Enhanced crystallization and phase transformation of amorphous silicon nitride under high pressure

The crystallization and phase transformation of amorphous Si3N4 ceramics under high pressure (1.0-5.0 GPa) between 800 and 1700 degreesC were investigated. A greatly enhanced crystallization and alpha-beta transformation of the amorphous Si3N4 ceramics were evident under the high pressure, as characterized by that, at 5.0 GPa, the amorphous Si3N4, began to crystallize at a temperature as low as 1000 degreesC (to transform to alpha modification). The subsequent alpha-beta transformation occurred completed between 1350 and 1420 degreesC after only 20 min of pressing at 5.0 GPa. In contrast, under 0.1 MPa N-2, the identical amorphous materials were stable up to 1400 degreesC without detectable crystallization, and only a small amount of a phase was detected at 1500 degreesC. The crystallization temperature and the alpha-beta transformation temperatures are reduced by 200-350 degreesC compared to that at normal pressure. The enhanced phase transformations of the amorphous Si3N4, were discussed on the basis of thermodynamic and kinetic consideration of the effects of pressure on nucleation and growth.

Electrochemical Synthesis of Barium Tungstate Crystallites with Different Morphologies: Effect of Electrolyte Components

Barium tungstate crystallites with different sizes and morphologies were successfully synthesized using a simple electro-chemical technique by varying the components of electrolyte solutions. XRD analysis evidenced that the as-prepared samples were a pure tetragonal-phase of BaWO4 with a scheelite structure. Scanning electron microscopy images and PL spectra of BaWO4 crystallites revealed that the presence of OH- ions and the incorporation of absolute ethanol into the electrolyte solution would have important effects on their particle sizes, morphologies, and optical properties.

Synthesis of NiWO4 nano-particles in low-temperature molten salt medium

Nickel tungstate (NiWO4) nano-particles were successfully synthesized at low temperatures by a molten salt method, and characterized by Xray diffraction (XRD), transmission electron microscopy (TEM) and ultraviolet visible spectra techniques (UV-vis), respectively. The effects of calcining temperature and salt quantity on the crystallization and development of NiWO4 crystallites were studied. Experimental results showed that the well-crystallized NiWO4 nano-particles with about 30 nm in diameter could be prepared at 270 degrees C with 6:1 mass ratio of the salt to NiWO4 precursor. XRD analysis confirmed that the product was a pure monoclinic phase of NiWO4 with wolframite structure. UV-vis spectrum revealed that NiWO4 nano-particles had good light absorption properties in both ultraviolet and visible light region. (C) 2009 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

机器人化纳米操作系统驱动器驱动与探针定位研究

对基于AFM的机器人化纳米操作系统而言,一个关键问题是如何实现纳米操作时探针的高精度驱动与定位。对此,本文基于对压电陶瓷驱动器的迟滞/非线性特性及现有驱动方法的详细分析,提出"基于复现扫描轨迹的驱动方法"来对操作时的驱动器进行驱动;另外,还对管式驱动器弯曲运动所产生的运动学耦合误差、探针悬臂变形所引起的针尖偏移误差进行了定量分析与补偿。采用上述驱动方法及进行误差补偿后,可以大大提高探针的定位精度,从而使纳米操作与装配得以高精度进行。纳米刻画实验验证了该新型驱动方法及误差补偿的有效性。

