 casos, discutiéndose
el origen de esta seria complicaciĂłn.
Siguiendo la clasificación de WEBER, los tipos de fractura más frecuentes fueron el tipo III
(38%) y el II (31%). La congruencia articular postquirúrgica del astrágalo fracturado y el tiempo
de demora en la cirugĂa que debe ser de urgencia, se muestran como factores a considerar en
la evoluciĂłn ulterior del "Aviators astragalus". Se discute asĂ mismo el valor del signo de
Hawkins.Areview of 13 patients diagnosed of Talus fracture has been colected
in our service of trauma emergency. All of them have been managed by surgical
methods and clinical and radiologically followed up. Satisfactory results wer e
obtained in 46% of the cases (23%, excellents and 23%, good results). The rest wer e
regular (38%) and bad (16%). Avascular necrosis was observed in 3 of the 13 cases,
discussing the origin of this serious complication. The most frequent types of
fracture were type III (38%) ant type II (31%) following Weber's classification. The
postsurgical articular congruency of the fractured talus and the delayed time on the
surgery which must be an emergency, seem to be factors to conside r in the later
evolution of the "aviators astragalus". The value of Hawkins sign is also discussed
Comportamiento del polietileno en un simulador de cadera
Se presentan los resultados del comportamiento friccional de cinco diferentes
combinaciones de cabezas protésicas femorales y polietileno acetabular, investigadas
en un simulador de cadera. Las cabezas femorales de aleaciones de Cr-Co-Mo, Cr-Co-Mo
con implantación iónica y de cerámica de zirconia, se articularon con cotilos de polietileno
de ultra-alto-peso molecular y se sometieron a tres millones de ciclos de marcha cada
uno, utilizando un simulador de cadera de cinco estaciones. El desgaste de los cotilos protésicos,
evaluado por mediciones gravimétricas demostró que cuando el espesor de polietileno
era de 10,9 mm el desgaste producido por cabezas de Cr-Co-Mo de 28 mm era de
0,14 mm/año y de 0,09 mm/año si la cabeza utilizada era de 28 mm de aleación de Cr-Co-
Mo con implantación iónica. Cuando el espesor del acetábulo era de 7 mm el desgaste ocasionado
por cabezas de cerámica de zirconia de 28 mm fue de 0,04 mm/año; sin embargo
si tenĂa espesor 10,9 mm y las cabezas de cerámica de zirconia eran de 28 y 32 mm, no aparecĂa
desgaste alguno. Estos resultados indican que el diámetro de la cabeza de cerámica
de 28 y 32 mm, parece no tener importancia alguna, pero sĂ la tiene el que el espesor del
acetábulo protésico sea menor de 10 mm.Ultra high molecular weight polyethylene (UHMWPE) metal backed acetabular
cups were articulated against Cr-Co-Mo alloy, ion implanted Cr-Co-Mo and zirconia
ceramic femoral heads in a five station hip joint simulator, running three tests of three millions
walking cycles with each one of the five different head-cup combinations. The wear
rate of the acetabular cups was measured gravimetrically. When the thickness of the cup
was 10.9 mm, the mean wear rate against 28 mm diameter Cr-Co-Mo femoral heads was
0.14 mm/year, and 0.09 mm/year 'when the cup was articulated against 28 mm ion implanted
Cr-Co-Mo femoral heads. When the thickness of the cup was 7 mm the mean wear rate
was 0.04 mm/year against 28 mm zirconia heads. The results indicate that significant reduction
in the wear of the UHMWPE cup can be achieved when zirconia femoral head is
used and that the diameter of the zirconia femoral head, 28 vs 32 mm, seems unimportant
as wear factor. A cup thickness below 10 mm may result disadvantageous
Revisión de las aplicaciones de la electroerosión por penetración al mecanizado de cerámicas conductoras
Análisis de la influencia de las condiciones de proceso sobre el acabado superficial de materiales cerámicos fabricados por electroerosión
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