191 research outputs found
Effects de l'anisotropie solide-solide sur les microstructures de solidification directionnelle
No full textThe microstructures arising from the solidification processing possess various types of boundaries: solid(S)-liquid(L) interfaces, grain boundaries (GB), interphase boundaries (IB). Whereas solid-liquid interface has been investigated extensively, relatively little attention has been paid to the S-S boundaries (GB and IB). Recently, it has been found that S-S boundary anisotropy can also have a significant influence, particularly on the overall orientation selection of the growing patterns. The present thesis investigates the effects of GB and IB anisotropy through simulations of solidification morphologies. We use a recent multi-phase field model for this study. In essence, we work with a grand-canonical functional combining the interfacial and bulk free energies of the system and then minimising it with respect to the field variables to obtain the equations of motion for the phase fields and the composition fields. We use this code to study three problems stemming from the directional solidification of lamellar eutectics and polycrystals with a particular focus on the effects of the solid-solid boundary anisotropy. During thin-film directional solidification experiments on lamellar eutectics, it has been observed that in response to the IB anisotropy, lamellae grow at an angle with the growth axis. We characterize this drift angle using our numerical simulations and then compare it successfully with a recent theoretical prediction. Then, we exploit this IB anisotropy in bulk lamellar eutectics to understand the emergence of certain minimum energy directions in the system leading to preferred orientations in the microstructure. Then, we repeat our thin-film eutectic study for polycrystals with grain boundaries, motivated by the fact that anisotropic low-angle grain boundaries or sub-boundaries grow at an angle with respect to the growth axis. We quantify this tilt angle and compare it successfully with a recent analytical prediction. In this way, we establish the influence of the solid-solid boundary anisotropy on the directionally solidified microstructures.Les microstructures qui se forment lors de la solidification d'alliagescontiennent différent types d'interfaces: des interfaces solide-liquid (SL),des joints de grain (grain boundaries, GB) et des joints interphase(interphase boundaries, IB). Tandis que les interfaces solide-liquideont beaucoup été étudiés, les interfaces solide-solide (GB et IB) ontreçu peu d'attention. Récemment, il a été démontré que l'anisotropie deces interfaces solide-solide peut aussi avoir une influence marquée, enparticulier sur la texture et les orientations des motifs sélectionnés.Dans cette thèse, la relation entre anisotropie solide-solide et sélectionmorphologique est étudiée à l'aide de simulations numériques de microstructuresde solidification.Nous utilisons un modèle multi-champ-de-phase récemment développé. Cemodèle est basé sur une fonctionnelle grand-canonique qui combine lesénergies libres de volume et de surface. Sa minimisation donne leséquations de mouvement pour les champs de phase et de concentration.Ce code est utilisé pour examiner trois problèmes qui viennent dela solidification directionnelle d'alliages eutectiques et dilués,avec une attention particulière aux effets de l'anisotropiedes interfaces solide-solide.Durant la solidification d'alliages eutectiques en échantillons minces,il a été observé qu'en réponse à l'anisotropie des IB, les lamelleseutectiques croissent dans une direction qui fait un angle bien définiavec la direction de croissance principale. Nous caractérisons cetangle dans nos simulations numériques, et trouvons un bon accord avecune théorie récente de la croissance anisotrope. Ensuite, nous examinonsle lien entre l'anisotropie des IB et l'émergence d'orientations préférentiellesdans des systèmes étendus. Finalement, nous répétons notre étude d'échantillonsminces pour des polycristaux, dans lesquels des GB de faible désorientationcroissent également avec un angle défini par rapport à la direction principalede croissance. Nous déterminons cet angles de croissance et trouvons à nouveauun bon accord avec des prédictions théoriques. De cette manière, nous confirmonsl'influence de l'anisotropie solide-solide sur les microstructures desolidification directionnelle
Effects de l'anisotropie solide-solide sur les microstructures de solidification directionnelle