机器人化纳米操作中任务空间的实时反馈方法研究

纳米科技的最终目标是在原子、分子尺度上，制造具有新颖物理、化学和生物特性的器件和系统，而实现这个目标最为关键的使能技术便是纳米尺度下进行观测、操作和装配的科学方法与相关技术手段。原子力显微镜（AFM：Atomic Force Microscopy）的发明为实现这一目标提供了可行途径，AFM除了能够在常态下实现对原子、分子尺度大小物体的观测，并且由于其超高的分辨率和运动精度，可控、可重复的运动方式，独特的机械力作用机理，任意环境的可适应性而广泛应用于纳米操作。然而AFM的主要功能是进行纳米观测，应用于纳米操作时面临着许多挑战性的难题，尽管随着近十年的深入研究，一些问题已经得到了部分解决，但是缺乏高可信度的实时视觉反馈、无法实现任务空间内探针的精确定位依然阻碍着AFM纳米操作的效率。以目前最为先进的AFM纳米操作方法—增强现实技术为例，尽管该技术可以为操作者提供实时的视觉反馈，但是这种视觉反馈并不代表纳米操作场景的真实变化，而是根据离线模型计算得到的一种图形仿真，因而视觉反馈是否可信取决于模型的准确程度，然而受纳米尺度下各种非线性力的影响，如毛细力、范德华力、静电力等等，很难建立完全精确的物理模型，模型误差将导致错误的视觉反馈并引起纳米操作的失败。此外，受PZT非线性和温漂的影响，基于AFM的纳米操作还缺乏在任务空间内对探针进行精确定位的能力，导致操作过程中AFM探针无法有效接触到纳米物体，使得机器人学中“从A点运动到B点”最为基本的任务难以实现，这些缺点都严重阻碍着AFM纳米操作的效率和效果。本论文针对上述问题，以机器人学中的感知、决策、行为理论和监控方法为基础，具体开展了以下几方面的工作： 1、视觉反馈缺乏可信度是基于增强现实AFM纳米操作面临的主要问题，由于操作者无法对视觉反馈可信度作出评断，经常会在错误视觉反馈的指引下进行无效的纳米操作，从而浪费大量的时间，降低了AFM纳米操作的效率。为了克服上述问题，本文在研究信息诊断与反馈理论基础上，提出了基于Kalman滤波的视觉反馈可信度在线监控方法，实现了视觉反馈错误的实时检测，避免了无效纳米操作的发生，提高了AFM纳米操作的效率。 2、错误视觉反馈被检测出后，需要对其修正以保证纳米操作任务的成功完成。然而传统修正方法需要中断纳米操作进行重新扫描成像，这往往需要耗费几分钟的时间，严重降低了AFM纳米操作的效率。针对该问题，本文提出一种基于局部扫描的在线修正方法，通过扫描轨迹的优化，该方法能够对真实纳米操作结果进行实时感知，从而不需要中断纳米操作就能实现错误视觉反馈的修正，并使得整个修正过程对于操作者透明。这保证了实时可视监控信息的真实性，显著提升了AFM纳米操作的效率。 3、PZT非线性和随机漂移是影响AFM探针精确定位的主要因素，针对该问题本文提出了一种基于路标的探针定位方法，其核心思想是不再采用距离为测度方式进行探针位置描述，而是将作业区域的特定形貌特征定义为参考路标，通过探针对特征形貌的主动感知实现基于路标地图的探针定位，有效消除PZT非线性和随机漂移引起的定位误差，提高探针在任务空间内的定位精度。 4、研究了机器人化纳米操作系统任务空间实时反馈的构建技术，具体包括高灵敏度纳米操作力的感知方法，系统结构误差的产生原因和补偿策略，面向探针实时运动控制的系统结构设计，系统的软硬件实现方案等内容，并利用该实验平台开展了大量实验研究，验证了本论文所提出理论方法的正确性，同时演示性地组建了基于单根CNT和DNA的纳电子器件，实验结果表明AFM纳米操作的效率和效果得到了极大提升。本文的研究工作丰富了基于AFM的机器人化纳米操作理论，为基于AFM的纳米制造技术发展提供了具有一定指导意义的理论方法和研究途径。

纳米级微动平台的设计与实验研究

纳米级微动平台（以下简称微动平台）是微机电系统的重要组成部分，其技术涵盖多个领域的先进技术，其应用范围和领域也越来越广泛。微动平台是实现纳米尺度观测与操作的关键部件。纳米级微动平台的机械性能如力学和运动学特性，直接影响纳米作业系统的应用效果。本文以纳米级微动平台的设计开发为目标，采用CAD和CAE技术，以机械设计理论、有限元方法、显微视觉检测技术等为研究手段，较深入地研究了一种基于PZT驱动的非耦合2维纳米级微动平台的结构设计、结构力学特性以及运动精度等关键技术问题。为此类纳米级微动平台的设计、加工、组装与测试提供了基本理论依据和实现途径。主要工作如下： 1 针对非耦合纳米级微动平台的应用背景和技术要求，应用CAD和CAE技术完成了基于弹性筋板导向和压电陶瓷驱动的新型纳米级微动平台的结构设计。 2 研究采用有限元分析软件ANSYS和COSMOSWorks对所设计的纳米级微动平台进行了结构力学仿真分析，理论上证明了平台结构设计的合理性及可行性。 3 针对驱动器装配误差、导向筋板的加工误差对平台运动精度的影响问题，研究采用有限元仿真方法对平台的运动精度进行了定量的计算分析。 4 研究采用显微视觉技术和序列图像处理技术，完成了纳米级微动平台动态运动性能的检测，给出了平台的动态输入输出特性以及运动过程中平台边框的变形情况。

Women Potters: Transforming Traditions

Vincentelli, Moira, Women Potters: Transforming Traditions (London: A and C Black, 2003) RAE2008

Facetas de Porcelana VS Facetas de Resina Composta

Projeto de Pós-Graduação/Dissertação apresentado à Universidade Fernando Pessoa como parte dos requisitos para obtenção do grau de Mestre em Medicina Dentária

Qual a eficácia clínica do sistema CEREC com os seus diferentes materiais para reabilitação em prótese fixa e sobre implantes?

