448 research outputs found

    Optical contrast between transparent materials through external modulation of the Faraday effect

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    Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1998.Includes bibliographical references (leaves 99-101)./ Timothy Allman Denison.M.S

    Preparation of ground sections using UV-curable acrylic adhesives

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    Study of ground sections is the most used and, in some respects, still irreplaceable method for examination the microstructure of paleontological and many other hard and friable objects. At the same time, paleontological samples are relatively difficult for preparations of high-quality thin sections. Many techniques and means, particularly embedding media, have been proposed, but they are often hardly accessible, imperfect or insufficiently studied. A promising and easily accessible non-specialized medium, UV-curable acrylic adhesive (glue for glass) was tested for embedding and mounting of objects with diverse mechanical and optical properties. It shows notably good results, in particular durability, reliable adhesion, ease of use and lack of significant birefringence, which makes it especially valuable for polarized light microscopy. Properties of such adhesives are reviewed and compared with properties of epoxy resins and a number of other media. Disadvantages of the adhesives and ways to deal with them are also elucidated. In addition, broadly accessible tools and methods of sawing, embedding, grinding, mounting and other stages of the work are discussed. Efficiency of a number of grinding agents is measured. On the basis of all these results, a technique of making ground sections using easily accessible means was developed and described step by step. The technique was designed for fossil bones, but is applicable to diverse dry samples, including paleontological, neontological and geological ones

    Brillouin confocal microscopy in off-axis configuration

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    Three-dimensional Brillouin confocal microscopy is an imaging modality that correlates with mechanical properties in biological media from subcellular to tissue level. Over the years we developed new approaches to this technique that improve the spectral performance and can measure directly the local refractive index as well as the complex modulus of the sample; to achieve this goal, we probed two co-localized Brillouin scattering geometries. The confocal microscopy setting ensures three-dimensional mapping with high resolution, while the back scattering configuration allows access to the sample from the same side. For these reasons, such an instrument constitutes a new approach in investigating biological phenomena providing both local index of refraction and mechanical information with a single measurement. This technique has been improved in speed and spatial resolution in order to be applied to some specific challenging material characterization such as liquid-liquid phase separation

    Trends of biosensing: plasmonics through miniaturization and quantum sensing

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    Despite being extremely old concepts, plasmonics and surface plasmon resonance-based biosensors have been increasingly popular in the recent two decades due to the growing interest in nanooptics and are now of relevant significance in regards to applications associated with human health. Plasmonics integration into point-of-care devices for health surveillance has enabled significant levels of sensitivity and limit of detection to be achieved and has encouraged the expansion of the fields of study and market niches devoted to the creation of quick and incredibly sensitive label-free detection. The trend reflects in wearable plasmonic sensor development as well as point-of-care applications for widespread applications, demonstrating the potential impact of the new generation of plasmonic biosensors on human well-being through the concepts of personalized medicine and global health. In this context, the aim here is to discuss the potential, limitations, and opportunities for improvement that have arisen as a result of the integration of plasmonics into microsystems and lab-on-chip over the past five years. Recent applications of plasmonic biosensors in microsystems and sensor performance are analyzed. The final analysis focuses on the integration of microfluidics and lab-on-a-chip with quantum plasmonics technology prospecting it as a promising solution for chemical and biological sensing. Here it is underlined how the research in the field of quantum plasmonic sensing for biological applications has flourished over the past decade with the aim to overcome the limits given by quantum fluctuations and noise. The significant advances in nanophotonics, plasmonics and microsystems used to create increasingly effective biosensors would continue to benefit this field if harnessed properly

    Raman spectroscopy, a non-invasive mesurement technique for the detection of counterfeit medicines

