Analysis of the Results of Surface Free Energy Measurement of Ti6Al4V by Different Methods

AbstractSurface Free Energy (SFE) of solids should be calculated using theoretical models. The contact angle (CA) measurement on a surface is considered the most practical way to obtain the SFE. The results of five methods based in the models are compared: the method of Zisman (ZI), the geometric mean (GM), the harmonic mean (HM), the Lifshitz-van der Waals/ Acid-Base (LW/AB) and the equation of state (ES). The SFE calculated with GM, HM and LW/AB methods change with the amount and type of liquid used, however, when water, glycerol and dimethyl sulfoxide are used together the SFE and its dispersive and polar components are similar in value for the three methods. In the case of the ES model the values of SFE change with the liquid used; finally using the ZI method the SFE values are 20% lower than the values of SFE obtained with the other methods

Polynomial functions for direct calculation of the surface free energy developed from the Neumann Equation of State method

The Neumann Equation of State (EQS) allows obtaining the value of the surface free energy of a solid {\gamma}_{SV} from the contact angle ({\theta}) of a probe liquid with known surface tension {\gamma}_{LV}. The value of {\gamma}_{SV} is obtained by numerical methods solving the corresponding EQS. In this work, we analyzed the discrepancies between the values of {\gamma}_SV obtained using the three versions of the EQS reported in the literature. The condition number of the different EQS was used to analyze their sensitivity to the uncertainty in the {\theta} values. Polynomials fit to one of these versions of EQS are proposed to obtain values of {\gamma}_{SV} directly from contact angles ({\gamma}_SV ({\theta})) of particular probe liquids. Finally, a general adjusted polynomial is presented to obtain the values of {\gamma}_{SV} not restricted to a particular probe liquid ({\gamma}_{SV}({\theta},{\gamma}_{LV})). Results showed that the three versions of EQS present non-negligible discrepancies, especially at high values of {\theta}. The sensitivity of the EQS to the uncertainty in the values of {\theta} is very similar in the three versions and depends on the probe liquid used (greater sensitivity at higher {\gamma}_{LV}) and on the value of {\gamma}_{SV} of the solid (greater sensitivity at lower {\gamma}_{SV}). The discrepancy of the values obtained by numerical resolution of both the fifth-order fit polynomials and the general fit polynomial was low, no larger than {\pm}0.40 mJ/m^{2}. The polynomials obtained allow the analysis and propagation of the uncertainty of the input variables in the determination of {\gamma}_{SV} in a simple and fast way.Comment: 37 pages, 13 figure

Análisis de la resistencia de una microestructura de solidificación dendrítica equiaxial

En piezas metálicas obtenidas por solidificación se distingue la estructura en granos equiaxiales o columnares y a nivel microscópico cada grano presenta una estructura dendrítica que es determinantes en las propiedades del producto final. En el presente trabajo se desarrolla un modelo de elementos finitos bidimensional para estudiar los efectos del tamaño de la dendrita, la curvatura de la punta y la orientación respecto a la carga sobre los campos de tensión y deformación de una microestructura de solidificación dendrítica. Se construyen microestructuras artificiales que constan de una matriz homogénea con una sola dendrita equiaxial mediante una curva polar que indica las direcciones de crecimiento dendrítico, se simula un ensayo de tracción simple en régimen elastoplástico considerando dos fases que poseen igual rigidez pero distintas propiedades plásticas e interactuando mediante una adherencia perfecta. Se analizó diferentes condiciones de contorno para simular un ensayo mecánico mediante deformación controlada en un análisis de elementos finitos y se dedujo la respuesta mecánica del material mixto a partir de la heterogeneidad de los campos tensión – deformación. Se encontró, para una misma relación de fases, una dependencia entre la distribución de tensiones y su valor medio según la forma y la orientación de la dendrita, lo cual incide en la resistencia de la microestructura.Publicado en: Mecánica Computacional vol. XXXV no.33Facultad de Ingenierí

Modelado de la influencia de la microestructura en la microdureza de materiales con recubrimiento

Mediante simulación numérica se estudió la microdureza en un material metálico recubierto con óxido metálico. La simulación consiste de un contacto bidimensional axisimétrico entre un indentador esférico y un sistema sustrato-recubrimiento. Se consideró un sustrato formado por titanio recubierto con otro material más duro a diferentes cargas de indentación y espesores del recubrimiento, considerando dos casos: ambos materiales perfectamente adheridos o los dos materiales interactuando a través de una interfaz cohesiva. Se analizaron los efectos de las propiedades mecánicas de cada material sobre el comportamiento global del sistema, la relacion entre dureza y espesor del recubrimiento, la influencia de fallas locales en la interfaz y de la estructura de granos en sustrato y recubrimiento. Los resultados permitieron obtener correlaciones entre la dureza y las propiedades mecánicas y geométricas del sistema. Se destaca que cuando el recubrimiento es delgado es posible explicar la dispersión en resultados de microdureza en un material recubierto si se tienen en cuanta fallas de adhesión en la interfaz y la estructura de granos en el sustrato.Publicado en: Mecánica Computacional vol. XXXV no.36Facultad de Ingenierí