No full textThe microstructures arising from the solidification processing possess various types of boundaries: solid(S)-liquid(L) interfaces, grain boundaries (GB), interphase boundaries (IB). Whereas solid-liquid interface has been investigated extensively, relatively little attention has been paid to the S-S boundaries (GB and IB). Recently, it has been found that S-S boundary anisotropy can also have a significant influence, particularly on the overall orientation selection of the growing patterns. The present thesis investigates the effects of GB and IB anisotropy through simulations of solidification morphologies. We use a recent multi-phase field model for this study. In essence, we work with a grand-canonical functional combining the interfacial and bulk free energies of the system and then minimising it with respect to the field variables to obtain the equations of motion for the phase fields and the composition fields. We use this code to study three problems stemming from the directional solidification of lamellar eutectics and polycrystals with a particular focus on the effects of the solid-solid boundary anisotropy. During thin-film directional solidification experiments on lamellar eutectics, it has been observed that in response to the IB anisotropy, lamellae grow at an angle with the growth axis. We characterize this drift angle using our numerical simulations and then compare it successfully with a recent theoretical prediction. Then, we exploit this IB anisotropy in bulk lamellar eutectics to understand the emergence of certain minimum energy directions in the system leading to preferred orientations in the microstructure. Then, we repeat our thin-film eutectic study for polycrystals with grain boundaries, motivated by the fact that anisotropic low-angle grain boundaries or sub-boundaries grow at an angle with respect to the growth axis. We quantify this tilt angle and compare it successfully with a recent analytical prediction. In this way, we establish the influence of the solid-solid boundary anisotropy on the directionally solidified microstructures.Les microstructures qui se forment lors de la solidification d'alliagescontiennent différent types d'interfaces: des interfaces solide-liquid (SL),des joints de grain (grain boundaries, GB) et des joints interphase(interphase boundaries, IB). Tandis que les interfaces solide-liquideont beaucoup été étudiés, les interfaces solide-solide (GB et IB) ontreçu peu d'attention. Récemment, il a été démontré que l'anisotropie deces interfaces solide-solide peut aussi avoir une influence marquée, enparticulier sur la texture et les orientations des motifs sélectionnés.Dans cette thèse, la relation entre anisotropie solide-solide et sélectionmorphologique est étudiée à l'aide de simulations numériques de microstructuresde solidification.Nous utilisons un modèle multi-champ-de-phase récemment développé. Cemodèle est basé sur une fonctionnelle grand-canonique qui combine lesénergies libres de volume et de surface. Sa minimisation donne leséquations de mouvement pour les champs de phase et de concentration.Ce code est utilisé pour examiner trois problèmes qui viennent dela solidification directionnelle d'alliages eutectiques et dilués,avec une attention particulière aux effets de l'anisotropiedes interfaces solide-solide.Durant la solidification d'alliages eutectiques en échantillons minces,il a été observé qu'en réponse à l'anisotropie des IB, les lamelleseutectiques croissent dans une direction qui fait un angle bien définiavec la direction de croissance principale. Nous caractérisons cetangle dans nos simulations numériques, et trouvons un bon accord avecune théorie récente de la croissance anisotrope. Ensuite, nous examinonsle lien entre l'anisotropie des IB et l'émergence d'orientations préférentiellesdans des systèmes étendus. Finalement, nous répétons notre étude d'échantillonsminces pour des polycristaux, dans lesquels des GB de faible désorientationcroissent également avec un angle défini par rapport à la direction principalede croissance. Nous déterminons cet angles de croissance et trouvons à nouveauun bon accord avec des prédictions théoriques. De cette manière, nous confirmonsl'influence de l'anisotropie solide-solide sur les microstructures desolidification directionnelle
Mejorando el rendimiento de RPL utilizando Redes definidas por Software
No full textABSTRACT: Wireless Sensor Networks (WSNs) are special networks used in the Internet of Things (IoT) scheme, in which nodes are constrained by many parameters such as memory or energy. Therefore, the routing protocol used in these networks needs to be specially adapted for such constraints. Usually, the routing topology in these networks is created and maintained by the nodes in a distributed fashion due scalability reasons. Thus, the nodes only have a limited local view of the network. The routing protocol must also feature capabilities of auto-repair, allowing nodes to use alternative routes when link failures occur, or if other links are better, and rebuilding the network when too many of these failures have taken place. The Routing Protocol for Low power and Lossy Networks (RPL) possesses these characteristics and is used this thesis.
