Rozprawy doktorskie na temat „Hydrostatic pressure”

AC susceptibility is an important characterisation technique measuring the time dependent magnetisation and dynamics of a magnetic system. It is capable of yielding information on thermodynamic phase transitions, relaxation processes and losses in a variety of interesting magnetic and superconducting materials. In particular it is a powerful probe of the mixed state of superconductivity providing insight into the ux dynamics at play and determination of a number of physical properties such as the critical temperature Tc, field Hc and characteristic length scales. Application of pressure can tune materials through multiple phases and interesting phenomena. The thesis describes the design of a calibratable susceptometer in a piston cylinder pressure cell, achieving AC susceptibility measurements of the same accuracy as a SQUID magnetometer but under pressure. This is used to make measurements on an electrostatically doped capacitance device, a single chain magnet and a heavy fermion superconductor. These studies are summarised below. Electric double layer (EDL) devices provide a means of continuous tuning through a materials phase diagram by applying an electric field, including inducing superconductivity. Application of pressure in tandem with electrostatic doping could improve the efficiency of these devices and provide a second tuning parameter. An EDL capacitor was constructed and measured with the above susceptometer aiming to shift the Tc of a doped high temperature superconducting cuprate La1:9Sr0:1CuO4. The Tc shifts proved irreproducible already at ambient conditions. Indeed during the course of this research further experimental evidence emerged in the literature indicating EDL devices may very well work due to electrochemical doping rather than electrostatic, possibly accounting for the lack of repeatability. Work therefore focused on mapping the ionic liquid DEME-TFSI's glass-liquid phase diagram over the 1 GPa pressure range, rather than extending the study of the EDLC device to high pressure. Single chain magnets (SCM) are an interesting class of material consisting of a one-dimensional molecular magnet chain manifesting magnetic hysteresis and slow relaxation best characterised by AC susceptibility. The susceptometer was used to study the SCM [Co(NCS)2(pyridine)2]n to investigate the effect of pressure on its characteristic magnetic relaxation time and energy barrier. A secondary signal appears at ~0.44 GPa which is attributed to the development of an additional structural phase that has been independently observed in X-ray crystallographic measurements. The heavy fermion superconductor U6Fe has the highest Tc ~4 K of all the U-based compounds and large critical fields of ~10-12.5 T, depending on direction, which increase on initial application of pressure. It exhibits a coexisting charge density wave (CDW) below 10 K making it a promising candidate for the modulated superconductivity of the theorised Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) state. A feature at 110 K is also evident in Mossbauer, resistivity and specific heat measurements, the origin of which has not yet been clearly identified. Evidence for the FFLO state was sought by mapping the upper critical field Hc2 along with the peak effect through AC susceptibility measurements up to pressures of 1 GPa. The data is accounted for by an evolution of collective pinning and superconducting parameters, with no clear evidence for an FFLO state although an enhancement of the reduced field is observed.