Projeto de Pós-Graduação/Dissertação apresentado à Universidade Fernando Pessoa como parte dos requisitos para obtenção do grau de Mestre em Medicina Dentária

Nanostructured ferroelectric materials

Nanostructured materials are central to the evolution of future electronics and information technologies. Ferroelectrics have already been established as a dominant branch in the electronics sector because of their diverse application range such as ferroelectric memories, ferroelectric tunnel junctions, etc. The on-going dimensional downscaling of materials to allow packing of increased numbers of components onto integrated circuits provides the momentum for the evolution of nanostructured ferroelectric materials and devices. Nanoscaling of ferroelectric materials can result in a modification of their functionality, such as phase transition temperature or Curie temperature (TC), domain dynamics, dielectric constant, coercive field, spontaneous polarisation and piezoelectric response. Furthermore, nanoscaling can be used to form high density arrays of monodomain ferroelectric nanostructures, which is desirable for the miniaturisation of memory devices. This thesis details the use of various types of nanostructuring approaches to fabricate arrays of ferroelectric nanostructures, particularly non-oxide based systems. The introductory chapter reviews some exemplary research breakthroughs in the synthesis, characterisation and applications of nanoscale ferroelectric materials over the last decade, with priority given to novel synthetic strategies. Chapter 2 provides an overview of the experimental methods and characterisation tools used to produce and probe the properties of nanostructured antimony sulphide (Sb2S3), antimony sulpho iodide (SbSI) and lead titanate zirconate (PZT). In particular, Chapter 2 details the general principles of piezoresponse microscopy (PFM). Chapter 3 highlights the fabrication of arrays of Sb2S3 nanowires with variable diameters using newly developed solventless template-based approach. A detailed account of domain imaging and polarisation switching of these nanowire arrays is also provided. Chapter 4 details the preparation of vertically aligned arrays of SbSI nanorods and nanowires using a surface-roughness assisted vapour-phase deposition method. The qualitative and quantitative nanoscale ferroelectric properties of these nanostructures are also discussed. Chapter 5 highlights the fabrication of highly ordered arrays of PZT nanodots using block copolymer self-assembled templates and their ferroelectric characterisation using PFM. Chapter 6 summarises the conclusions drawn from the results reported in chapters 3, 4 and 5 and the future work.

Nonlinear piezoelectricity in electroelastic energy harvesters: Modeling and experimental identification

We propose and experimentally validate a first-principles based model for the nonlinear piezoelectric response of an electroelastic energy harvester. The analysis herein highlights the importance of modeling inherent piezoelectric nonlinearities that are not limited to higher order elastic effects but also include nonlinear coupling to a power harvesting circuit. Furthermore, a nonlinear damping mechanism is shown to accurately restrict the amplitude and bandwidth of the frequency response. The linear piezoelectric modeling framework widely accepted for theoretical investigations is demonstrated to be a weak presumption for near-resonant excitation amplitudes as low as 0.5 g in a prefabricated bimorph whose oscillation amplitudes remain geometrically linear for the full range of experimental tests performed (never exceeding 0.25% of the cantilever overhang length). Nonlinear coefficients are identified via a nonlinear least-squares optimization algorithm that utilizes an approximate analytic solution obtained by the method of harmonic balance. For lead zirconate titanate (PZT-5H), we obtained a fourth order elastic tensor component of c1111p =-3.6673× 1017 N/m2 and a fourth order electroelastic tensor value of e3111 =1.7212× 108 m/V. © 2010 American Institute of Physics.

Phase II Archaeological Excavations at 99 Main Street, 18AP21 (Sign of the Whale), Annapolis, Maryland