The aim of the thesis is to develop a new solution with a centralized global view of the network that is less constrained than the limited local view of the distributed topology, since it gives the opportunity to have other aspects into account when creating the topology or rebuilding the network. Therefore, the state information about the topology that the nodes have, instead of computing it locally by them, will be computed and pushed to the nodes by this centralized view, creating a Software De_ned Network (SDN).
Thus, the tasks of the thesis comprises:
Task (i): Understand the state of the art of the protocol and decide which features of the protocol are needed for an RPL solution.
Task (ii): Determine how the centralized view can be used to improve the RPL protocol, designing a proper SDN solution.
Task (iii): Develop an implementation, in a network simulator, of the features needed from the protocol, adding also the features of the new SDN solution.
Task (iv): Evaluate and compare the performance of the new SDN solution with the standard RPL solution, based on the previous implementation. This evaluation includes parameters such as the control packets overhead or the percentage of time that the packet losses.RESUMEN: Las Wireless Sensor Networks (WSN), son unas redes especiales, que se usan en el esquema del Internet of Things (IoT), en las que los nodos tienen limitaciones en muchos de sus parámetros como pueden ser la memoria o energía. Por lo tanto, el protocolo de enrutamiento utilizado en estas redes, tiene que estar especialmente adaptado para estas limitaciones. Normalmente, la topología de red en este tipo de redes es creada y mantenida por los nodos de manera distribuida, debido a razones de escalabilidad.
En consecuencia, los nodos tienen una visión limitada de la red. El protocolo de enrutamiento además debe ofrecer capacidades de auto reparación, permitiendo a los nodos utilizar rutas alternativas cuando haya fallos en sus enlaces, o si unos enlaces son mejores que otros, y reconstruyendo la red cuando muchos de estos fallos hayan tenido lugar. El protocolo de enrutamiento RPL posee estas características y es usado en esta tesis.
El objetivo de la tesis es desarrollar una nueva solución que tenga una visión global de la red, que no sea tan limitada como la visión local que tienen los nodos en el caso de que la topología sea distribuida, dado que deja tener otros aspectos en cuenta a la hora de crear la topología o reconstruir la red. En consecuencia, la información que los nodos deben guardar sobre la topología, en lugar de ser calculada por ellos, deberá ser calculada y enviada a los nodos por esta visión global, creando una Software Defined Network (SDN).
Por lo tanto, las tareas de esta tesis comprenden:
Tarea (i): Entender el estado del arte del protocolo y decidir cuáles son las características del mismo que se necesitan para una solución RPL.
Tarea (ii): Determinar cómo esta visión global puede ser usada para mejorar el protocolo RPL, planteando una adecuada solución SDN.
Tarea (iii): Desarrollar una implementación, en un simulador de red, de las características necesarias del protocolo, agregando también las características de la nueva solución SDN.