El consum habitual de fruita (com el kiwi) en la dieta té un efecte molt beneficiós per a la salut. No només és una excel·lent font de vitamines, fibra i minerals, sinó que a més posseeix compostos fitoquímics que contribueixen a la salut. D'altra banda, cada dia més els consumidors demanen d'aliments de preparació ràpida, amb una alta qualitat nutritiva, sensorial i el mínim d'additius per a la seva conservació. RESUM La primera impressió que els consumidors reben de les fruites és l'aparença o aspecte extern, sent la més important per a la seva acceptació i decisió de compra. La forma i mida és un dels aspectes més fàcilment discernibles, tot i que generalment no és un caràcter de qualitat decisiu. Només en cas de malformacions o defectes morfològics podria ser-ho. Durant i després de la collita del kiwi, un cert percentatge de la collita no pot ser destinat a la seva distribució ja que no arriba als estàndards de comercialització. D'altra banda, hi ha un sector de població que necessita de facilitats a l'hora d'incentivar el consum de fruites, i en concret de kiwis, com són els nens, els ancians i certs sectors per las quals, per motius de treball o pràctics, és un inconvenient el rentar, pelar i tallar certes fruites fora de casa. En base a aquest plantejament, a la present Tesi ens hem proposat estudiar l'aplicació d'una tecnologia no tèrmica, com són les Altes Pressions Hidrostàtiques (HHP) per a l'obtenció d'un puré de kiwi segur, saludable (amb les seves propietats nutritives) i desitjable (sense perdre propietats organolèptiques). En la primera fase d'aquesta Tesi es van determinar les condicions de pressió, temperatura i temps del tractament HHP per reduir la seva càrrega microbiana endògena i estudiar l'evolució dels supervivents. A més es van inocular diferents indicadors de patògens, obtenint letalitats i capacitat de recuperació dels supervivents. A més a més, es van monitoritzar paràmetres que poguessin influir en la supervivència o creixement dels microorganismes, com pH, sòlids solubles, temperatures. En una segona fase, es van estudiar els paràmetres de qualitat fisicoquímica (color instrumental, degradació de les clorofil·les, reologia), nutritius (Vitamina C) i sensorials (panell de tastadors), en aquelles condicions que prèviament havien demostrat una seguretat microbiològica inicialment i al llarg del seu emmagatzematge. A mena de resum, destaquem els següents resultats obtinguts, respecte a la inactivació d'aerobis mesòfils (AM) totals es van observar reduccions de 2 i 3 Log a 300 MPa / 0.1 min i resta de condicions, respectivament. Els supervivents en els AM van ser esporulats (SP), ja que van coincidir amb els recomptes de supervivents. Però en cap cas hi va haver proliferació durant el seu emmagatzematge a 30 dies. Els microorganismes patògens inoculats (S. aureus i E. coli), van resultar ser molt més sensibles, ja que a partir de 500 MPa a qualsevol temps i temperatura assajades, no es observar supervivents, amb reduccions de 5 i 7 Log, respectivament. Les menors diferències de color entre les mostres pressuritzades enfront del control (ΔE) van ser les tractades a 10 °C, 5 minuts i 300 < 700 < 500 MPa. A més a més, el contingut de clorofil·les a i b, amb els tractaments de HHP assajats es va mantenir de l'ordre del 50-70% per a clorofil·la a i 60-80% per a clorofil·la b. Amb el tractament tèrmic de pasteurització aplicat només va quedat al 0 i 10% de clorofil·la a i b, respectivament. Per contra, la formació de feofitines (a i b) en les mostres tractades per HHP gairebé no va variar respecte al control, mentre que les mostres pasteuritzades van doblar el seu contingut. Es va poder observar que el contingut total de Vitamina C en les mostres tractades per HHP, tot just es va reduir respecte al seu control, durant el seu emmagatzematge. Només al dia 60, la diferència respecte al seu control va oscil·lar entre un 50-70% menor. A nivell d'anàlisi sensorial, els panelistes van distingir clarament les mostres tractades tèrmicament de les pressuritzades i control. Cal destacar que dels tractaments assajats, les mostres de 300 i 500 MPa a 15 min, van ser les que els panelistes van col·locar més pròximes al control Amb els resultats obtinguts en el present treball es demostra que els tractaments per HHP, són una alternativa per augmentar la vida útil del puré de kiwi, mantenint la seguretat microbiològica i unes característiques reològiques, organolèptiques i nutritives satisfactòries per als consumidors, com a mínim fins al dia 30 de conservació en refrigeració.