Photography-based taxonomy is inadequate, unnecessary, and potentially harmful for biological sciences

The question whether taxonomic descriptions naming new animal species without type specimen(s) deposited in collections should be accepted for publication by scientific journals and allowed by the Code has already been discussed in Zootaxa (Dubois & Nemésio 2007; Donegan 2008, 2009; Nemésio 2009a–b; Dubois 2009; Gentile & Snell 2009; Minelli 2009; Cianferoni & Bartolozzi 2016; Amorim et al. 2016). This question was again raised in a letter supported by 35 signatories published in the journal Nature (Pape et al. 2016) on 15 September 2016. On 25 September 2016, the following rebuttal (strictly limited to 300 words as per the editorial rules of Nature) was submitted to Nature, which on 18 October 2016 refused to publish it. As we think this problem is a very important one for zoological taxonomy, this text is published here exactly as submitted to Nature, followed by the list of the 493 taxonomists and collection-based researchers who signed it in the short time span from 20 September to 6 October 2016

Inverse relationship between cerebrovascular lesions and severity of lewy body pathology in patients with lewy body diseases

Cerebrovascular pathology is a major cause of stroke and mortality. Studies on prevalence of cerebrovascular pathologies in dementia with Lewy bodies (DLBs) and Parkinson disease (PD) patients are scarce and contradictory. We aimed to determine the prevalence and severity of cerebrovascular pathologies in DLB and PD and to analyze their relationship to LB pathology. The prevalence and severity of atherosclerosis in the circle of Willis, cerebral amyloid angiopathy, cerebral infarcts, hemorrhages, small-vessel disease, white matter lesions, including the Consortium to Establish a Registry for Alzheimer Disease (CERAD) protocol as well as Braak neurofibrillary tangle stages for AD pathology were analyzed in autopsy-verified DLB (n = 13), PD (n = 102), and control subjects (n = 53). In all patient groups, the extent of LB pathology was inversely correlated to the severity of most vascular pathologies (atherosclerosis, infarcts, and small-vessel disease; all p < 0.05). By contrast, cerebral amyloid angiopathy, CERAD, and Braak neurofibrillary tangle stages were positively correlated with LB pathology (p < 0.05). Whereas the overall prevalence and severity of small-vessel disease, infarcts, hemorrhages, and white matter lesions were comparable among both disease groups, the extents of atherosclerosis, cerebral amyloid angiopathy, CERAD, and Braak neurofibrillary tangle stages were significantly higher in DLB than in those of PD patients (p < 0.05). Microinfarcts were statistically more prevalent in each patient group than in controls, whereas gross infarcts predominated in controls (p < 0.05 each). In conclusion, DLB and PD patients with advanced LB pathology were less likely to show severe cerebrovascular disease or history of stroke. © 2010 by the American Association of Neuropathologists, Inc

Modeling Alveolar Soft Part Sarcomagenesis in the Mouse: A Role for Lactate in the Tumor Microenvironment

SummaryAlveolar soft part sarcoma (ASPS), a deadly soft tissue malignancy with a predilection for adolescents and young adults, associates consistently with t(X;17) translocations that generate the fusion gene ASPSCR1-TFE3. We proved the oncogenic capacity of this fusion gene by driving sarcomagenesis in mice from conditional ASPSCR1-TFE3 expression. The completely penetrant tumors were indistinguishable from human ASPS by histology and gene expression. They formed preferentially in the anatomic environment highest in lactate, the cranial vault, expressed high levels of lactate importers, harbored abundant mitochondria, metabolized lactate as a metabolic substrate, and responded to the administration of exogenous lactate with tumor cell proliferation and angiogenesis. These data demonstrate lactate’s role as a driver of alveolar soft part sarcomagenesis

YPR139c/LOA1 encodes a novel lysophosphatidic acid acyltransferase associated with lipid droplets and involved in TAG homeostasis

LOA1, a yeast member of the glycerolipid acyltransferase family, encodes a novel lysophosphatidic acid acyltransferase associated with lipid droplets (LDs) and involved in triacylglycerol (TAG) accumulation. Loa1p, recruited during LD formation, preferentially directs oleic acid–containing phosphatidic acid species into the TAG biosynthetic pathway