Tarea (iv): Evaluar y comparar el rendimiento de la nueva solución SDN con la solución RPL estándar. Esta evaluación incluye parámetros como el número de paquetes de control o las pérdidas de paquetes.Ingeniería en Informátic
Combining ability analysis for yield and yield components in bold grained rice (Oryza sativa L.) of Assam
No full textCombining ability analysis for grain yield and its components was carried out in eight parental diallel crosses of bold grained rice excluding reciprocals. The general combining ability (GCA) and specific combining ability (SCA) effects were significant for all the characters indicating the importance of both additive and non-additive gene effects in their inheritance. The parents Ranjit followed by Matonga and Monohar Sali contributed significantly to high GCA effect towards high grain yield per hill. The superior specific cross combinations for high grain yield per hill were Matonga/Bar Madhava, originated from high x low GCA combination followed by Dhola Mula/ Ranjit (low x high gca), Chandmoni/Hathi Sali (low x high GCA), Dhola Mula/Mala (low x low gca), Matonga/Mala (high x low GCA), Bar Madhava/Hathi Sali (low x high GCA) and Matonga/Hathi Sali (high x high GCA). Further, these crosses exhibited high SCA effects for some other characters as well
India's education challenges: Expenditure Effectiveness Issues
No full textHuman capital investments through education are widely recognized as being important for economic growth. This phenomenon has led governments in many developing countries to make significant investments in the education sector. Despite this, public expenditure in education remains low in countries such as India, the country which accounts for the largest number of children aged below 15 years. Estimates from the World Bank show that over the last two decades, total public expenditure on education has stagnated in India, and remains below 4 per cent of gross domestic product (GDP). This figure has only increased marginally from 2.8 per cent in 1997 to 3 per cent in 2010, and has declined as percentage of total government expenditure from 12.5 per cent in 1998 to 10.5 per cent in 2010 (World Bank, 2012). The Indian economy has experienced high levels of economic growth over this period, with the average rate of annual GDP growth in the decade to 2010 slightly above 7 per cent, compared to an annual rate of 4.5 per cent in the previous four decades 1960–2000 (Cagliarini and Baker, 2010). Evidence from Alkire and Santos’ (2010) recently developed Multidimensional Poverty Index (MPI) shows that India performs poorly for the education indicators in comparison to other countries where data are available. For example, India is ranked 68th out of 104 countries with data for the indicator ‘years of schooling’ (which measures if no household member has completed five years of schooling) and is ranked 57th out of 85 countries with data for school enrolment (measured as a schoolaged child being out of school in years 1–8). Indeed on July 2013, the Supreme Court of India provided a damning indictment of the education system in India by stating that although literacy rates had increased over the years, the education system in the country has failed to achieve its objective and that it has to be reformed immediately (NDTV, 2013).</p
Decentralization, indirect tax reform and fiscal federalism in India
No full textIt is a time honoured cliche that India is a country of immense diversity. In operational terms, a well-established and functioning federalism is a dire necessity for effective governance of the country. A fundamental requirement for this is the establishment of a relationship of trust between all principal stakeholders in India's federal set-up: the central government, states, regions and even villages and panchayats. This involves inter alia that all stakeholders be clear about their responsibilities and rights and that financial flows between these stakeholders are predictable and easily understood. This, of course, does not imply a financial straitjacket but the clear enunciation of rules and circumstances under which departures from the established norms would be undertaken. Such arrangements would require constant review, updating and recalibration of the entire gamut (and not piecemeal) of federal relations - tax, expenditure and transfers. This is particularly important at this time since there is widespread agreement that states have become the new engines of economic growth in India whence inter-state and centre-state financial relations should remain positioned on an even keel to ensure high economic growth and the consequent poverty reduction
Fiscal implications of food security in India: a critical review
No full textThis book seeks to balance normative prescriptions on fiscal policy with its practical aspects in the context of the Indian scenario. In doing so, it brings together views of leading experts from academic and policy spheres. It highlights the specificities of Indian fiscal policy and studies current issues like the impact of development expenditures, the Goods and Services Tax (GST), the challenge of reducing subsidies and different aspects of political economy. India's Fiscal Policy discusses rapid developments in the field following the fiscal stimulus of 2008, subsequent attempts at fiscal consolidation and the formation of the NDA government. It focuses on policy and political considerations and adopts a wider approach for the analysis of fiscal policy by taking into consideration aspects such as the effectiveness and targeting of social expenditures, which are essential for a critical analysis of the Indian policy matrix. Provides non-jargonistic explanation of basic concepts Highlights practical aspects, political economy issues and specificities of Indian fiscal policy not covered by conventional 'text book' approaches Includes supplementary material for students of economics for public finance or macroeconomics course
Electronic Transport in Nanotransistors.