El consumo habitual de fruta (como el kiwi) en la dieta tiene un efecto muy beneficioso para la salud. No sólo es una excelente fuente de vitaminas, fibra y minerales, sino que además posee compuestos fitoquímicos que contribuyen a la salud. Por otro lado, los consumidores demandan cada día más de alimentos de preparación rápida, con una alta calidad nutritiva, sensorial y el mínimo de aditivos para su conservación. RESUMEN La primera impresión que los consumidores reciben de las frutas es la apariencia o aspecto externo, siendo la más importante para su aceptación y decisión de compra. La forma y tamaño son unos de los aspectos más fácilmente discernibles, aunque generalmente no es un carácter de calidad decisivo. Solo en caso de malformaciones o defectos morfológicos podría serlo. Durante y después de la cosecha del kiwi, un cierto porcentaje de la recolección no puede ser destinado a su distribución ya que no alcanza los estándares de comercialización. Por otro lado, existe un sector de población que precisa de facilidades a la hora de incentivar el consumo de frutas, y en concreto de kiwis, como son los niños, los ancianos y ciertos sectores para los cuales, por motivos de trabajo o prácticos, resulta un inconveniente el lavar, pelar y cortar ciertas frutas fuera de casa. En base a este planteamiento, en la presente Tesis nos hemos propuesto estudiar la aplicación de una tecnología no térmica, como son las Altas Presiones Hidrostáticas (HHP) para la obtención de un puré de kiwi seguro, saludable (con sus propiedades nutritivas) y apetecible (sin perder propiedades organolépticas). En la primera fase de esta Tesis se determinaron las condiciones de presión, temperatura y tiempos del tratamiento HHP para reducir su carga microbiana endógena y estudiar la evolución de los supervivientes. Además se inocularon diferentes indicadores de patógenos, obteniéndose sus letalidades y capacidad de recuperación de los supervivientes. A su vez, se monitorizaron parámetros que pudieran influenciar en la supervivencia o crecimiento de los microorganismos, como pH, sólidos solubles, temperaturas. En una segunda fase, se estudiaron los parámetros de calidad fisicoquímica (color instrumental, degradación de las clorofilas, reología), nutricional (vitamina C) y sensoriales (panel de catadores), en aquellas condiciones que previamente habían demostrado una seguridad microbiológica inicialmente y a lo largo de su almacenamiento. A modo de resumen, destacamos los siguientes resultados obtenidos, respecto a la inactivación de aerobios mesófilos (AM) totales se observaron reducciones de 2 y 3 Log a 300 MPa/0.1 min y resto de condiciones, respectivamente. Los supervivientes en los AM fueron esporulados (SP), ya que coinciden con los recuentos de supervivientes. Pero en ningún caso hubo proliferación durante su almacenamiento a 30 días. Los microorganismos patógenos inoculados (S. aureus y E. coli), resultaron ser mucho más sensibles, ya que a partir de 500 MPa a cualquier tiempo y temperatura ensayadas, no se observaros supervivientes, con reducciones de 5 y 7 Log, respectivamente. Las menores diferencias de color entre las muestras presurizadas frente al control (ΔE) fueron las tratadas a 10 °C, 5 min y 300 < 700 < 500 MPa. A su vez, el contenido de clorofilas a y b, con los tratamientos de HHP ensayados se mantuvo del orden del 50-70% para clorofila a y del 60-80% para clorofila b. Con el tratamiento térmico de pasteurización aplicado solamente quedó 0 y 10% de clorofila a y b, respectivamente. Por el contrario, la formación de feofitinas (a y b) en las muestras tratadas por HHP apenas varió respecto al control, mientras que las muestras pasteurizadas doblaron su contenido. Se pudo observar que el contenido total de Vitamina C en las muestras tratadas por HHP, apenas se redujo respecto a su control, durante su almacenamiento. Sólo al día 60, la diferencia con respecto a su control osciló entre un 50-70% menor. A nivel de análisis sensorial, los panelistas distinguieron claramente las muestras tratadas térmicamente de las presurizadas y control. Cabe resaltar que de los tratamientos ensayados, las muestras de 300 y 500 MPa a 15 min, fueron las que los panelistas colocaron más cercanas al control. Con los resultados obtenidos en el presente trabajo se demuestra que los tratamientos por HHP, son una alternativa para aumentar la vida útil del puré de kiwi, manteniendo la seguridad microbiológica y unas características reológicas, organolépticas y nutricionales satisfactorias para los consumidores, como mínimo hasta el día 30 de conservación en refrigeración.
