18,077 research outputs found

    Quantum dots based superluminescent diodes and photonic crystal surface emitting lasers

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    This thesis reports the design, fabrication, and electrical and optical characterisations of GaAs-based quantum dot (QD) photonic devices, specifically focusing on superluminescent diodes (SLDs) and photonic crystal surface-emitting lasers (PCSELs). The integration of QD active regions in these devices is advantageous due to their characteristics such as temperature insensitivity, feedback insensitivity, and ability to utilise the ground state (GS) and excited state (ES) of the dots. In an initial study concerning the fabrication of QD-SLDs, the influence of ridge waveguide etch depth on the electrical and optical properties of the devices are investigated. It is shown that the output power and modal gain from shallow etched ridge waveguide is higher than those of deep etched waveguides. Subsequently, the thermal performance of the devices is analysed. With increased temperature over 170 ºC, the spectral bandwidth is dramatically increased by thermally excited carrier transition in excited states of the dots. Following this, an investigation of a high dot density hybrid quantum well/ quantum dot (QW/QD) active structure for broadband, high-modal gain SLDs is presented. The influence of the number of QD layers on the modal gain of hybrid QW/QD structures is analysed. It is shown that higher number of dot layer provides higher modal gain value, however, there is lack of emission from QW due to the requirement of large number of carriers to saturate the QD. Additionally, a comparison is made between “unchirped QD” and “ chirped QD” of hybrid QW/QD structure in terms of modal gain and spectral bandwidth. It is showed that “chirped” of the QD can improve the “flatness” of the spectral bandwidth. Lastly, the use of self-assembled InAs QD as the active material in epitaxially regrown GaAs-based PCSELs is explored for the first time. Initially, it is shown that both GS and ES lasing can be achieved for QD-PCSELs by changing the grating period of the photonic crystal (PC). The careful design of these grating periods allows lasing from neighbouring devices at GS ( ~1230 nm) and ES (~1140 nm), 90 nm apart in wavelength. Following this, the effect of device area, PC etch depth, PC atom shape (circle or triangle or orientation) on lasing performance is presented. It is shown that lower threshold current density and higher slope efficiencies is achieved with increasing the device size. The deeper PC height device has higher output power due to more suitable height and minimal distance to active region. The triangular atom shape has slightly higher slope efficiency compared to triangular atom shape which is attributed to breaking in-plane symmetry and increase out-of-plane emission

    Comparison of different gene-therapy methods to treat Leber hereditary optic neuropathy in a mouse model

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    IntroductionTherapies for Leber hereditary optic neuropathy (LHON), in common with all disorders caused by mutated mitochondrial DNA, are inadequate. We have developed two gene therapy strategies for the disease: mitochondrial-targeted and allotopic expressed and compared them in a mouse model of LHON.MethodsA LHON mouse model was generated by intravitreal injection of a mitochondrialtargeted Adeno-associated virus (AAV) carrying mutant human NADH dehydrogenase 4 gene (hND4/m.11778G>A) to induce retinal ganglion cell (RGC) degeneration and axon loss, the hallmark of the human disease. We then attempted to rescue those mice using a second intravitreal injection of either mitochondrial-targeted or allotopic expressed wildtype human ND4. The rescue of RGCs and their axons were assessed using serial pattern electroretinogram (PERG) and transmission electron microscopy.ResultsCompared to non-rescued LHON controls where PERG amplitude was much reduced, both strategies significantly preserved PERG amplitude over 15 months. However, the rescue effect was more marked with mitochondrial-targeted therapy than with allotopic therapy (p = 0.0128). Post-mortem analysis showed that mitochondrial-targeted human ND4 better preserved small axons that are preferentially lost in human LHON.ConclusionsThese results in a pre-clinical mouse model of LHON suggest that mitochondrially-targeted AAV gene therapy, compared to allotopic AAV gene therapy, is more efficient in rescuing the LHON phenotype

