La estructura y propiedades magnéticos de las nanopartículas de Fe50Ni50 obtenidas mediante el método de explosión eléctrica de hilo

[Es]Actualmente ninguna área científica es ajena a la revolución de la nanociencia; las nanopartículas atraen el interés de muchos investigadores desde el punto de vista de la ciencia fundamental y para sus aplicaciones tecnológicas. Las nanopartículas ofrecen la posibilidad de fabricar sensores que sean capaces de detectar desde un virus hasta concentraciones de substancias patógenas que no pueden ser detectadas por los métodos convencionales. Hoy en día existes 82 tratamientos contra el cáncer basadas en la utilización de nanopartículas y los materiales composite con nanopartículas se utilizan como medio de protección frente la radiación del rango de microondas. En la rama de ciencias ambientales, las nanopartículas metálicas sirven como materiales anticontaminantes. En este trabajo se ha estudiado la estructura y las propiedades magnéticas de las nanopartículas de FeNi preparadas mediante el método de explosión eléctrica de hilo. Con la técnica de Rayos–X(DRX) se ha determinado que las nanopartículas se cristalizan en un sistema cúbico FCC con un parámetro de celda de 3.596 Å, también, se ha obtenido el tamaño de dominio coherente que es de 35 nm. La muestra se ha sometido a un programa de temperatura controlada para seguir la evolución de la estructura cristalina y del tamaño del cristal, tanto en atmósfera oxidante como en vacío. Para el aprendizaje de los microscopios utilizados en este trabajo, se ha asistido al curso “Fundamentos de microscopia electrónica de barrido y microanálisis” impartido por SGIker de la UPV/EHU. Se han empleado los microscopios electrónicos SEM y TEM para obtener imágenes de gran resolución de la muestra y analizar su contenido elemental. Partiendo de las imágenes sacadas por el SEM se ha calculado el valor medio del tamaño de las partículas de la muestra, 58 nm. Mediante el Mastersizer 2000 se ha medido el tamaño de las partículas y/o agregados por método de difracción láser, disgregando la muestra todo lo posible hasta conseguir el tamaño medio que se aproxime al de una sola partícula, 100nm. Por último, para la caracterización magnética se ha servido del VSM que mide el momento magnético de una muestra cuando ésta vibra en presencia de un campo magnético estático, consiguiendo una imanación de saturación de 125 emu/g. Hemos fabricado y caracterizado las nanopartículas magnéticas de hierro-níquel y los resultados obtenidos han sido enviados a un congreso especializado de ciencia de materiales (ISMANAM - 2013, Italia).

低渗油田“层内爆炸”增产技术的小尺度模拟实验研究

本文是关于低渗油田增产技术的室内模拟实验研究的论文。我们对井内爆炸采油、核爆采油和高能气体压裂进行全面调研以后，吸取了井内爆炸采油的教训，借鉴了高能气体压裂的成功经验，提出了低渗油田“层内爆炸”增产技术。该技术是利用水力压裂技术的现有设备，将适当的炸药压入岩石裂缝，再用适当的方法起爆，从而在岩石裂缝周围产生大量裂缝，在不会对储层产生不利影响也不会毁坏井筒的前提下，达到提高采取收率并增产油气的目的。首先，建立了圆管点火实验装置、小尺度模拟实验装置和平板点火实验装置；然后利用实验装置进行了“层内爆炸”用特种火药和特种炸药配方的探索。通过实验我们至少找到了一种“层内爆炸”用药品的配方，并且在小尺度模拟实验装置中实现了“层内爆炸”基本过程的模拟实验，从而证实“层内爆炸”思路正确，原理上可行。接着，建立了爆燃推进的模型，并在恒稳推进和不可压缩简化条件下得到几组算例，这些解在物理上是合理的。通过计算我们得知爆燃恒温推进的条件是苛刻的，需要多个参数的匹配。通过本人硕士论文的工作，证实了低渗油田“层内爆炸”增产技术在原理上的可行性。但因为“层内爆炸”过程中牵涉到多个特征尺度，因此并不能从小尺度向大尺度简单地推广，下一步工作是建立中大尺度模拟实验装置，考察在中大尺度条件下“层内爆炸”的可行性，为现场实际应用作充分的实验准备。

激光聚焦爆炸耦合场的理论建模与跨尺度计算

针对激光聚焦爆炸的电磁-热力耦合效应,在宏观尺度上,把描述激光电磁波散射和传播的Maxwell方程和高温高压气动流场的Euler方程结合起米,利用热力学状态方程(EOS)和电离平衡方程(Saha方程)并通过理论建模和数值仿真,研究和揭示激光聚焦爆炸效应及激光支持吸收波(LSC/LSD)的产生和演化、以及相关的反冲压力和动量耦合等相互作用机制.