Historical Annapolis Foundation (HAF) conducted terrestrial archaeological investigations at site 18AP21 in the city of Annapolis, Maryland. Excavations were carried out at this National Register site ostensibly as a Phase II project to evaluate the site and assess the need for further work. The site is at 99 Main Street in the center of downtown Annapolis, near the Annapolis waterfront. The project was carried out as part of the advanced work for the Annapolis History Center project, to be built in the adjoining buildings of 99 Main and 196 Green Streets. The buildings are the property of the Historic Annapolis Foundation and located in Maryland Research Unit 7. The excavations were undertaken by HAF, and funded by HAFF. The work was conducted for HAF and MHT, who holds an archaeological easement on the property. This preliminary phase of work included stratigraphic excavation of two testpit units. These two units revealed that the site of the existing 99 Main Street building was the location of three previous constructions. The current building at 99 Main Street, built in 1791, was preceded by an earlier brick dwelling, evidenced by a stout pier of bricks, which was attached to a wooden-sided structure that stood on a foundation of brick and stone. Ceramics indicate that these buildings date to the early-middle of the 18th century. A third structure of post-in-ground construction, evidenced by recovery of burned posts and wood fragments, likely existed prior to these, but evidence was scant. These excavations reveal that the site of 18AP21 holds potential for understanding Annapolis's early cultural developments, especially in the area of initial settlement and the origins of waterfront commerce. The assemblage of artifacts recovered includes a broad sample of common 18th century pottery such as creamware and Chinese export porcelain, and also includes some early colonial types such as tin-glazed earthenware and various red-bodied slipwares. The excavations do not provide conclusive evidence of the construction sequence. Consultation with MHT representatives indicates that further work at the site will likely be needed before modifications to the floor of the building can progress.

Modelling and prototyping the conceptual design of 3D CMM micro-probe

This paper details the prototyping of a novel three axial micro probe based on utilisation of piezoelectric sensors and actuators for true three dimensional metrology and measurements at micro- and nanometre scale. Computational mechanics is used first to model and simulate the performance of the conceptual design of the micro-probe. Piezoelectric analysis is conducted to understand performance of three different materials - silicon, glassy carbon, and nickel - and the effect of load parameters (amplitude, frequency, phase angle) on the magnitude of vibrations. Simulations are also used to compare several design options for layout of the lead zirconium titanate (PZT) sensors and to identify the most feasible from fabrication point of view design. The material options for the realisation of the device have been also tested. Direct laser machining was selected as the primary means of production. It is found that a Yb MOPA based fiber laser was capable of providing the necessary precision on glassy carbon (GC), although machining trials on Si and Ni were less successful due to residual thermal effects.To provide the active and sensing elements on the flexures of the probe, PZT thick films are developed and deposited at low temperatures (Lt720 degC) allowing a high quality functional ceramic to be directly integrated with selected materials. Characterisation of the materials has shown that the film has a homogenous and small pore microstructure.

The influence of alkali metal chlorides on the loss of water from glass-ionomer dental cements

The water loss behaviour of a clinical glass-ionomer dental cement has been studied with and without the addition of alkali metal chlorides. Dehydrating conditions were provided by placing specimens in a desiccator over concentrated sulphuric acid. Cements were prepared using either pure water or an aqueous solution of metal chloride (LiCl, NaCl, KCl) at 1.0 mol/dm(3). In addition, NaCl at 0.5 mol/dm(3) was also used to fabricate cements. Disc-shaped specimens of size 6 mm diameter x 2 mm thickness were made, six performulation, and cured at 37 degrees C for 1 hour They were then exposed to desiccating conditions, and the mass measured at regular intervals. All formulations were found to lose water in a diffusion process that equilibrated after approximately 3 weeks. Diffusion coefficients ranged from 2.27 (0.13) x 10(9) with no additive to 1.85 (0.07) x 10(9) m(2)/s with 1.0 mol/dm(3) KCl. For the salts, diffusion coefficients decreased in the order LiCl > NaCl > KCl. There was no statistically significant difference between the diffusion coefficients for 1.0 and 0.5 mol/dm(3) NaCl. For all salts at 1.0 mol/dm(3) and also additive-free cements, equilibrium losses were, with statistical limits, the same, ranging from 6.23 to 6.34%. On the other hand, 0.5 mol/dm(3) NaCl lost significantly more water 7.05%.

Textural and structural properties of bioactive glasses in the system CaO-SiO2

Gel-derived CaO-SiO2 binary glasses of CaO mole fractions 0. 2, 0.3 and 0. 4 have been prepared and characterised. Pore diameter specific pore volume, skeletal density and porosity were found to increase with increasing CaO-content, whereas a concomitant decrease in specific surface area was observed. Si-29 NMR indicated that the 0.2 CaO mole fraction glass consisted of higly polymerized Q(4) and Q(3) silicate species, with some Q(2) units. With increasing CaO mole fraction, these silicate species became progressively depolymerised such that isolated SiO4 tetrahedra were detected within the 0.4 CaO glass matrix. Unusually, the glasses retained a proportion of Q(4) and Q(3) species as the CaO mole fraction was increased. All glass formulations exhibited in vitro bioactivity. The rate of hydroxyapatite precipitation followed the order 0.2 CaO > 0.4 CaO > > 0.3 CaO, an effect that is attributed to differences in the rate of dissolution of calcium from these glasses. This, in turn, appears to be dependent upon the proportion of Ca 21 participating in the formation of the glassy network.