Energetics and structural properties of twist grain boundaries in Cu

Structural and energetics properties of atoms near a grain boundary are of great importance from theoretical and experimental standpoints. From various experimental work it is concluded that diffusion at low temperatures at polycrystalline materials take place near grain boundary. Experimental and theoretical results also indicate changes of up to 70 percent in physical properties near a grain boundary. The Embedded Atom Method (EAM) calculations on structural properties of Au twist grain boundaries are in quite good agreement with their experimental counterparts. The EAM is believed to predict reliable values for the single vacancy formation energy as well as migration energy. However, it is not clear whether the EAM functions which are fitted to the bulk properties of a perfect crystalline solid can produce reliable results on grain boundaries. One of the objectives of this work is to construct the EAM functions for Cu and use them in conjunction with the molecular static simulation to study structures and energetics of atoms near twist grain boundaries in Cu. This provides tests of the EAM functions near a grain boundary. In particular, we determine structure, single vacancy formation energy, migration energy, single vacancy activation energy, and interlayer spacing as a function of distance from grain boundary. Our results are compared with the available experimental and theoretical results from grain boundaries and bulk

Square-Root Finding Problem In Graphs, A Complete Dichotomy Theorem

Graph G is the square of graph H if two vertices x,y have an edge in G if and only if x,y are of distance at most two in H. Given H it is easy to compute its square H^2. Determining if a given graph G is the square of some graph is not easy in general. Motwani and Sudan proved that it is NP-complete to determine if a given graph G is the square of some graph. The graph introduced in their reduction is a graph that contains many triangles and is relatively dense. Farzad et al. proved the NP-completeness for finding a square root for girth 4 while they gave a polynomial time algorithm for computing a square root of girth at least six. Adamaszek and Adamaszek proved that if a graph has a square root of girth six then this square root is unique up to isomorphism. In this paper we consider the characterization and recognition problem of graphs that are square of graphs of girth at least five. We introduce a family of graphs with exponentially many non-isomorphic square roots, and as the main result of this paper we prove that the square root finding problem is NP-complete for square roots of girth five. This proof is providing the complete dichotomy theorem for square root problem in terms of the girth of the square roots

Diffusion on Cu surfaces

Understanding surface diffusion is essential in understanding surface phenomena, such as crystal growth, thin film growth, corrosion, physisorption, and chemisorption. Because of its importance, various experimental and theoretical efforts have been directed to understand this phenomena. The Field Ion Microscope (FIM) has been the major experimental tool for studying surface diffusion. FIM have been employed by various research groups to study surface diffusion of adatoms. Because of limitations of the FIM, such studies are only limited to a few surfaces: nickel, platinum, aluminum, iridium, tungsten, and rhodium. From the theoretical standpoint, various atomistic simulations are performed to study surface diffusion. In most of these calculations the Embedded Atom Method (EAM) along with the molecular static (MS) simulation are utilized. The EAM is a semi-empirical approach for modeling the interatomic interactions. The MS simulation is a technique for minimizing the total energy of a system of particles with respect to the positions of its particles. One of the objectives of this work is to develop the EAM functions for Cu and use them in conjunction with the molecular static (MS) simulation to study diffusion of a Cu atom on a perfect as well as stepped Cu(100) surfaces. This will provide a test of the validity of the EAM functions on Cu(100) surface and near the stepped environments. In particular, we construct a terrace-ledge-kink (TLK) model and calculate the migration energies of an atom on a terrace, near a ledge site, near a kink site, and going over a descending step. We have also calculated formation energies of an atom on the bare surface, a vacancy in the surface, a stepped surface, and a stepped-kink surface. Our results are compared with the available experimental and theoretical results

Improving corrosion performance by surface patterning

In this research, the effect of surface patterning on the corrosion behaviour of a metal (nickel) was investigated. The idea originates from the fact that hydrophobic (low or non wettable) surfaces can decrease the contact area between a corrosive solution and a surface. In the current work, special surface patterns were created on pure nickel sheets. The corrosion behaviour of those surfaces was studied using a dynamic polarization method in 0.5M H2SO4. It was found that there is a trend or dependency between the hole size (D), the hole distance (L), and the corrosion current density (lcorr). The higher the (D/L)2 ratio, the higher the corrosion current density (lcorr). The corrosion potential (Ecorr) of all samples was lower than that of the reference sample in all the tests. SEM images showed that after the first corrosion test some local corroded regions were created on the surfaces but in the samples with the lowest lcorr there was a slight change in the surface

RIBBONS: Rapid Inpainting Based on Browsing of Neighborhood Statistics

Image inpainting refers to filling missing places in images using neighboring pixels. It also has many applications in different tasks of image processing. Most of these applications enhance the image quality by significant unwanted changes or even elimination of some existing pixels. These changes require considerable computational complexities which in turn results in remarkable processing time. In this paper we propose a fast inpainting algorithm called RIBBONS based on selection of patches around each missing pixel. This would accelerate the execution speed and the capability of online frame inpainting in video. The applied cost-function is a combination of statistical and spatial features in all neighboring pixels. We evaluate some candidate patches using the proposed cost function and minimize it to achieve the final patch. Experimental results show the higher speed of 'Ribbons' in comparison with previous methods while being comparable in terms of PSNR and SSIM for the images in MISC dataset

Image Inpainting by Hyperbolic Selection of Pixels for Two Dimensional Bicubic Interpolations

Image inpainting is a restoration process which has numerous applications. Restoring of scanned old images with scratches, or removing objects in images are some of inpainting applications. Different approaches have been used for implementation of inpainting algorithms. Interpolation approaches only consider one direction for this purpose. In this paper we present a new perspective to image inpainting. We consider multiple directions and apply both one-dimensional and two-dimensional bicubic interpolations. Neighboring pixels are selected in a hyperbolic formation to better preserve corner pixels. We compare our work with recent inpainting approaches to show our superior results