装药弹体侵彻混凝土厚靶中的炸药摩擦起爆模型

基于炸药的热爆炸理论,采用炸药的热点温度(也称为临界起爆温度)作为起爆判据,分析了装药弹体在侵彻混凝土厚靶过程中的炸药安全性问题,建立了炸药摩擦起爆的热传导模型.对模型进行了量纲一化分析,得出量纲一热流率幅值Qm与炸药和弹壳界面量纲一温度峰值T′max的关系,以及可在实际工程中应用的临界量纲一控制参数Qmc,同时得到了反映摩擦产生的热量在炸药与弹壳间分配比例关系的量纲一参数ΚⅠ.结果表明,炸药装药和弹壳接触面间的强摩擦是形成热点、从而导致炸药早炸的一个重要因素.

Numerical and Experimental Investigation On The Prevention of Co Deflagration

The exhaust gases from industrial furnaces contain a huge amount of heat and chemical enthalpy. However, it is hard to recover this energy since exhaust gases invariably contain combustible components such as carbon monoxide (CC). If the CO is unexpectedly ignited during the heat recovery process, deflagration or even detonation could occur, with serious consequences such as complete destruction of the equipment. In order to safely utilize the heat energy contained in exhaust gas, danger of its explosion must be fully avoided. The mechanism of gas deflagration and its prevention must therefore be studied. In this paper, we describe a numerical and experimental investigation of the deflagration process in a semi-opened tube. The results show that, upon ignition, a low-pressure wave initially spreads within the tube and then deflagration begins. For the purpose of preventing deflagration, an appropriate amount of nitrogen was injected into the tube at a fixed position. Both simulation and experimental results have shown that the injection of inert gas can successfully interrupt the deflagration process. The peak value of the deflagration pressure can thereby be reduced by around 50%. (C) 2008 Elsevier Ltd. All rights reserved.

Water quality strategy for the Lockwoods Folly River: A partnership for an ailing river

As with a majority of the remaining undeveloped coastal areas in North Carolina, Brunswick County is not a hidden treasure any more. Since 1980 the county’s population has more than tripled to over 95,000 and another 30,000 or so residents are expected to make this last bastion of undeveloped southeastern NC their home by 2020, even with the current economic downturn. As the 29th fastest growing county in the nation this population explosion is resulting in rapid landscape scale land use changes within the watershed of the Lockwoods Folly River. Subdivisions, shopping centers, new highways and bridges, golf courses, and marinas are becoming significant land use activities. The surging development within this 150-square mile 88 thousand-acre watershed has had a severe effect on the health of the river. The portion of the river closed to shell fishing has more that tripled from 18 percent in 1980 to more than 55 percent today and 60% of the beds are considered impaired. For generations, locals have enjoyed the bounty of the Lockwoods Folly River and estuarine system famed for its rich and abundant shell fish beds and excellent coastal inshore fishing. This river system stretches from the Lockwoods Folly Inlet at the Atlantic Ocean inland where it makes the transformation from saltwater marshes to a winding blackwater river that snakes into hundreds of smaller tributaries and blackwater swamps. (PDF contains 4 pages)

Studies of ion energy and yield from argon clusters heated by intense femtosecond laser pulses

Using time-of-flight spectrometry, the interaction of intense femtosecond laser pulses with argon clusters has been studied by measuring the energy and yield of emitted ions. With two different supersonic nozzles, the dependence of average ion energy (E) over bar on cluster size (n) over bar in a large range of (n) over bar approximate to 3 x 10(3) similar to 3 x 10(6) has been measured. The experimental results indicate that when the cluster size (n) over bar <= 3 x 10(5), the average ion energy (E) over bar proportional to (n) over bar (0.5), Coulomb explosion is the dominant expansion mechanism. Beyond this size, the average ion energy gets saturated gradually, the clusters exhibit a mixed Coulomb-hydrodynamic expansion behavior. We also find that with the increasing gas backing pressure, there is a maximum ion yield, the ion yield decreases as the gas backing pressure is further increased.

飞秒激光在石英玻璃中诱导微爆炸的理论研究

利用有限元方法建立了二维模型，研究了飞秒激光作用下石英玻璃中导带电子的产生、激光能量的沉积、导带电子和能量扩散等微观过程．计算了导带电子扩散引起的局部净电荷及其形成的静电场分布，初步揭示了微爆炸的演化过程．

飞秒强激光场中大尺寸氩团簇爆炸机理的实验研究

By using time-of-flight spectroscopy, the ionization and explosion of large argon clusters ( (n) over bar = 3 x 10(3) - 3 x 10(6)) in the intense femtosecond pulsed laser field (60 fs,2 x 10(16) W/cm(2)) has been studied, and the dependence of average energy of ions emitted from argon clusters on the gas backing pressure has been measured. By comparing the average ion energies obtained with two different supersonic conical nozzles and considering the Hagena's scaling law of clusters, we have found that the average ion energy is determined by the cluster size when the laser parameters are kept unchanged. The experimental results indicated that when the cluster size is less than 3 x 10(5) atoms per cluster, the Coulomb repulsion force is the dominating factor in the expansion mechanism. Beyond this size, for 3 x 10(5) < (n) over barn < 3 x 10(6), the expansion is the result of the combined effect of both the Coulomb repulsion force and the hydrodynamic force, and the latter will play the dominating role for increasing cluster size.