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    Tese de mestrado, Engenharia Farmacêutica, Universidade de Lisboa, Faculdade de Farmácia, 2016Perhaps no greater challenge exists for public health, patient safety, and shared global health security, than fake, falsified, fraudulent or poor quality unregulated medicines - also commonly known as “counterfeit medicines” - now endemic in the global drug supply chain (Tim K Mackey & Liang, 2013). Counterfeit medicines pose a serious risk to public health around the world. It is low- and middle-income countries and those in areas of conflict, or civil unrest, with very weak or non-existent health systems that bear the greatest burden of SSFFC (Substandard, Spurious, Falsely labelled, Falsified and Counterfeit) medical products because the cost of legitimate drugs is beyond the reach of much of the population and legal controls are often weak (World Health Organization, 2010). For this purpose, further scientific research and development is called for to design user-friendly, low-cost and robust portable (hand-held) devices and techniques for detecting and identifying counterfeit medicines in real settings (Karunamoorthi, 2014). This dissertation promotes a technique called Raman spectroscopy that has the potential to optimize quality testing for a broad range of medicines. The aim of this dissertation was to study de detection of medicines through its package, for which it was relevant to investigate if there were differences within the package material and how these differences could affect the spectrums of the tablets under analysis. The results revealed that in fact there are variations in package materials that influence the spectrums acquired. These variations can be due to thickness or density variations. Nevertheless, these variations can be easily overcome using preprocessing methods. For this study, calibration tablets of paracetamol, were also made on purpose for experiencing the detection of different concentrations of an API through blister packages. Furthermore, in this investigation, three different probes were used for the measurements: PhAT probe, MKII probe attached to Raman Workstation microscope, and a green laser, to compare results. Results show that it is possible to detect different concentrations of an active ingredient of tablets through a white blister package using Raman spectroscopy, namely the PhAT probe. This equipment can be put in place analysis enabling faster detection of counterfeit medicines, in a non-invasive and non-destructive way that requires no sample preparation and does not need highly specialized personnel for its use. It provides reliable and useful data and it is portable. This is a promising technique for detecting counterfeit medicines and it is relatively low cost.Talvez não exista maior desafio para a saúde pública global do que a existência de medicamentos não regulamentados, de fraca qualidade, falsificados ou fraudulentos – também conhecidos como "medicamentos falsificados" - agora endémicos na cadeia global de abastecimento e distribuição de medicamentos (Tim K Mackey & Liang, 2013). A qualidade dos medicamentos disponíveis varia muito entre diferentes países devido à falta de regulamentos bem definidos e existência de práticas de controlo de qualidade deficientes. Os medicamentos falsificados incluem produtos com as substâncias adequadas ou com ingredientes errados, sem substância ativa, com quantidade insuficientes ou excessiva de substância ativa, ou com rotulagem errada e falsa. Por vezes, os medicamentos podem ser contaminados com outras substâncias ou podem até sofrer degradação química devido a fracas condições de armazenamento por exemplo em ambientes húmidos. Os medicamentos falsificados são amplamente distribuídos e podem ser bastante sofisticados, incluindo embalagens e estratégias de marketing muito convincentes. Os medicamentos falsificados representam um sério risco para a saúde pública em todo o mundo, sendo que a maioria das denúncias estão relacionadas com antibióticos, anti protozoários, hormonas e esteroides. São os países em desenvolvimento e aqueles em áreas de conflito, ou agitação civil, com sistemas de saúde muito fracos ou inexistentes que mais sofrem com produtos médicos “SSFFC” (Substandard, Spurious, Falsely labelled, Falsified and Counterfeit - denominação atribuída pela Organização Mundial de Saúde, para a definição de medicamentos falsificados), uma vez que o custo dos medicamentos legítimos está fora do alcance de grande parte da população e o controlo legal dos medicamentos é muitas vezes fraco (World Health Organization, 2010). Os medicamentos falsificados nestes países aumentaram devido à existência de muitas doenças infecciosas como a malária e a tuberculose. Neste estudo, é dado o exemplo do sistema de vigilância e monitorização da Organização Mundial de Saúde, que utiliza um sistema de inspeção constituído por três níveis: um primeiro nível realizado no local, que inclui uma inspeção visual da embalagem do medicamento em análise e a sua comparação com embalagens de medicamentos originais; um segundo nível, também este realizado no local, que se segue quando existem dúvidas relativamente aos testes realizados no primeiro nível e que inclui uma validação laboratorial utilizando métodos relativamente simples; se ainda assim os resultados forem inconclusivos segue-se o terceiro nível onde o medicamento é enviado para um laboratório forense, fora deste local, onde são realizados testes mais específicos de confirmação. Trata-se de um processe demorado pelo que mais investigação e desenvolvimento científico são requeridos para projetar técnicas de deteção e equipamentos fáceis de utilizar, de baixo custo e que sejam robustos e