    Estimulación de la médula espinal en dolor neuropático refractario en adultos: evaluación de la eficacia, efectividad, seguridad y eficiencia en la neuropatía diabética dolorosa y los síndromes de la cirugía fallida de columna y de dolor regional complejo

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    Medul·la espinal; Dolor neuropàtic; Estimulació elèctricaMédula espinal; Dolor neuropático; Estimulación eléctricaSpinal cord; Neuropathic pain; Electrical stimulationAquest informe té com a objectiu avaluar la seguretat, l’eficàcia/efectivitat i el cost-efectivitat de la SCS en adults per al tractament del dolor neuropàtic refractari associat a la neuropatia diabètica dolorosa (NDD) i a les síndromes de fallida de la cirurgia d’esquena (FBSS per les seves sigles en anglès, failed back surgery syndrome) i de dolor regional complex (CRPS per les seves sigles en anglès, complex regional pain syndrome) com a tècnica coadjuvant i en comparació amb els tractaments convencionals.Este informe tiene el objectivo de evaluar la seguridad, la eficacia/efectividad y el coste-efectividad de la SCS en adultos para el tratamiento del dolor neuropático refractario asociado a la neuropatía diabética dolorosa (NDD) y a los síndromes de la cirugía fallida de columna (FBSS por sus siglas en inglés, failed back surgery syndrome) y de dolor regional complejo (CRPS por sus siglas en inglés, complex regional pain syndrome) como técnica coadyuvante y en comparación con los tratamientos convencionales.The aim of this HTA report is to evaluate the safety, efficacy/effectiveness and cost-effectiveness of SCS in adults to treat refractory neuropathic pain associated with painful diabetic neuropathy (PDN, NDD in Spanish), failed back surgery syndrome (FBSS), and complex regional pain syndrome (CRPS) as an adjuvant technique and in comparison with conventional treatments