Regular consumption of fruit (including kiwi) in the diet has a beneficial effect on health. It is not only an excellent source of vitamins, fiber and minerals, it also has phytochemicals that contribute to health. On the other hand, more and more consumers demand for fast food with high nutritional quality, sensory and minimum of additives for conservation. ABSTRACT The first impression consumers have from fruit it is the appearance or external aspect, being the most important for acceptance and purchase decision. The shape and size are among the most easily discernible aspects, but generally it is not a decisive quality character. Only if morphological abnormalities or defects could be a cause of reject. During and after kiwi harvest, a certain percentage of the harvest cannot be intended for distribution on not reaching marketing standards. On the other hand, there is a sector of the population that requires encourage for fruits consumption, specifically kiwis, such as children, the elderly and certain sectors whom for work or practical reasons, is a drawback to wash, peel and cut some fruits. Based on this approach, in this Thesis we intend to study the application of a non-thermal technology, such as high hydrostatic pressure (HHP), to obtain a kiwi puree safe, healthy (with its nutritional properties) and desirable (without losing organoleptic properties). In the first phase of this thesis the conditions of pressure, temperature and time of HHP treatment to reduce their endogenous microbial load and to study the evolution of the survivors were determined. Also, different indicators of pathogens were inoculated, obtaining their lethality rates and the resilience of the survivors. In turn, parameters that might influence the survival or growth of microorganisms such as pH, soluble solids, and temperature were monitored. In a second stage, physicochemical quality parameters (instrumental color, degradation of chlorophylls, rheology), nutritional (vitamin C) and sensory (taste panel), in the conditions that had previously shown a microbiological safety at the beginning and during storage, were studied. To summarize, we highlight the following results with respect to inactivation of aerobic mesophilic (AM) Total reductions Log 2 and 3 were observed at 300 MPa / 0.1 min and other conditions, respectively. The survivors were sporulated AM (SP), as they match survivors counts. In no case there was growth during storage at 30 days. For inoculated pathogenic microorganisms (S. aureus and E. coli), proved to be much more sensitive as from 500 MPa at any time and temperature tested, no survivors watch yourself, with reductions of 5 and 7 Log, respectively The lesser differences in color between pressurized samples versus control (ΔE) were treated at 10 °C, 5 min and 300 <700 <500 MPa. In turn, the content of pigment molecules with HHP treatments tested (300, 500 and 600 MPa and 0.1, 5 and 15 min) was maintained in the range 50-70% for chlorophyll a and 60-80% for chlorophyll b. With the pasteurization heat treatment remained just 0 and 10% for chlorophyll a and b, respectively. Conversely pheohytins formation in samples treated by HHP, hardly changed relative to the control, pasteurized samples doubled its contents. It was observed that the total content of Vitamin C in the samples treated by HHP, the gap narrowed just about control during storage, only at day 60 compared to control ranged between 50-70% lower. A level sensory testing, panelists clearly distinguished the samples heat treated and the pressurized control. It should be noted that the treatments tested, samples of 300 and 500 MPa for 15 min, were placed the closest to the control by panelists. With the results of this study demonstrated that treatment by HHP, are an alternative to increase the life of mashed kiwi, maintaining the microbiological safety and rheological, organoleptic and favorable to consumers nutritional characteristics, at least until the 30th day of storage.

Mestrado em Biotecnologia - Biotecnologia Alimentar
Este trabalho teve como objetivo o estudo da aplicação da tecnologia de Alta Pressão ao processo de produção do iogurte. Para isso, a fermentação foi realizada sob diferentes condições de pressão, utilizando iogurte natural como inóculo. A monitorização deste processo foi realizada recorrendo à análise de diversos parâmetros físico-químicos (acidez titulável, pH, concentração de açúcares redutores e outros mais específicos, como concentração de D-glucose, ácidos L- e D-láctico, acetaldeído e etanol). Também foi realizada uma análise microbiológica a Streptococcus thermophilus e Lactobacillus bulgaricus (bactérias fermentativas do inóculo utilizado) de modo a inferir a sua viabilidade durante as fermentações testadas. Pela análise físico-química, conclui-se que o aumento da pressão influencia negativamente a velocidade fermentativa, sendo que sob 100 MPa o processo fermentativo é completamente inibido. Foi também realizada uma análise cinética, onde foi verificado que a acidez titulável era o parâmetro menos afetado pelo aumento da pressão. Adicionalmente, foram realizadas fermentações à pressão atmosférica com pré-tratamentos variáveis de pressão (50 MPa ou 100 MPa durante 90 ou 180 minutos). Em todos os pré-tratamentos testados não houve fermentação, mas depois, a fermentação começa à pressão atmosférica, sendo que a sua velocidade depende das condições do pré-tratamento utilizado (pressão/tempo). No pré-tratamento de 100 MPa durante 90 minutos houve um aumento considerável da velocidade fermentativa, sendo mais rápida que a fermentação sem pré-tratamento, enquanto que com um pré-tratamento mais longo, a velocidade fermentativa diminui. Pela análise da concentração de D-glucose, verifica-se que quando não há fermentação, há uma maior concentração de D-glucose no meio, o que pode ser explicado pela hidrólise da lactose presente no leite. A concentração dos dois isómeros de ácido láctico está de acordo com os resultados obtidos para a acidez titulável (aumenta com o tempo de fermentação), e adicionalmente verifica-se que no iogurte, o isómero L- está em maior quantidade do que o isómero D-. O acetaldeído está presente numa baixa concentração no iogurte e a sua produção também é inibida com o aumento da pressão, tal como acontece com outros produtos da fermentação. Quanto ao etanol, não foi possível quantificar pelo método utilizado. Com a análise microbiológica realizada verificou-se que o aumento da pressão inibe o crescimento das bactérias fermentativas. Para além disso, verificou-se que S. thermophilus é mais resistente à pressão do que L. bulgaricus e está presente em maiores quantidades no iogurte.