portáteis permitindo a identificação de medicamentos falsificados rapidamente e no local (Karunamoorthi, 2014). Esta dissertação promove uma técnica chamada espectroscopia Raman, que tem o potencial para otimizar testes de qualidade para uma ampla gama de medicamentos. Quando um feixe de luz interage com matéria, este pode ser transmitido, absorvido ou espalhado. Quando a luz é espalhada a partir de uma molécula, a maioria dos fotões é espalhada elasticamente, sendo que os fotões espalhados têm a mesma energia, frequência e comprimento de onda que os fotões incidentes. Contudo, uma pequena quantidade de luz é espalhada inelasticamente ou seja, a frequências diferentes, e normalmente mais baixas, do que os fotões incidentes. Este é chamado efeito Raman e foi descoberto por Krishna e Raman. Um espectro Raman contém bandas que são características e proporcionais a concentrações específicas de moléculas numa amostra, pelo que a espectroscopia Raman fornece uma boa análise qualitativa e quantitativa. A intensidade do espalhamento Raman é proporcional ao número de moléculas que produzem este espalhamento Raman. Como resultado, a intensidade do espalhamento Raman pode ser utilizada para medir quanto de um material está presente na amostra em análise (análise quantitativa). A forma de um espectro Raman pode ser utilizada para determinar que tipos de vibrações moleculares existem na amostra em análise. Esta informação vibracional pode ser utilizada para identificar materiais numa amostra (análise qualitativa). Diferenças em termos de stress, temperatura, estrutura cristalina, micro-heterogeneidade etc, podem, portanto, frequentemente ser medidas usando a espectroscopia Raman. A espectroscopia Raman é benéfica para diversos tipos de análise quantitativa e qualitativa num vasto número de campos, incluindo investigação química fundamental, ciências da vida (por exemplo, estudos biomédicos in vivo), controlo de processos, ciências forenses e na área farmacêutica. A espectroscopia Raman pode, deste modo, ser utilizada como uma tecnologia não destrutiva, não invasiva e ainda, como uma tecnologia de monitorização à distância. De um modo breve, as vantagens conhecidas da espectroscopia Raman incluem: elevada especificidade química, a capacidade de quantificar múltiplos constituintes numa forma farmacêutica sólida, a capacidade de analisar diferentes polimorfos e formas cristalinas; a elevada velocidade de análise; a ausência de necessidade de preparação da amostra; a ausência de necessidade de utilização de solventes e/ou consumíveis e a natureza de análise não destrutiva em comparação com outras técnicas de análise tradicionais. Portanto, a espectroscopia Raman é uma tecnologia estabelecida para assegurar a qualidade de produtos farmacêuticos permitindo identificar substâncias ativas e dar informação adicional sobre os excipientes, assim como a concentração relativa das substâncias ativas para os excipientes. Estes rácios podem ser a chave para detetar medicamentos falsificados uma vez que os indivíduos que produzem este tipo de produtos frequentemente têm em conta a quantidade da substância ativa mas não são tão precisos com as quantidades exatas de excipientes. Os instrumentos baseados na tecnologia do efeito Raman têm vindo a evoluir ao longo dos anos, passando de espectrómetros tradicionais de laboratório para ferramentas de menores dimensões, mais acessíveis em termos de custo, mais rápidas e eficientes, pelo que a análise de amostras em situações reais (em campo) ou até dentro de embalagens ou contentores, passou de um conceito ideal para uma tecnologia bem estabelecida para diferentes produtos farmacêuticos. O objetivo desta dissertação é explorar a deteção de medicamentos falsificados utilizando técnicas de espectroscopia Raman para uma análise não destrutiva e não invasiva, tendo em vista a sua aplicabilidade em campo (ou seja, em locais como fronteiras ou locais onde se realiza a inspeção e distribuição de medicamentos) e não, em laboratórios com boas condições e equipamentos assim como pessoal especializado. Esta investigação procura estudar a deteção de medicamentos falsificados através da sua embalagem, para a qual foi relevante investigar possíveis diferenças no próprio material de embalagem e o quanto essas diferenças poderiam interferir com os espectros obtidos dos comprimidos em análise. Os resultados revelaram que, de facto, existem variações em materiais de embalagem que influenciam os espectros adquiridos. Estas variações podem dever-se a diferenças de espessura ou densidade no material. Ainda assim, concluiu-se que estas variações podem ser facilmente ultrapassadas através da utilização de métodos de pré-processamento dos espectros. Para este estudo, foram também produzidos comprimidos de paracetamol, no sentido de experimentar a deteção de diferentes concentrações de um princípio ativo, através da sua embalagem. Além disto, nesta dissertação, foram ainda utilizadas três sondas para as mesmas medições: a sonda PhAT, a sonda MKII conectada ao microscópio Raman Workstation, e um laser verde, para comparar os resultados. Os resultados mostram que é possível detetar concentrações diferentes de um princípio ativo em comprimidos, através de um blister branco, utilizando espectroscopia de Raman, mais precisamente, a sonda PhAT. Este equipamento pode ser colocado em qualquer local de análise, permitindo uma deteção rápida dos medicamentos falsificados, de modo não-invasivo e não-destrutivo sem necessitar de preparação prévia da amostra nem de pessoal altamente especializado para a sua utilização. Este equipamento fornece dados confiáveis e é portátil. Esta é uma técnica promissora para a deteção de medicamentos falsificados e apresenta um custo relativamente baixo