    EVALUACIÓN ANALGÉSICA PERIOPERATORIA DEL ACETAMINOFÉN EN PERRAS SOMETIDAS A OVARIOHISTERECTOMÍA ELECTIVA

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    Tesis de doctorado que evalúa el efecto analgésico del acetaminofén en perras ovarihisterectomizadas.La administración de analgésicos antiinflamatorios no esteroidales (AINES) para el control del dolor post-quirúrgico en perros es una práctica común, debido a sus efectos analgésicos, antiinflamatorios y antipiréticos. En el presente trabajo se realizaron dos estudios. En el experimento 1, el objetivo fue evaluar la analgesia post-operatoria del acetaminofén (paracetamol) a través de la utilización de las escalas de reconocimiento clínico del dolor DIVAS (Escala Dinámica e Interactiva Analógica Visual) y UMPS (Escala de la Universidad de Melbourne), en perras sometidas a ovariohisterectomía electiva. Además de valorar la seguridad y eficacia clínica del uso del acetaminofén en perros mediante pruebas de funcionamiento hepático y renal en el post-operatorio inmediato. Para ello, se utilizaron 30 perras de diferentes razas que fueron asignadas aleatoriamente a uno de los tres grupos de tratamiento: acetaminofén [GACET; n=10, 15 mg kg-1 intravenoso (IV)], carprofeno (GCARP; n=10, 4 mg kg-1 IV) y meloxicam (GMELOX; n=10, 0.2 mg kg-1 IV). Todos los tratamientos se administraron 30 minutos antes de la cirugía y posterior a esta durante 48 horas. En este período el acetaminofén se administró por vía oral cada 8 horas (15 mg kg-1); el carprofeno (4 mg kg-1) y el meloxicam (0.1 mg kg-1) se administraron por vía IV cada 24 horas. Durante el postoperatorio, los sistemas de puntuación del dolor DIVAS y UMPS fueron medidos a las 1, 2, 4, 6, 8, 12, 16, 20, 24, 36 y 48 horas post-cirugía. Para evaluar la seguridad clínica de los tratamientos, se recolectaron muestras de sangre de la vena yugular para realizar la medición de enzimas ALT, AST, ALP, y los metabolitos bilirrubina directa, bilirrubina indirecta, bilirrubina total, creatinina, urea, albúmina y glucosa. Esto fue realizado en T0 (pre-anestesia; TBASAL), 48 y 96 horas después de la cirugía (T48, T96). Los resultados indican que en la evaluación clínica del dolor de todos los grupos de estudio, hubo una reducción gradual en la percepción del mismo durante el postoperatorio en ambos sistemas de puntuación; no obstante, también fue observado que ninguna escala difirió significativamente entre los tres grupos de tratamiento (P>0.05) en cada momento de evaluación durante las 48 horas post-cirugía. En cuanto a los parámetros bioquímico séricos, sólo la ALT aumentó significativamente en T96 en el GACET y GCARP con respecto a los valores basales (P<0.01). El resto de los analitos séricos evaluados se mantuvo en rangos normales. En el experimento 2 bajo el mismo diseño experimental de tratamientos administrados, el objetivo fue evaluar el efecto analgésico perioperatorio del acetaminofén 2 administrado pre y post-quirúrgicamente en perras sometidas a ovariohisterectomía electiva a través de la medición del índice de la actividad del tono parasimpático (PTA). Este parámetro hemodinámico fue medido 60 minutos antes de la cirugía (TBASAL) y durante el transquirúrgico en la aplicación de estímulos nociceptivos: colocación de las pinzas de campo backhouse (TPINZ), incisión de piel y abordaje quirúrgico primario (TINC), ligadura y extracción de pedículo ovárico izquierdo (TOVI) y derecho (TOVD), ligadura y transfixión del cuello uterino (TLIGUT), sección quirúrgica del cuello uterino (TCUT), reconstrucción de peritoneo y planos anatómicos musculares (TMUSC) y sutura de piel (TSUT). Durante el postoperatorio, el índice PTA fue valorado a las 1, 2, 4, 6, 8, 12, 16, 20, 24, 36 y 48 horas, en los mismos tiempos en que fueron evaluadas las escalas de reconocimiento de dolor DIVAS y UMPS. Los resultados obtenidos en la medición del índice PTA basal para GACET fue 65 ± 8, para GCARP 65 ± 7 y para GMELOX 62 ± 5. Durante los diferentes tiempos transquirúrgicos, los valores promedio de índice PTA indican que GACET (76 ± 14) y GMELOX (72 ± 18) muestran tendencia a manifestar mayores niveles en comparación con GCARP (62 ± 13) desde el inicio del procedimiento quirúrgico sin que esto pudiera comprobarse estadísticamente, ya que no hubo diferencias significativas entre grupos de tratamiento ni entre los tiempos quirúrgicos evaluados (P>0.05). En el postoperatorio, el índice PTA fue de 65 ± 9 en el GACET, 63 ± 8 en el GCARP y 65 ± 8 en el GMELOX. Los resultados tampoco mostraron diferencias estadísticamente significativas con los valores basales o entre los tratamientos (P>0.05). El índice PTA postoperatorio mostró una sensibilidad del 40%, especificidad del 98.46% y valor predictivo negativo del 99.07% con respecto a la escala validada de UMPS. En conclusión, el acetaminofén puede considerarse una herramienta para el tratamiento efectivo del dolor perioperatorio agudo en perros, ya que mostró la misma eficacia clínica que el meloxicam y el carprofeno para la analgesia postquirúrgica en perras sometidas a ovariohisterectomía electiva. Además, la evidencia del uso de este medicamento no condujo a reacciones adversas o cambios en los parámetros evaluados, lo que indica su seguridad clínica. Finalmente, destacar que el índice PTA representa una medición objetiva del comfort y analgesia postoperatoria, por lo que es una herramienta que podría ayudar a predecir las respuestas hemodinámicas asociadas con el dolor