The purpose of this work was the study of high pressure technology application on set yogurt’s production process. For that, the fermentation process was performed under different pressure conditions, using set yogurt as inoculum. In order to monitor product formation and substrate consumption over the fermentation time, analyses were performed for several physicochemical parameters (titratable acidity, pH variation, reducing sugars concentration and parameters more specific as D-glucose, L- and D-lactic acids, acetaldehyde and ethanol concentrations). A microbiological analysis to Streptococcus thermophilus and Lactobacillus bulgaricus (starter cultures of set yogurt) was also performed in order to evaluate its viability during fermentation under the pressure conditions tested. By analyzing general physicochemical parameters, it was possible to conclude that increasing fermentation pressure influences negatively the fermentation rate and with pressures around 100 MPa, the fermentative process was totally inhibited. Through a kinetic analysis, it was verified that titratable acidity was the parameter lesser affected by increasing fermentation pressure. In addition, fermentation at atmospheric pressure with variable pressure pre-treatments (50 or 100 MPa for 90 or 180 minutes) was performed. In all pre-treatments tested in this work, there was no fermentation during pre-treatment, but at atmospheric pressure the fermentation occurs and its rate depends of pre-treatment conditions (pressure and time). With a pre-treatment of 100 MPa for 90 minutes there has a significant increase of fermentative rate, became faster than fermentation without pre-treatment, but when the pre-treatment time increases, the fermentation rate also increases. With D-glucose concentration analysis, it was verified that when fermentation stops, D-glucose concentration increases, which can be explained by milk’s lactose hydrolysis. Lactic acid isomers concentration are in accordance to titratable acidity results obtained (increasing over fermentation time) and it was verified that L-lactic acid is present in higher amount than D- isomer. Acetaldehyde was present in small amounts in yogurt and its production was inhibited with the increasing pressure, as the others fermentation products analyzed. In what regards to ethanol production, it was not possible to quantify by the analytical method applied. The microbiological analysis indicated that increasing pressure inhibits starters’ growth. S. thermophilus was more resistant to pressure than L. bulgaricus and the former one was present in a higher amount in yogurt.

Mestrado em Ecologia Aplicada
Recentemente têm sido identificados alguns perigos relativamente ao ambiente no mar profundo, como atividades de mineração marinha, e que exigem uma melhor compreensão sobre as características únicas destes ecossistemas. A alta pressão hidrostática (HHP) é uma das condições abióticas mais importantes para a vida neste ambiente; no entanto os seus efeitos nos processos e estruturas dos organismos são pouco compreendidos. Enquanto a realização de testes com organismos do fundo do mar é muito desafiadora e cara, avaliar os efeitos da HHP utilizando espécies de águas rasas parece ser a melhor abordagem. O camarão Palaemon varians é uma espécie com estreita relação filogenética com algumas espécies-chave do mar profundo. No presente estudo, P. varians foi exposto a uma gama de diferentes HHP (10, 20, 30 e 40 MPa) e a duas temperaturas diferentes (4 ºC e 20 ºC), e diversos marcadores bioquímicos (as actividades de AChE, GST e CAT e os níveis de LPO) foram medidos a fim de avaliar a utilização desta espécie como modelo para estudos a desenvolver em laboratório. Todos os animais expostos a HHP acima de 20 MPa morreram durante a exposição. Embora nenhuma interação nos marcadores bioquímicos medidos tenha sido encontrada entre HHP e temperatura, os animais expostos a 20 MPa e 4 ° C também morreram durante a exposição. Os níveis de LPO e a atividade da GST aumentaram a temperaturas baixas, e por isso a utilização desta espécie a essas temperaturas requer uma investigação mais aprofundada. Devido à ausência de resposta de todos os biomarcadores medidos, esta espécie parece ser adequado para ensaios laboratoriais com pressões de 10 MPa. A pressões de 20 MPa, foram observadas algumas alteração nos níveis de LPO e AChE após 8 horas de recuperação da exposição sendo por isso necessário aprofundar o estudo destes efeitos. Além disso, a mortalidade registada a temperaturas baixas faz com que o uso desta espécie em tais pressões seja limitada. Na segunda parte deste trabalho, a fim de avaliar o efeito da pressão sobre a sensibilidade desta espécie para a exposição a cádmio, P. varians foi exposto a várias concentrações de cádmio durante 96 h, juntamente com diferentes regimes de pressão: pressão atmosférica; simultaneamente, durante 8 horas, com uma pressão de 20 MPa; e pré-expostos a 20 MPa durante 8 h. Os valores de LC50 calculados foram semelhantes para os diferentes regimes de pressão, o que indica que a esta pressão não são observados efeitos sobre a toxicidade do cádmio para P. varians. Embora esta seja uma avaliação importante dos efeitos tóxicos do cádmio a pressões elevadas, são necessários estudos adicionais sobre outras espécies e outros produtos químicos que também são propensos a aparecer no fundo do mar.