    Development of an ultrasonic NDE&T tool for yield detection in steel structures

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    Nondestructive Evaluation and Testing (NDE&T) is a commonly used and rapidly growing field that offers successful solutions for health assessment of structures. NDE&T methods have gained increasing attention in the last few decades especially with the contribution of the advancements in computer and instrumentation technologies. The applications of numerous NDE&T methods in civil engineering mostly focus on material characterization and defect detection. Techniques for nondestructively identifying the stress state in materials, on the other hand, mostly rely on the Theory of Acoustoelasticity. However, the sensitivity and the accuracy of acoustoelasticity are affected by several factors such as the microstructure of the material, temperature conditions, and the type, propagation and polarization directions of the signals used. This dissertation presents the results of an experimental study that investigates the changes in the characteristics of ultrasonic signals due to the applied stresses. Using a specially built testing system, ultrasonic signals were acquired from four different groups of steel specimens subjected to uniaxial tension below and above the yield stress of the material. The experimental database was first analyzed in terms of the acoustoelastic theory. Then, well known Digital Signal Processing (DSP) methods were used to calculate a total of seven time and frequency domain characteristics of the first three echoes of the acquired signals. The investigated time domain parameters were the peak positive amplitudes and the signal energies of the echoes, while the peak amplitude of the Fast Fourier and Chirp-Z Transforms, peak and peak-to-peak amplitudes and the root mean square of the Wavelet coefficients were used for the spectral analyses. Even though the acoustoelastic effects can be very small for certain measurement cases and they can be influenced by several other factors, clear distinctions between prior to and post yielding were observed for all investigated time and frequency domain parameters. The results were further analyzed with statistical methods and Receiver Operating Characteristics (ROC) curves in order to investigate the potential of the presented study for being used as a nondestructive testing tool for yield detection in steel structures

    Integrated optical devices based on liquid crystals embedded in polydimethylsiloxane flexible substrates

