Effect of Work of Adhesion on Nanoindentation

Three adhesion contact models, JKR (Johnson-Kendall-Roberts), DMT (Derjaguin-Muller-Toporov) and MD (Maugis-Dugdale) are compared with the Hertz model in dealing with the nano-contact problems. It has been shown that the dimensionless load parameter, $\bar{P}=P/(\pi\Delta\gamma R)$, and the transition parameter, $\Lambda$, have significant influences on the contact stiffness (contact area) at micro/nano-scale and should not be ignored in shallow nanoindentation.

Crack Tip Field and J-Integral with Strain Gradient Effect

The mode I plane strain crack tip field with strain gradient effects is presented in this paper based on a simplified strain gradient theory within the framework proposed by Acharya and Bassani. The theory retains the essential structure of the incremental version of the conventional J_2 deformation theory No higher-order stress is introduced and no extra boundary value conditions beyond the conventional ones are required. The strain gradient effects are considered in the constitutive relation only through the instantaneous tangent modulus. The strain gradient measures are included into the tangent modulus as internal parameters. Therefore the boundary value problem is the same as that in the conventional theory Two typical crack Problems are studied: (a) the crack tip field under the small scale yielding condition induced by a linear elastic mode-I K-field and (b) the complete field for a compact tension specimen. The calculated results clearly show that the stress level near the crack tip with strain gradient effects is considerable higher than that in the classical theory The singularity of the strain field near the crack tip is nearly equal to the square-root singularity and the singularity of the stress field is slightly greater than it. Consequently, the J-integral is no longer path independent and increases monotonically as the radius of the calculated circular contour decreases.

Revelation of a Functional Dependence of the Sum of Two Uniaxial Strengths/Hardness on Elastic Work/Total Work of Indentation

Dimensional and finite element analyses were used to analyze the relationship between the mechanical properties and instrumented indentation response of materials. Results revealed the existence of a functional dependence of (engineering yield strength sigma(E,y) + engineering tensile strength sigma(E,b))/Oliver & Pharr hardness on the ratio of reversible elastic work to total work obtained from an indentation test. The relationship links up the Oliver & Pharr hardness with the material strengths, although the Oliver & Pharr hardness may deviate from the true hardness when sinking in or piling up occurs. The functional relationship can further be used to estimate the SUM sigma(E,y) + sigma(E,b) according to the data of an instrumented indentation test. The sigma(E,y) + sigma(E,b) value better reflects the strength of a material compared to the hardness value alone. The method was shown to be effective when applied to aluminum alloys. The relationship can further be used to estimate the fatigue limits, which are usually obtained from macroscopic fatigue tests in different modes.

Style and the “Idea” of the sophist after Plato : the impact of form typology on sophistic teaching and writing on interdisciplinary scholarly work

Resumen: Después de la primera sofística, los sofistas actuaron entre el resto de los pensadores del Mediterráneo como un grupo definido. Dado que hay muchos ejemplos que muestran que los sofistas ejercían sus prácticas y que también eran personas comprometidas en otras actividades, vamos a examinar aquí diversos casos de semejanzas y diferencias entre ellos y otros grupos de pensadores. Nuestras tres preguntas fundamentales son: qué, cómo y por qué los sofistas escribían y enseñaban. Intentaremos responder haciendo un análisis diacrónico de las principales formas y géneros de escritura que produjeron (qué). El cómo lo responderemos en su desenvolvimiento como una actividad comunicativa más allá de las fronteras de las disciplinas de la época. El por qué tendrá su respuesta al enfatizar la necesidad de la actividad de los sofistas en la socialización de la época y en la educación de la antigüedad. Al aseverar que el estilo era la idea de los sofistas, ponemos la noción de idea en Platón en el contexto de idea derivado de los sofistas contemporáneos a él y de los sofistas posteriores (segunda sofística) y centramos el foco en la función de visualidad expresada en su concepto de idea desde las obras sofísticas más tempranas en la época de Platón hasta las contribuciones posteriores.

La problemática de la traducción en la Carta de Aristeas a Filócrates

Resumen: El trabajo propone una reflexión acerca de la problemática de la traducción en la Antigüedad tal como se plantea en la Carta de Aristeas a Filócrates, narración compuesta en el siglo II a.C. que relata los sucesos en torno a la traducción al griego del Pentateuco, la Septuaginta. El autor, anónimo, narra en primera persona y se describe como integrante de la corte real de Ptolomeo Filadelfo, aunque en realidad se trata de un judío alejandrino, conocedor de las leyes mosaicas. La obra presenta ciertas incongruencias y pasajes de difícil interpretación, pero su mensaje es claro: por medio de la traducción, el original hebreo alcanza la dignidad suficiente como para formar parte de la biblioteca de Alejandría, junto con otras obras prestigiosas del mundo helenístico.

