6,889 research outputs found
Stress effects on the kinetics of hydrogen adsorption in a spherical particle: An analytical model
No full textWe consider a two-phase elastic solid subject to diffusion-induced phase transformation by interstitial hydrogen. We derive a simple analytical model to quantify the effect of misfit strain on the kinetic of phase transformation and to calculate the amplitude of the well-know hysteresis cycle observed when a sequence of forward and reverse phase transformations takes place. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved
On the Effect of Elastic Distortions on the Kinetics of Diffusion-Induced Phase Transformations
No full textWe derive the evolution equation for a sharp concentric interface in a two-phase elastic solid of spherical shape. The solid is immersed in a reservoir of interstitial species whose diffusion triggers phase transformation. We find that mismatch strain accelerates phase–transformation processes that initiate at the center of the specimen, and slows down those that begin at the boundary
Musculoskeletal loading database: loading conditions of the proximal femur
No full textKnowledge of musculoskeletal loading conditions in humans is mandatory for the design of endoprosthestic and osteosynthetic devices. Also, new treatment options such as tissue generation and transplantation require knowledge of the mechanical loads under which tissue formation and regeneration takes place. In this manuscript, a database on musculo-skeletal loading of the proximal femur is presented. The data are based on individual patient gait and radiological data. By means of inverse dynamics and optimization techniques, the internal loads acting at the joint and within the muscles have been determined. The calculated hip contact force has been validated by means of in vivo measurements in four patients. The database is freely available and gives an estimate on internal loads acting at the proximal femur for activities like walking and stair climbing
Determination of muscle loading at the hip joint for use in pre-clinical testing
No full textThe stability of joint endoprostheses depends on the loading conditions to which the implant-bone complex is exposed. Due to a lack of appropriate muscle force data, less complex loading conditions tend to be considered in vitro. The goal of this study was to develop a load profile that better simulates the in vivo loading conditions of a "typical" total hip replacement patient and considers the interdependence of muscle and joint forces. The development of the load profile was based on a computer model of the lower extremities that has been validated against in vivo data. This model was simplified by grouping functionally similar hip muscles. Muscle and joint contact forces were computed for an average data set of up to four patients throughout walking and stair climbing. The calculated hip contact forces were compared to the average of the in vivo measured forces. The final derived load profile included the forces of up to four muscles at the instances of maximum in vivo hip joint loading during both walking and stair climbing. The hip contact forces differed by less than 10% from the peak in vivo value for a "typical" patient. The derived load profile presented here is the first that is based on validated musculoskeletal analyses and seems achievable in an in vitro test set-up. It should therefore form the basis for further standardisation of pre-clinical testing by providing a more realistic approximation of physiological loading conditions
Land and changing social relations in South Africa's former reserves : the case of Luphaphasi in Sakhisizwe Local Municipality, Eastern Cape.
No full textIncludes abstract.
Includes bibliographical references
Reflexiones sobre la duda metódica fingida
No full textReflexiones acerca de la duda metódica fingida. Esto es lo que hace el matemático cuando quiere recordar los pasos que conducen a la demostración de un teorema, o el físico y el químico, cuando procura a sus alumnos la adquisición de una verdad de orden experimental. Es la duda que usan los escolásticos, cuando al comienzo de sus cuestiones se preguntan, por ejemplo, utrum Deus existat; no dudan ciertamente que existe Dios, pero por razones científicas prescinden de sus certidumbres para mostrar el proceso que explícita y ordenadamente lleva a la verdad desde sus cimientos lógicos
Liquid helium flows around an oscillating cylinder
No full textThe complementary flows of normal viscous liquid helium (He I) and of superfluid helium (He II) around an oscillating obstacle, of rectangular cross-section, have been studied experimentally by using the particle tracking velocimetry technique, with solid deuterium particles. The observed particle behaviour in He II is very similar to that seen in He I. It seems therefore that, without some kind of special forcing acting differently on each superfluid helium component, on length scales which the experiment can access, the oscillating quantum flow mimics the classical one
Alterações na fertilidade de um latossolo devido à prática da calagem recomendada pelo método de incubação.
No full textCom objetivo de quantificar as alterações no pH e nos teores de Ca, Mg e AI trocaveis em urn Latossolo devido a calagem, coletados em Serra do Mel-RN, utilizou-se cinco doses de calcario comercial com as seguintes caractensticas: CaO (32,7%); MgO (7,4%); poder de neutralização (76,7%); reatividade (99,2%) e poder relativo de neutralização total (76,1 %). Estimou-se a necessidade de calagem e em função do teor de Al trocavel e utilizou-se 5 nfveis de calagem correspondentes a 0, 0,5,1,0,1,5 e 2,0 vezes adose maxima recomendada para as respectivas profundidades que equivalem as quantidades de calcario aplicadas. Amostras con tendo 200 g de solo foram acondicionadas em sacos plasticos, onde 0 calcario foi adicionado e homogeneizado. Ap6s cada perfodo de incubação (0, 7,14,21,28 e 35 dias), foram feitas leituras de pH as quais foram relacionadas com as doses de calcario adicionadas, para obtenção da curva de incubação. Ao final do experimento, detenninou-se os teores de AP+, Ca2+e Mg2+com objetivo de avaliar a capacidade do corretivo no fomecimento desses nutrientes. Os tratamentos foram arranjados seguindo urn fatorial completo (2x5x7) e dispostos em delineamento inteiramente casualizado com tres repetições. Os fatores testados foram: profundidade do solo, doses de calcario e tempo de incubação. Os dados obtidos foram submetidos a analise de variancia e de regressao para cad a uma das variaveis de res posta. Diante dos resultados obtidos pode-se concluir que 0 calcario comercial utilizado pode ser utilizado como corretivo de acidez de solos; a quantidade de calcfuio a aplicar deve ser calculada utilizando-se 0 metodo de incubação para evitar sub ou superestimativa de dosagem, e necessario urn perfodo rnfnimo de 35 dias de incubação
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