Evidence for intergranular tunnelling in polyaniline passivated α-Fe nanoparticles

Nanoparticles are of immense importance both from the fundamental and application points of view. They exhibit quantum size effects which are manifested in their improved magnetic and electric properties. Mechanical attrition by high energy ball milling (HEBM) is a top down process for producing fine particles. However, fineness is associated with high surface area and hence is prone to oxidation which has a detrimental effect on the useful properties of these materials. Passivation of nanoparticles is known to inhibit surface oxidation. At the same time, coating polymer film on inorganic materials modifies the surface properties drastically. In this work a modified set-up consisting of an RF plasma polymerization technique is employed to coat a thin layer of a polymer film on Fe nanoparticles produced by HEBM. Ball-milled particles having different particle size ranges are coated with polyaniline. Their electrical properties are investigated by measuring the dc conductivity in the temperature range 10–300 K. The low temperature dc conductivity (I–V ) exhibited nonlinearity. This nonlinearity observed is explained on the basis of the critical path model. There is clear-cut evidence for the occurrence of intergranular tunnelling. The results are presented here in this paper

Thread Scheduling Mechanisms for Multiple-Context Parallel Processors

Scheduling tasks to efficiently use the available processor resources is crucial to minimizing the runtime of applications on shared-memory parallel processors. One factor that contributes to poor processor utilization is the idle time caused by long latency operations, such as remote memory references or processor synchronization operations. One way of tolerating this latency is to use a processor with multiple hardware contexts that can rapidly switch to executing another thread of computation whenever a long latency operation occurs, thus increasing processor utilization by overlapping computation with communication. Although multiple contexts are effective for tolerating latency, this effectiveness can be limited by memory and network bandwidth, by cache interference effects among the multiple contexts, and by critical tasks sharing processor resources with less critical tasks. This thesis presents techniques that increase the effectiveness of multiple contexts by intelligently scheduling threads to make more efficient use of processor pipeline, bandwidth, and cache resources. This thesis proposes thread prioritization as a fundamental mechanism for directing the thread schedule on a multiple-context processor. A priority is assigned to each thread either statically or dynamically and is used by the thread scheduler to decide which threads to load in the contexts, and to decide which context to switch to on a context switch. We develop a multiple-context model that integrates both cache and network effects, and shows how thread prioritization can both maintain high processor utilization, and limit increases in critical path runtime caused by multithreading. The model also shows that in order to be effective in bandwidth limited applications, thread prioritization must be extended to prioritize memory requests. We show how simple hardware can prioritize the running of threads in the multiple contexts, and the issuing of requests to both the local memory and the network. Simulation experiments show how thread prioritization is used in a variety of applications. Thread prioritization can improve the performance of synchronization primitives by minimizing the number of processor cycles wasted in spinning and devoting more cycles to critical threads. Thread prioritization can be used in combination with other techniques to improve cache performance and minimize cache interference between different working sets in the cache. For applications that are critical path limited, thread prioritization can improve performance by allowing processor resources to be devoted preferentially to critical threads. These experimental results show that thread prioritization is a mechanism that can be used to implement a wide range of scheduling policies.

On-the-Fly Maintenance of Series-Parallel Relationships in Fork-Join Multithreaded Programs

A key capability of data-race detectors is to determine whether one thread executes logically in parallel with another or whether the threads must operate in series. This paper provides two algorithms, one serial and one parallel, to maintain series-parallel (SP) relationships "on the fly" for fork-join multithreaded programs. The serial SP-order algorithm runs in O(1) amortized time per operation. In contrast, the previously best algorithm requires a time per operation that is proportional to Tarjan’s functional inverse of Ackermann’s function. SP-order employs an order-maintenance data structure that allows us to implement a more efficient "English-Hebrew" labeling scheme than was used in earlier race detectors, which immediately yields an improved determinacy-race detector. In particular, any fork-join program running in T₁ time on a single processor can be checked on the fly for determinacy races in O(T₁) time. Corresponding improved bounds can also be obtained for more sophisticated data-race detectors, for example, those that use locks. By combining SP-order with Feng and Leiserson’s serial SP-bags algorithm, we obtain a parallel SP-maintenance algorithm, called SP-hybrid. Suppose that a fork-join program has n threads, T₁ work, and a critical-path length of T[subscript ∞]. When executed on P processors, we prove that SP-hybrid runs in O((T₁/P + PT[subscript ∞]) lg n) expected time. To understand this bound, consider that the original program obtains linear speed-up over a 1-processor execution when P = O(T₁/T[subscript ∞]). In contrast, SP-hybrid obtains linear speed-up when P = O(√T₁/T[subscript ∞]), but the work is increased by a factor of O(lg n).

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Project management exercises

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Mejoramiento Productivo "Apparel Basic Ltda"

Para el presente trabajo realizado en la Universidad del Rosario, buscamos hacer un mejoramiento productivo de la empresa Apparel Basic Ltda. Teniendo en cuenta todas las herramientas aprehendidas durante la academia y aplicando esto a una empresa del sector real de confecciones. Se centrara el análisis principalmente en las tres áreas donde se observan los mayores problemas organizacionales: Producción, manejo de inventarios y entrega de producto. En el primer análisis se realizara todo el estudio del proceso de producción, teniendo en cuenta la distribución en planta, las rutas críticas de proceso, los diagramas de flujo de producto, el análisis de las principales referencias, entre otros. Todo esto con el fin de identificar los principales errores y poder proponer herramientas y procesos de mejora que sean de ayuda para esta organización. El siguiente análisis se desarrollara en el manejo de inventarios; dentro de este aspecto se analizaran la distribución de las bodegas de producto, la identificación de los productos de mayor rotación, el planteamiento de indicadores de gestión, entre otros procesos, con el fin de identificar procesos benéficos para la empresa que aceleren y mejoren el flujo de producto al interior de la organización. Luego de esto, se analiza todo el proceso de alistamiento y entrega de producto ya que es uno de los principales problemas dentro de la organización porque se esta incumpliendo con los pedidos de los clientes lo que genera un problema de insatisfacción por parte de los clientes.

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Análisis de la influencia del fenómeno del ciberterrorismo en las dinámicas de seguridad de la Unión Europea

El fenómeno del ciberterrorismo se constituye como una nueva amenaza a la seguridad internacional, este fenómeno es el resultado de distintos procesos en el sistema internacional como el de la globalización. La definición del concepto se establece por la convergencia entre el ciberespacio y el terrorismo. El objetivo de esta investigación es explicar las distintas dimensiones del ciberterrorismo, métodos de ataque, acciones pasadas, propósito del fenómeno, situación actual y vulnerabilidades. El objeto de estudio de esta investigación es la Unión Europea como actor del sistema internacional que se ha visto afectado por este fenómeno. También se dará uso al aparato teórico de los complejos de seguridad desarrollado por Barry Buzan para evidenciar las nuevas amenazas del sistema internacional y analizar los procesos de securitización del fenómeno en el seno de la Unión Europea.