    Exploring differences in electromyography and force production between front and back squats before and after fatigue and how this differs between the sexes

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    Limited research has been conducted to explore sex differences in biomechanical and physiological demands of the front and back squat, especially in response to fatigue where technique may be altered. Therefore, this study investigated differences in electromyography and force production in performance of back and front squats before and after a fatigue protocol and how this differed between males and females. 35 participants (5 female, 30 male) performed a fatigue protocol for back and front squats with measures of maximal performance pre and post. Main findings were that mean and peak activation of the semitendinosus was greater in the back squat than the front squat suggesting that the back squat has greater hamstring activation possibly for hip stabilisation and knee flexion (p < 0.05). There were no differences in quadricep activation between back and front squats, disputing the notion that front squats have a greater quadricep focus, however, lending support to the hypothesis that quadricep activation equal to the back squat can be achieved with lighter absolute load in a front squat. There were no differences in electromyography as a result of fatigue however force production decreased for back squats following fatigue (p < 0.01). This decrease could result from decreased acceleration out of the bottom position and into the concentric phase. This study also presents preliminary findings of greater mean and peak rectus femoris activation in females compared to males in both front (p < 0.01) and back squats (p < 0.05). This was suggested to be in order to support the knee and in an attempt to prevent knee valgus and excess hip adduction. These findings have implications in programming for both high performance sport and for rehabilitation of lower limb injuries

    Electrochemical degradation of methylene blue using Ce(Iv) ionic mediator in the presence of Ag(I) ion catalyst for environmental remediation

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    Methylene blue (MB) is often used in textile industries and is actively present in the wastewater runs-off. Recently, mediated electrochemical oxidation (MEO) offers a fast, reliable and promising results for environmental remediation. Thus, we aimed to evaluate the electro-degradation potential of MB by MEO using Ce(IV) ionic mediator. Furthermore, we also observed the influence of addition Ag(I) ion catalyst in MEO for degradation of MB. The electro-degradation of MB was evaluated by cyclic voltammetry technique and was confirmed by UV-Vis spectrophotometry, high performance liquid chromatography (HPLC) analysis and back-titration analysis. The results showed that in the absence of Ag(I) ion catalyst, about 89 % of MB was decolorized within 30 min. When 2 mM of Ag(I) ion catalyst was applied, the electro-degradation of MB was increased to maximum value of 100%. The UV-Vis spectrum confirmed the electro-degradation of MB as suggested by decreased maximum absorbance value at λ 668 nm from 2.125 to 0.059. The HPLC analysis showed the formation of five new peaks at retention time of 1.331, 1.495, 1.757, 1.908, and 2.017 min, confirming the electro-degradation of MB. The back-titration analysis showed about 52.9% of CO2 was produced during electro-degradation of MB by MEO. More importantly, more than 97% of Ce(IV) ionic mediator were recovered in our investigation. Our results showed the potential of MEO using Ce(IV) ionic mediator to improve the wastewater runs-off quality from textile as well as other industries containing methylene blue

