Non-proper helicoid-like limits of closed minimal surfaces in 3-manifolds

We show that there exists a metric with positive scalar curvature on S2xS1 and a sequence of embedded minimal cylinders that converges to a minimal lamination that, in a neighborhood of a strictly stable 2-sphere, is smooth except at two helicoid-like singularities on the 2-sphere. The construction is inspired by a recent example by D. Hoffman and B. White.Comment: 12 pages, 3 figures, replaced because of corrupted fil

argumentación escrita en ingenieria

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Laboratory Characterization of Ohio Gold Frac Sand

The mechanical response of sand depends on state variables (such as density, stress state and fabric) and intrinsic variables (such as particle size distribution and particle shape). The mechanical response of sand is also a function of sand crushability. Recent research studying the cone penetration process in a unique digital image correlation (DIC) chamber is underway at Purdue University. The test sand is Ohio Gold Frac sand, which meets criteria regarding particle size and gradation related to elimination of chamber boundary and scale effects. The mechanical behavior of this sand can be simulated by a suitable constitutive model, such as the Purdue Sand Model (PSM). In order to calibrate the constitutive model, a number of laboratory tests are required. This thesis describes some of these tests, which include determination of index properties, particle mineralogy and morphology, one-dimensional compression tests, direct shear and ring shear tests. Ohio Gold Frac sand is classified as a clean, poorly-graded silica sand (99% of silica content). Additionally, the minimum and maximum void ratios are equal to 0.59 and 0.81, respectively. The critical-state direct shear friction angle is 35°, while the critical-state ring shear friction angle is 31.3°. Particle crushing was observed in one-dimensional compression tests, ring shear tests as well as in cone penetration tests. In order to understand the degree of particle crushing and the process by which it happens, the evolution of particle gradation and morphology of Ohio Gold Frac sand was assessed both before and after one-dimensional compression and ring shear tests. One-dimensional compression tests were performed to a maximum load of 74 kN (24 MPa); the onset of crushing for loose and dense samples of Ohio Gold Frac sand occurred at normal stresses of 9 MPa and 10 MPa, respectively. Ring shear tests were performed on Ohio Gold Frac sand with normal stresses of 100 kPa, 200 kPa, 300 kPa and 400 kPa and shear displacements ranging from 1 to 20 m. Cycles of compression and dilation followed by stages of stabilization due to particle crushing were observed in all the tests. The results indicated that particle damage within the shear band (with a thickness of about 6 mm) increased with increasing normal stresses and shear displacements. The fines content of the sand in the shear band increased to 5% after the ring shear test performed with a normal stress of 400 kPa and 7 m of shear displacement. The main particle damage mechanisms that affected the gradation of Ohio Gold Frac sand after loading were abrasion and shearing off of asperities of large particles and splitting of the small particles, which produced an increment of the fines content of the sand, without affecting the maximum particle size

MAC Protocols Used by Wireless Sensor Networks and a General Method of Performance Evaluation

Many researchers employ IEEE802.15.4 as communication technology for wireless sensor networks (WSNs). However, medium access control (MAC) layer requirements for communications in wireless sensor networks (WSNs) vary because the network is usually optimized for specific applications. Thus, one particular standard will hardly be suitable for every possible application. Two general categories of MAC techniques exist: contention based and schedule based. This paper explains these two main approaches and includes examples of each one. The paper concludes with a unique performance analysis and comparison of benefits and limitations of each protocol with respect to WSNs

Estereotipos de hombre que manejan las revistas colombianas Soho y Vea

La presente investigación se refiere al tema de los estereotipos de hombre que manejan las revistas SOHO y VEA en sus ediciones especiales del mes de septiembre de 2016, la característica principal de estas ediciones es que son para el público femenino, dando una introducción a los hombres en el mensaje publicitario, la investigación de este fenómeno social se realizó por el interés de conocer cómo han evolucionado los estereotipos de belleza masculina en el país y cuánto ha proliferado. En el marco de la teoría sociológica, la investigación se realizó con una serie de análisis a las revistas antes mencionadas, para lograr esto tenemos como objetivos; Objetivo general: Analizar el estereotipo de hombre que maneja las revistas Soho y Vea en sus ediciones especiales del mes de septiembre del 2016. Lo que lleva a la necesidad de cumplir con los siguientes objetivos específicos. Reconocer los estereotipos de hombres manejados por las revistas, Estudiar los conceptos presentes en la imagen masculina que manejan las revistas, Establecer una comparación del concepto de hombre antes y después de su transformación en las revistas y Analizar los cambios del hombre mediatizado a través de los últimos años

Los estilos parentales en la etapa de la adolescencia

33 Páginas.Los estilos educativos parentales ejercen gran influencia durante el desarrollo infantil que se reflejarán más adelante en el adolescente. Dada la importancia de los cambios durante la adolescencia, inicialmente se revisaran los diferentes estilos parentales que se han planteado en psicología y algunas investigaciones relacionadas con esto. Se ha hecho también una revisión de los estilos de crianza durante la época de la adolescencia en investigaciones recientes y la relación que existe entre los estilos de padres y los problemas que se presentan durante la adolescencia, bien sean internalizantes o externalizantes. Por último, se expondrán las conclusiones con referencia a la revisión realizada