The recent rising threats to the deep-sea, as deep-sea mining, require a better understanding about the unique characteristics of these ecosystems. High hydrostatic pressure (HHP) is one of the most important abiotic conditions to life in this environment; however its effects on processes and structures of the organisms are very poorly understood. While experimentation with organisms from the deep-sea is very challenging and expensive, assessing the effects of HHP using shallow-water species seem to be best approach. The caridean shrimp Palaemon varians is a species with close phylogenetic relation with some key species in the deep-sea. In the present study, P. varians was exposed to a range of different HHP (10, 20, 30 and 40 MPa) and to two different temperatures (4 ºC and 20 ºC), and biochemical markers (AChE, GST, CAT activities and LPO level) were measured in order to evaluate the use of this species as a model for future laboratory research. All animals died during exposure at HHP above 20 MPa. While no interaction between HHP and temperature on biochemical markers were found, animals at 20 MPa and 4 ºC also died during the exposure. LPO levels and GST activity increased at low temperatures, and the use of this species at such temperatures requires further investigation. Due to the absence of response of all biomarkers measured, this species seems to be suitable for laboratory assays with pressures of 10 MPa. At 20 MPa, some small alteration in LPO and AChE levels after 8 hours post exposure may require further investigation. Also, the mortality registered at low temperatures makes the use of this species at such pressures limited. In order to evaluate the effect of pressure on the sensitivity of this species to cadmium, P. varians were exposed to several concentration of cadmium during 96h, along with different pressure regimes: at atmospheric pressure; simultaneously, for 8h, with a pressure of 20 MPa; and pre-exposed to 20 MPa for 8 h. Only slightly differences were found between the calculated LC50 for the different pressure regimes, indicating that at this pressure no effects on the toxicity of cadmium to P. varians are observed. Although this is an important input regarding hazard assessment at higher pressures, additional studies are needed regarding other species and other chemicals that are also prone to appear in the deep sea.

In this thesis we have used temperature and high pressure to investigate the loss mechanisms present in visible, near infrared and infrared strained and unstrained semiconductor lasers. We find that tensile strained lasers show pressure dependent loss mechanisms similar in magnitude to those of unstrained and compressively strained devices. We present for the first time measurements of the temperature sensitivity of long wavelength lasers as a function of high pressure. Unstrained lasers show a pressure dependent temperature sensitivity whilst tensile strained lasers do not, over the range 150K to 300K. This leads us to conclude that phonon assisted Auger may be more significant than band to band Auger in tensile strained devices. We also demonstrate a possible mechanism for the decrease of Auger for these quantum well structures by estimating the effect of pressure on the gain - carrier density relation. High pressure measurements on 800nm GaAs quantum well lasers with superlattice barriers show the effect of changing the relative positions of the superlattice barrier IF and X minima. We find that the threshold current increases rapidly when the barrier is made indirect and conclude that this effect is due to repopulation of the barrier X minima with electrons from the active quantum well. For visible lasers we find that above lOkbar the effect of pressure on the threshold current is an increase which is attributable to losses from the active region to the X minima in the barrier. For a Philips bulk visible laser the threshold current remains relatively constant with pressure below lOkbar, whereas a Philips compressively strained device shows a decrease in Iý of about 25% up to 6kbar, a behaviour never seen before in short wavelength lasers. For the Philips 1% compressively strained laser the increase in Ith above 6kbar is also attributed to losses to the X minima. Measurements of a 1% compressively strained IBM laser showed immediate increases of threshold current with pressure, which is again attributed to the X minima in the barriers.