Femtosecond pulse laser-induced self-organized nanostructures on the surface of ZnO crystal

This paper reports self-organized nanostructures observed on the surface of ZnO crystal after irradiation by a focused beam of a femtosecond Ti:sapphire laser with a repetition rate of 250 kHz. For a linearly polarized femtosecond laser, the periodic nanograting structure on the ablation crater surface was promoted. The period of self-organization structures is about 180 nm. The grating orientation is adjusted by the laser polarization direction. A long range Bragg-like grating is formed by moving the sample at a speed of 10 mu m/s. For a circularly polarized laser beam, uniform spherical nanoparticles were formed as a result of Coulomb explosion during the interaction of near-infrared laser with ZnO crystal.

Coulomb expansion of deuterated methane clusters irradiated by an ultrashort intense laser pulse

The simulations of three-dimensional particle dynamics show that when irradiated by an ultrashort intense laser pulse, the deuterated methane cluster expands and the majority of deuterons overrun the more slowly expanding carbon ions, resulting in the creation of two separated subclusters. The enhanced deuteron kinetic energy and a narrow peak around the energy maximum in the deuteron energy distribution make a considerable contribution to the efficiency of nuclear fusion compared with the case of homonuclear deuterium clusters. With the intense laser irradiation, the nuclear fusion yield increases with the increase of the cluster size, so that deuterated heteronuclear clusters with larger sizes are required to achieve a greater neutron yield.

New directions in sparse sampling and estimation for underdetermined systems

A central objective in signal processing is to infer meaningful information from a set of measurements or data. While most signal models have an overdetermined structure (the number of unknowns less than the number of equations), traditionally very few statistical estimation problems have considered a data model which is underdetermined (number of unknowns more than the number of equations). However, in recent times, an explosion of theoretical and computational methods have been developed primarily to study underdetermined systems by imposing sparsity on the unknown variables. This is motivated by the observation that inspite of the huge volume of data that arises in sensor networks, genomics, imaging, particle physics, web search etc., their information content is often much smaller compared to the number of raw measurements. This has given rise to the possibility of reducing the number of measurements by down sampling the data, which automatically gives rise to underdetermined systems.

In this thesis, we provide new directions for estimation in an underdetermined system, both for a class of parameter estimation problems and also for the problem of sparse recovery in compressive sensing. There are two main contributions of the thesis: design of new sampling and statistical estimation algorithms for array processing, and development of improved guarantees for sparse reconstruction by introducing a statistical framework to the recovery problem.

We consider underdetermined observation models in array processing where the number of unknown sources simultaneously received by the array can be considerably larger than the number of physical sensors. We study new sparse spatial sampling schemes (array geometries) as well as propose new recovery algorithms that can exploit priors on the unknown signals and unambiguously identify all the sources. The proposed sampling structure is generic enough to be extended to multiple dimensions as well as to exploit different kinds of priors in the model such as correlation, higher order moments, etc.

Recognizing the role of correlation priors and suitable sampling schemes for underdetermined estimation in array processing, we introduce a correlation aware framework for recovering sparse support in compressive sensing. We show that it is possible to strictly increase the size of the recoverable sparse support using this framework provided the measurement matrix is suitably designed. The proposed nested and coprime arrays are shown to be appropriate candidates in this regard. We also provide new guarantees for convex and greedy formulations of the support recovery problem and demonstrate that it is possible to strictly improve upon existing guarantees.

This new paradigm of underdetermined estimation that explicitly establishes the fundamental interplay between sampling, statistical priors and the underlying sparsity, leads to exciting future research directions in a variety of application areas, and also gives rise to new questions that can lead to stand-alone theoretical results in their own right.

Pure Coulomb explosions of highly charged methane clusters investigated by a simple electrostatic model

The pure Coulomb explosions of the methane clusters (CA(4))(n), (light atom A = H or D) have been investigated by a simplified electrostatic model for both a single cluster and an ensemble of clusters with a given cluster size distribution. The dependence of the energy of ions produced from the explosions on cluster size and the charge state of the carbon ions has been analysed. It is found that, unlike the average proton energy which increases with the charge q of the carbon ions, the average deuteron energy tends to saturate as q becomes larger than 4. This implies that when the laser intensity is sufficiently high for the (CD4)(n) to be ionized to a charge state of (C4+D4+)(n), the neutron yield from a table-top laser-driven Coulomb explosion of deuterated methane clusters (CD4)(n) could be increased significantly by increasing the interaction volume rather than by increasing the laser intensity to produce the higher charge state (C6+D4+)(n). The flight-time spectra of the carbon ions and the light ions have also been studied.