El papel de la enseñanza de matemáticas basada en problemas de acuerdo con el modelo de Kirkpatrick sobre el desempeño de resolución de problemas de los profesores de matemáticas

The process of evaluation is essentially the process of determining the realization of the educational goals in real terms through curriculum and education and represents the changes that occur in human behavior. Therefore, it is necessary that at the end of each training course (such as training classes, workshops, and training seminars), the teacher or evaluators, evaluate the implemented training program. In the curriculum approaches, learning the problem-solving ability is the ultimate goal of mathematics education. This skill requires empowering teachers with problem solving skills as one of the optimal ways to use capacities and to achieve educational goals. Therefore, the main goal of this study was to examine the problem-based mathematics teaching according to the Krikpatrick's model on problem-solving performance of mathematics teachers. The research design was of a pretest-posttest type with a control group. Using simple random sampling method, 100 male and female mathematics teachers, teaching mathematics at the middle school, were selected from Rabat Karim city, Tehran province. In pre-test and post-test of the traditional teaching and problem-solving based teaching in mathematics, data were collected through mathematical problem-solving performance test and Kirkpatrick's four-level questionnaire. Using SPSS software and R software, the results showed a significant difference between the scores of problem-solving performances between the two groups of control and experiment after the training, and through the equations, we showed that each level of the Kirkpatrick's model has a positive effect on the post-test scores of mathematics teachers.El proceso de evaluación es esencialmente el proceso de determinar la realización de los objetivos educativos en términos reales a través del currículo y la educación, y representa los cambios que ocurren en el comportamiento humano. Por lo tanto, es necesario que al final de cada curso de capacitación (como clases de capacitación, talleres y seminarios de capacitación), el maestro o evaluadores evalúen el programa de capacitación implementado. En los enfoques curriculares, aprender la capacidad de resolución de problemas es el objetivo final de la educación matemática. Esta habilidad requiere empoderar a los maestros con habilidades de resolución de problemas como una de las formas óptimas para usar las capacidades y alcanzar metas educativas. Por lo tanto, el objetivo principal de este estudio fue examinar la enseñanza de las matemáticas basada en problemas de acuerdo con el modelo de Krikpatrick sobre el rendimiento en la resolución de problemas de los profesores de matemáticas. El diseño de la investigación fue de un tipo de prueba previa y posterior con un grupo de control. Usando un método de muestreo aleatorio simple, se seleccionaron 100 maestros de matemáticas masculinos y femeninos, que enseñan matemáticas en la escuela secundaria, de la ciudad de Rabat Karim, provincia de Teherán. En las pruebas previas y posteriores de la enseñanza tradicional basada en la enseñanza de la resolución de problemas en matemáticas, los datos se recopilaron mediante la prueba de rendimiento de la resolución de problemas matemáticos y el cuestionario de cuatro niveles de Kirkpatrick. Usando el software SPSS y el software R, los resultados mostraron una diferencia significativa entre los puntajes de desempeño de resolución de problemas entre los dos grupos de control y experimento después del entrenamiento, y a través de las ecuaciones, demostramos que cada nivel del modelo de Kirkpatrick tiene un efecto positivo en las puntuaciones posteriores a la prueba de los profesores de matemáticas

Square Root Finding In Graphs

Abstract: Root and root finding are concepts familiar to most branches of mathematics. In graph theory, H is a square root of G and G is the square of H if two vertices x,y have an edge in G if and only if x,y are of distance at most two in H. Graph square is a basic operation with a number of results about its properties in the literature. We study the characterization and recognition problems of graph powers. There are algorithmic and computational approaches to answer the decision problem of whether a given graph is a certain power of any graph. There are polynomial time algorithms to solve this problem for square of graphs with girth at least six while the NP-completeness is proven for square of graphs with girth at most four. The girth-parameterized problem of root fining has been open in the case of square of graphs with girth five. We settle the conjecture that recognition of square of graphs with girth 5 is NP-complete. This result is providing the complete dichotomy theorem for square root finding problem

Essays in Corporate Prediction Markets

Personal subjective opinions are one of the most important assets in management. Prediction markets are mechanisms that can be deployed to elicit and aggregate a group of people’s opinions regarding the outcome of future events at any point in time. Prediction markets are exchange-traded markets where security values are tied to the outcome of future events. Prediction markets are systematically designed in a way that their market prices capture the crowd’s consensus about the probability of a future event. Corporations harness internal prediction markets for managerial decision making and business forecasting. Prediction markets are traditionally designed for large and diverse populations, two properties that are not often displayed in corporate settings. Therefore special considerations must be given to prediction markets used in corporations. Our first contribution in this thesis is in addressing the issue of diversity, in the sense of risk preferences, in corporate prediction markets. We study prediction markets in the presence of risk averse or risk seeking agents that have unknown risk preferences. We show that such agents’ behavior is not desirable for the purpose of information aggregation. We then characterize the agents’ behavior with respect to prediction market parameters and offer a systematic method to market organizers that fine tunes market parameters so at to best mitigate the impact of a pool agents’ risk-preferences. Our Second contribution in this thesis is in recommending prediction market mechanisms in different settings. There are many prediction market mechanisms with various advantages and weaknesses. The choice of a market mechanism can heavily affect the market accuracy and in turn, the success of a managerial decision, or a forecast based on prediction markets’ prices. Using trade data from two real-world prediction markets, we study the two main types of prediction markets mechanism and provide the much-needed insight as to what market mechanism to choose in various situations