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    The contribution of this thesis is to find possible solutions for the creation of interconnections and optical switches to be used in microoptofluidic systems in the frame of the research activities of the Optoelectronic laboratory of the Department of Information Engineering, Electronics and Telecommunications (DIET). The main goal is to explore a new technology for integrated optic based on a low cost technology to produce low driving power devices. Optofluidics is the science which links the field of photonics with microfluidics, for the creation of innovative and state-of-the-art devices. Liquid crystals (LC) can be used for optofluidic applications because they have the possibility to change without external mechanical actions, the average direction of the molecules through the application of electric fields, reorienting the crystal molecules in such a way as to alter their optical properties [1-2]. The research on LC is more than a century old, but only since the ‘80s of the past century these materials were employed in various fields, from flat panel displays used for televisions, tablets, and smartphones, to biomedical and telecommunication applications [3-5]. The results reported in this thesis include simulation, design and preliminary fabrication of optofluidic prototypes based on LC embedded in polydimethylsiloxane (PDMS) channels, defined as LC:PDMS, with co-planar electrodes to control LC molecular orientation and light propagation. Fabrication techniques which were used include microelectronic processes such as lithography, sputtering, evaporation, and electroplating. The simulations were performed through the combined use of COMSOL Multiphysics® and BeamPROP®. I used COMSOL Multiphysics® to determine the positioning of the molecules in a LC:PDMS waveguide. The LC are the core through which light propagates in a PDMS structure. In addition to these simulations, I used COMSOL Multiphysics® to determine the orientation of the LC under the effect of an electric field [6-7] to create low-power optofluidic devices [8], [11]. I used BeamPROP® to explore the optical propagation of various optical devices such as: optical couplers, the zero gap optical coupler, and a multimodal interferometer. All these devices have been simulated through various combinations of geometries which will be extensively explained in the following chapters. The fabrication of prototypes was made in the Microelectronic Technologies laboratory of DIET. The optofluidic prototypes that I designed could be used in interconnection systems on biosensing devices for chemical or biological applications [10-11], wearable [12], or lab on chips [13], which are increasingly being applied in many research fields [14]. Many of these devices need to interface with electronics for processing signals coming from the interaction between the device with molecules, liquids or other biological substances. Moreover it is necessary to create flexible and biocompatible interfaces, whose features are not guaranteed in classic metal tracks. As it will be clear in the first chapter, metal interconnections must be designed with spatial, energy and throughput restrictions. To develop the optofluidic prototypes, I chose to use a combination of two materials for their commercial availability and ease of use: E7 and 5CB LC produced by Merck® as the transmissive medium and PDMS Sylgard 184 produced by Dow Corning® for the cladding [15-16]. The molecules of the LC are anisotropic, whose shape is elongated like that of a cigar. Under appropriate temperature conditions these molecules retain a state of aggregation in which, while retaining some mechanical properties of the fluids, they have the characteristics of crystals such as birefringence or x-ray reflection. These properties are due to two factors that characterize the various phases of LC: the orientational and positional order that vary according to the temperature. E7 was used in its nematic mesophase. The material used for the cladding of my prototypes was PDMS, a thermosetting polymer, flexible, biocompatible, economical, easy to work, and suitable for the creation of optical and optofluidic devices due to its transparency. The thesis is organized in six chapters whose contents are briefly outlined below: • In the first chapter there is a brief description of optofluidics and the transport phenomena of the liquids in the microchannels. The essential parameters for a correct interpretation of the behavior of the materials in the devices will be defined. Some examples of microfluidic devices, Optofluidic Optical Components (OOC) will be mentioned. • In the second chapter, LC’s will be presented, along with their general characteristics and their behavior in the presence of electric fields. An overview of integrated optic devices based on LC will be reported. • In the third chapter the experimental results will be presented concerning the fabrications and the technologies used to obtain electro-optical LC:PDMS waveguides. • The fourth chapter will be dedicated to a brief description of COMSOL Multiphysics® and BeamPROP® simulators, and the implementation of the model of LC channels in PDMS both in 2D and 3D. Also a brief description of Monte Carlo simulations based on Lebwohl-Lasher potential will be mentioned. • In the fifth chapter an LC:PDMS optical directional coupler and the most significant results will be described. • The sixth chapter is dedicated to the multimodal interferometer and its field of application, the theory behind this device and the results obtained from the simulations using the BeamPROP® • In the conclusion, a brief recap of the results obtained in this thesis and future developments will be presented

    Opto-acoustic thin-film transducers for imaging of Brillouin oscillations on living cells

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    In any given media, the speed of sound is considerably slower than speed of light, and the exploration of the acoustic regime in the GHz range gives access to very short acoustic wavelengths. Short acoustic wavelengths is an intriguing path for high resolution live-cell imaging. At low frequencies, ultrasound has proved to be a valuable tool for the mechanical characterisation and imaging of biological tissues. There is much interest in using high frequency ultrasound to investigate single cells due to its mechanical contrast mechanism. Mechanical characterisation of cells has been performed by a number of techniques, such as atomic force microscopy, acoustic microscopy or Brillouin microscopy. Recently, Brillouin oscillations measurements on vegetal and mammal cells have been demonstrated in the GHz range. In this thesis, a method to extend this technique, from the previously reported single point measurements and line scans, into a high resolution acoustic imaging tool is presented. A novel approach based around a three-layered metal-dielectric-metal film is used as a transducer to launch acoustic waves into the cell being studied. The design of this transducer and imaging system is optimised to overcome the vulnerability of a cell to the exposure of laser light and heat without sacrificing the signal to noise ratio. The transducer substrate shields the cell from the laser radiation by detecting in transmission rather than reflection. It also generates acoustic waves efficiently by a careful selection of materials and wavelengths. Facilitates optical detection in transmission due to simplicity of arrangement and aids to dissipate heat away from the cell. The design of the transducers and instrumentation is discussed and Brillouin frequency images (two and three dimensions) on phantom, fixed and living cells are presented
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