Estudio del comportamiento de plagas y enfermedades en el cultivo de cafe, mediante el uso de recuento integral Masatepe, Masaya

El estudio se realizó en el Centro de Capacitación y Servicio Regional Pacífico (Jardín Botánico) ubicado en la ciudad de Masatepe, Masaya, en el periodo comprendido entre Marzo del 2001 a Febrero del 2002. El objetivo fue evaluar la utilidad del recuento integral de plagas en el fortalecimiento de la toma de decisiones de manejo de plagas y enfermedades, de acuerdo al comportamiento que estas presentan en cada lote. Para la realización del trabajo se tomaron 10 lotes ya establecidos y en plena producción con diferentes manejo, distancias de siembra, niveles de sombra y variedades distintas. La metodología contempló 5 puntos por lote y 1O plantas por punto; tomando a cada una, variables de: número de hojas totales, número de hojas enfermas, número de frutos totales, número de frutos dañados. Las plagas y enfermedades con menor porcentaje de incidencia en general fueron: Minador (Leucoptera co.ffel/a Guerin), Cochinilla (Planoccocus citri L) y Antracnosis (Collectotrichum sp). Las acciones de manejo se establecerían de acuerdo a los niveles presentados, para los cuales se tomo el criterio de 10% para enfermedades foliares; 5% para enfermedades que afectan hojas y frutos; y el 5% para la Broca. Las plagas y enfermedades que se presentaron durante el estudio fueron: Roya, Mancha de Hierro, Antracnosis, Broca, Minador. Considerando a la mancha de Hierro y Broca como las de mayor importancia. El lote Catuai Rojo presentó la mayor incidencia de enfermedades afectado por: Roya (Hemileia Vastatrix, Berk y Br.) y Mancha de hierro (Cercospora co.ffeico/a Berk y cook.), el manejo implementado fue preventivo (podas sanitarias, selectivas y de recepo ). El lote con mayor incidencia de plaga, fue Salchicha Vegetal (SV), la acción de manejo implementadas fueron: la utilización de trampas semioquímicas y endosulfan.

Characterization of the Fracture Work for Ductile Film Undergoing the Micro-Scratch

The interface adhesion strength (or interface toughness) of a thin film/substrate system is often assessed by the micro-scratch test. For a brittle film material, the interface adhesion strength is easily obtained through measuring the scratch driving forces. However, to measure the interface adhesion strength (or interface toughness) for a metal thin film material (the ductile material) by the microscratch test is very difficult, because intense plastic deformation is involved and the problem is a three-dimensional elastic-plastic one. In the present research, using a double-cohesive zone model, the failure characteristics of the thin film/substrate system can be described and further simulated. For a steady-state scratching process, a three-dimensional elastic-plastic finite element method based on the double cohesive zone model is developed and adopted, and the steady-state fracture work of the total system is calculated. The parameter relations between the horizontal driving forces (or energy release rate of the scratching process) and the separation strength of thin film/substrate interface, and the material shear strength, as well as the material parameters are developed. Furthermore, a scratch experiment for the Al/Si film/substrate system is carried out and the failure mechanisms are explored. Finally, the prediction results are applied to a scratch experiment for the Pt/NiO material system given in the literature.

Steady-state crack growth and fracture work based on the theory of mechanism-based strain gradient plasticity

Mode I steady-state crack growth is analyzed under plane strain conditions in small scale yielding. The elastic-plastic solid is characterized by the mechanism-based strain gradient (MSG) plasticity theory [J. Mech. Phys. Solids 47 (1999) 1239, J. Mech. Phys. Solids 48 (2000) 99]. The distributions of the normal separation stress and the effective stress along the plane ahead of the crack tip are computed using a special finite element method based on the steady-state fundamental relations and the MSG flow theory. The results show that during the steady-state crack growth, the normal separation stress on the plane ahead of the crack tip can achieve considerably high value within the MSG strain gradient sensitive zone. The results also show that the crack tip fields are insensitive to the cell size parameter in the MSG theory. Moreover, in the present research, the steady-state fracture toughness is computed by adopting the embedded process zone (EPZ) model. The results display that the steady-state fracture toughness strongly depends on the separation strength parameter of the EPZ model and the length scale parameter in the MSG theory. Furthermore, in order for the results of steady crack growth to be comparable, an approximate relation between the length scale parameters in the MSG theory and in the Fleck-Hutchinson strain gradient plasticity theory is obtained.

Work Softening And Annealing Hardening Of Deformed Nanocrystalline Nickel

We reported that work softening takes place during room-temperature rolling of nanocrystalline Ni at an equivalent strain of around 0.30. The work softening corresponds to a strain-induced phase transformation from a face-centered cubic (fcc) to a body-centered cubic (bcc) lattice. The hardness decreases with increasing volume fraction of the bcc phase. When the deformed samples are annealed at 423 K, a hardening of the samples takes place. This hardening by annealing can be attributed to a variety of factors including the recovery transformation from the bcc to the fcc phase, grain boundary relaxation, and retardation of dislocation gliding by microtwins.