No full textIn this work we will make use of techniques developed in the fundamentals of nanoelectronics, to address a new approach to conductance in circuits without nanoscale. When we go to nanoscales, we must make some modifications in the physics that we know, requiring a transition from classical physics to quantum physics. In this work we will present the properties of electron conduction in nanotransistors and the origins of quantum resistance, and consequently we compared some pre-stipulated concepts with new concepts. Most of this work is based on books published by the physicist Supriyo Datta, who is the pioneer in this study.Neste trabalho faremos uso de técnicas desenvolvidas nos fundamentos da nanoeletrônica, para tratar de uma nova abordagem da condutância nos circuitos em nanoescala. Quando partimos para nanoescalas, devemos fazer algumas modificações na física que conhecemos, exigindo uma transição da física clássica para a física quântica.Também apresentaremos as propriedades da condução eletrônica em nanotransistores e as origens da resistência quântica. Por consequência vamos comparar alguns conceitos pré estipulados com novos conceitos. A maior parte deste trabalho é embasada nos livros publicados pelo físico Supriyo Datta, que é o pioneiro nesse estudo.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq
Investigation of a ceramic metal matrix composite functional surface layer manufactured using gas tungsten arc welding
No full textWear resistant surfaces with high toughness and impact resistant properties are
to be created to improve the life cycle cost of brake discs for trains. A potential
solution to this industrial problem is to use an arc cladding process. This work
describes the application of gas tungsten arc welding (GTAW) for a structural
ceramic Metal Matrix Composite (MMC) on steel. The structure of the two
ceramics examined indicates the possibility of development of a wear resistant
surface, which would extend the life of the brake disc. Silicon Carbide (SiC)
and Tungsten Carbide (WC) ceramics were studied to embed them in a steel
matrix by an advanced GTAW method. WC particles penetrated the liquid weld
pool and also partially dissolved in the steel matrix, whereas, SiC because of
the physical properties never penetrated deeper into the weld pool but
segregated on the surface. Successful embedding and bonding of WC led to
the decision to exercise an in-depth analysis of the bonding between the WC
particles and the matrix. Chemical analysis of the matrix revealed more WC
dissolution as compared to particle form within the clad. It was observed that
WC reinforcement particles built a strong chemical bond with the steel matrix.
This was shown by electron backscatter diffraction (EBSD) analysis. The hard
clad layer composed of WC reinforced steel matrix gave an matching friction
coefficient to high-strength steel in cold wear conditions through Pin-on-Disc
wear and friction testing. A prototype railway brake disc was created with the
established GTAW parameters to find out the difficulties of producing industrial
scale components
Zero field spin splitting in indium gallium arsenide/indium aluminum arsenide heterostructures
No full textThe InGaAs/InAlAs heterojunction is a promising material system for high speed device applications and opto-electronic integration. From beating effects observed in Shubnikov-de Haas (SdH) oscillations it is demonstrated that the degeneracy of the conduction band is lifted in zero magnetic field in this material system. The SdH oscillations observed in two pseudomorphic samples and one lattice matched sample show clear beats with up to six null points for magnetic fields B less than 1T. This field is low enough that the effect of non-parabolicity is deemed insignificant. Zero field spin splittings of 1.5-2.75meV were obtained for the three samples. Two mechanisms produce zero field spin splitting in semiconductor heterostructures: (i) a k-cube term arising from crystal inversion asymmetry and (ii) the Rashba term due to interface-spin-orbit-interaction. It is demonstrated that in this material system only one of these mechanisms is dominant and that it is probably the Rashba term. From investigation of the spin splitting in a tilted magnetic field, negative g-factors for 2-3 are obtained for these materials
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