    Towards A Graphene Chip System For Blood Clotting Disease Diagnostics

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    Point of care diagnostics (POCD) allows the rapid, accurate measurement of analytes near to a patient. This enables faster clinical decision making and can lead to earlier diagnosis and better patient monitoring and treatment. However, despite many prospective POCD devices being developed for a wide range of diseases this promised technology is yet to be translated to a clinical setting due to the lack of a cost-effective biosensing platform.This thesis focuses on the development of a highly sensitive, low cost and scalable biosensor platform that combines graphene with semiconductor fabrication tech-niques to create graphene field-effect transistors biosensor. The key challenges of designing and fabricating a graphene-based biosensor are addressed. This work fo-cuses on a specific platform for blood clotting disease diagnostics, but the platform has the capability of being applied to any disease with a detectable biomarker.Multiple sensor designs were tested during this work that maximised sensor ef-ficiency and costs for different applications. The multiplex design enabled different graphene channels on the same chip to be functionalised with unique chemistry. The Inverted MOSFET design was created, which allows for back gated measurements to be performed whilst keeping the graphene channel open for functionalisation. The Shared Source and Matrix design maximises the total number of sensing channels per chip, resulting in the most cost-effective fabrication approach for a graphene-based sensor (decreasing cost per channel from £9.72 to £4.11).The challenge of integrating graphene into a semiconductor fabrication process is also addressed through the development of a novel vacuum transfer method-ology that allows photoresist free transfer. The two main fabrication processes; graphene supplied on the wafer “Pre-Transfer” and graphene transferred after met-allisation “Post-Transfer” were compared in terms of graphene channel resistance and graphene end quality (defect density and photoresist). The Post-Transfer pro-cess higher quality (less damage, residue and doping, confirmed by Raman spec-troscopy).Following sensor fabrication, the next stages of creating a sensor platform involve the passivation and packaging of the sensor chip. Different approaches using dielec-tric deposition approaches are compared for passivation. Molecular Vapour Deposi-tion (MVD) deposited Al2O3 was shown to produce graphene channels with lower damage than unprocessed graphene, and also improves graphene doping bringing the Dirac point of the graphene close to 0 V. The packaging integration of microfluidics is investigated comparing traditional soft lithography approaches and the new 3D printed microfluidic approach. Specific microfluidic packaging for blood separation towards a blood sampling point of care sensor is examined to identify the laminar approach for lower blood cell count, as a method of pre-processing the blood sample before sensing.To test the sensitivity of the Post-Transfer MVD passivated graphene sensor de-veloped in this work, real-time IV measurements were performed to identify throm-bin protein binding in real-time on the graphene surface. The sensor was function-alised using a thrombin specific aptamer solution and real-time IV measurements were performed on the functionalised graphene sensor with a range of biologically relevant protein concentrations. The resulting sensitivity of the graphene sensor was in the 1-100 pg/ml concentration range, producing a resistance change of 0.2% per pg/ml. Specificity was confirmed using a non-thrombin specific aptamer as the neg-ative control. These results indicate that the graphene sensor platform developed in this thesis has the potential as a highly sensitive POCD. The processes developed here can be used to develop graphene sensors for multiple biomarkers in the future

    Assessment of partial discharge activity and conductivity in IGBT modules as a reliability index

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    Al giorno d’oggi l’elettronica di potenza deve essere in grado di operare in ambienti ostili e in condizioni di lavoro difficili. Il tema dell’affidabilità è diventato fondamentale quanto quello dell’efficienza. Questa tesi si focalizza sull’IGBT, in particolare sul suo sistema d’isolamento. Il primo passo è stato studiare in dettaglio i meccanismi di guasto possibili e più frequenti. Dal momento che le scariche parziali risultano essere un problema per l’affidabilità dei dielettrici solidi, in questo studio si esamina l’attività di PD su moduli IGBT nuovi ed invecchiati, in diverse configurazioni, con forme d’onda di tensione e temperature differenti. Si sono effettuate anche misure di corrente di dispersione su moduli nuovi ed invecchiati alla temperatura di lavoro. I risultati sono stati post-processati statisticamente tentando di ottenere indici di affidabilità per quei moduli. Quasi tutti i moduli invecchiati sono interessati da PD e i risultati mostrano che il PDIV, assieme ad altri fattori, è sicuramente influenzato dall’ageing. I risultati del monitoraggio della corrente di dispersione mostrano una tendenza all'aumento con l'invecchiamento. Si sono svolte anche simulazioni con software agli elementi finiti e rilevazioni ottiche di PD ed entrambe supportano i risultati ottenuti. È necessario effettuare ulteriori indagini su un data set più ampio al fine di migliorare un algoritmo di diagnostica predittiva basato sui valori di PDIV e conducibilità
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