Papel de la mecanización agrícola en el desarrollo integral de la sociedad. Elementos para la planificación de estrategias de mecanización. Un caso de estudio

La mecanización agrícola, como parte integral del desarrollo agropecuario de un país, tiene como fin contribuir a superar el déficit de alimentación, siempre y cuando, planificadores y políticos entiendan la dimensión de ésta como instrumento de desarrollo. Dicha estrategia será positiva si se toma en cuenta elementos primarios de cada región, como son: población, conocimientos, tradiciones culturales, características climáticas, al igual que aspectos que apoyan al desarrollo de los citados elementos, como son: créditos, instalaciones, infraestructuras, etc. La propuesta de mecanización debe involucrar productores, empresarios, industriales, beneficiarios, el gobierno en su papel de rector de las políticas a establecer y las instituciones de investigación, asesoría y prueba, como garantices de definición de los sistemas de producción y tecnología a implementar. Investigación realizada a finales de 1997, con el propósito de conocer el estado de la mecanización en la zona del pacíficcrsur de Nicaragua, indica que el nivel mas común de mecanización utiliza fuente de energía mixta: tracción motriz y animales de tiro. Utilizando fincas de tres extensiones, en presencia de cuatro cultivos, se realizo un análisis de rentabilidad de los tres niveles más utilizados, a partir del cual se propone una estrategia de mecanización.

Experimental Verification And Theoretical Analysis Of The Relationships Between Hardness, Elastic Modulus, And The Work Of Indentation

The relationship between hardness (H), reduced modulus (E-r), unloading work (W-u), and total work (W-t) of indentation is examined in detail experimentally and theoretically. Experimental study verifies the approximate linear relationship. Theoretical analysis confirms it. Furthermore, the solutions to the conical indentation in elastic-perfectly plastic solid, including elastic work (W-e), H, W-t, and W-u are obtained using Johnson's expanding cavity model and Lame solution. Consequently, it is found that the W-e should be distinguished from W-u, rather than their equivalence as suggested in ISO14577, and (H/E-r)/(W-u/W-t) depends mainly on the conical angle, which are also verified with numerical simulations. (C) 2008 American Institute of Physics.

Barium-Functionalized Multiwalled Carbon Nanotube Yarns As Low-Work-Function Thermionic Cathodes

Barium-functionalized multiwalled carbon nanotube yarns were fabricated by drawing and twisting multiwalled carbon nanotube forests through a solution containing barium nitrate. After heat activation under vacuum, the functionalized yarns were enriched in barium oxide due to the high surface-to-volume ratio of the nanotubes. The cathodes exhibited good thermionic properties, with a work function as low as 1.73-2.06 eV and thermionic current density that exceeded 185 mA/cm(2) in a field of 850 V/5 mm at 1317 K. The barium-functionalized yarns had high tensile strength of up to 420 MPa and retained strength of similar to 250 MPa after a 2 h activation process. (C) 2008 American Institute of Physics.

Educación integral de la sexualidad de mujeres y de varones : desafío de nuestra época

La autora expone en el presente artículo algunos conceptos sobre sexualidad y las consideraciones que se deben tener en cuenta a la hora de educar a varones y a mujeres en el tema, teniendo en cuenta sus diferencias y peculiaridades corporales, psicoafectivas, espirituales y sociales. El objetivo para con los jóvenes es brindarles una visión integradora de la sexualidad, integrándola con el amor.

Un testigo directo de las tensiones religiosas en la Alejandría de los siglos IV y V D.C. : Páladas de Alejandría en la Antología Palatina

Abstract: Although he is the most prolific writer of the Greek Anthology, Palladas’ life is almost unknown. But, in spite of the limited biographical data, his work has fortunately been preserved in the GA. Because of his literary creation, the old times rewarded him with the nickname Μετέωρος, high, since the literary merits of a hundred poems of his authorship was recognized (others are discussed by critics). A dozen of them contains invaluable information about the political, religious and social situation in Alexandria immediately after the victory of the bishop Theophilus, Cyril’s predecessor and uncle, during the conflict between Christians and Gentiles, each sector backed up by an Alexandrian population segment (cfr. 9.528, 10.82, 10.85) . Resigned at times, constantly demanding, Palladas complains about the decline of the belief professed by him due to the increasing penetration of the new faith. Therefore, four epigrams record the conversion of the temple of Tyche into a tavern (9.180-183) and 10.90 seems to attack the doctrine of the Resurrection. When religion and politics go hand-in-hand, when religious conspiracies link up with palace intrigues, consequences are predictable: a man called Doroteo denounced him for his negative response to the new dogma, which caused him the loss of his teacher paid work. His annoyance was even greater with further sufferings, chiefly economic, and he had to sell his books (9.171 and 9.175) among other desperate decisions Forewarned about his radical bitterness against Church, it is just to make clear that he is not fully acquiescent with ancient gods and heroes. Thus, in 5.257 he questions Zeus’ ars amandi, in 9.377 refutes Tantalus’ possibility of thirst and hunger in Hades and 9.773 mischievously points out that Eros has been changed into a pan. The work begins with the selection, personal translation and comprehensive analysis of twenty two epigrams. Through such philological aid, we attempt to verify the frictions and the main perceptible factors in his poetic creation to justify his worldview, according to the pagan sentiment widespread in that time before the twilight already overwhelming of its ailing traditions