This study was motivated by a theoretical formulation on mechanobiology of soft and hard skeletal tissue differentiation. To prove this formulation experimentally, I hypothesized that cartilaginous phenotype can be induced in vitro in a seemingly non-cartilaginous cell source from fibrous tissue. In testing this hypothesis, I have focused on cartilage as a target and fibrous tissue as an origin or the source of cell. Four different trials were pursued with one supposition in common, i.e. hydrostatic pressure is one of the main driving forces for chondroinduction in vitro. The first and second trials pertained to the influence of a relatively short and long duration cyclic hydrostatic compression on rat Achilles tendon fibroblasts. The third trial was to examine the effect of two different drugs on cytoskeletal elements of mesenchymal stem cells or mouse embryonic fibroblast lines in pellet cultures combined with the similar duration and/or frequency of cyclic hydrostatic pressure adopted in the aforesaid trials with no pharmacological agents added. Last, attempts were made to implement an advanced technique in molecular biology called 'PCR array' to further quantify expression levels of eighty four pathway-specific genes in mouse TGFbeta/BMP signaling traffic under the same physiological regimen of hydrostatic compression. Results demonstrated that transdifferentation in phenotype from tendon to fibrocartilage may have occurred in vitro in tendon fibroblasts in pellet cultures exposed to hydrostatic pressure. Experiments on the role of the cytoskeleton in mechanotransduction of the applied level of hydrostatic pressure demonstrated that disruption of microfilaments in the presence of cytochalasin-D did not significantly interfere with the anabolic effect of cyclic pressure. However, disruption of microtubule assembly by nocodazole abolished the pressure-induced stimulation in cartilage marker genes. These findings suggest that microtubules, but not microfilaments, are involved in mechanotransduction of hydrostatic pressure by mesenchymal stem cells.

Accelerated Life Testing (ALT) is an effective method of demonstrating and improving product reliability in applications where the products are expected to perform for a long period of time. ALT accelerates a given failure mode by testing at amplified stress level(s) in excess of operational limits. Statistical analysis (parameter estimation) is then performed on the data, based on an acceleration model to make life predictions at use level. The acceleration model thus forms the basis of accelerated life testing methodology. Well established accelerated models such as the Arrhenius model and the Inverse Power Law (IPL) model exist for key stresses such as temperature and voltage. But there are other stresses like subsea pressure, where there is no clear model of choice. This research proposes a pressure-life (acceleration) model for the first time for life prediction under subsea pressure for key mechanical/physical failure mechanisms. Three independent accelerated tests were conducted and their results analyzed to identify the best model for the pressure-life relationship. The testing included material tests in standard coupons to investigate the effect of subsea pressure on key physical, mechanical, and electrical properties. Tests were also conducted at the component level on critical components that function as a pressure barrier. By comparing the likelihood values of multiple reasonable candidate models for the individual tests, the exponential model was identified as a good model for the pressure-life relationship. In addition to consistently providing good fit among the three tests, the exponential model was also consistent with field data (validation with over 10 years of field data) and demonstrated several characteristics that enable robust life predictions in a variety of scenarios.; In addition the research also used the process of Bayesian analysis to incorporate prior information from field and test data to bolster the results and increase the confidence in the predictions from the proposed model.
ID: 029051131; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2010.; Includes bibliographical references (p. 165-173).
Ph.D.
Doctorate
Department of Industrial Engineering and Management Systems
Engineering and Computer Science

The collapse-behaviour of pipes was to be studied by use of Finite Element modelling.Existing analytical expressions for collapse were evaluated and especially the one used inDNV-OS-F101 was decided to be studied in comparison with FE-model results.Parameters that may influence the collapse capacity and are not included in the analyticalexpressions –flattening, peaking, eccentricity, local wall thickness variation, materialstress-strain curve, residual stresses - were defined and explained. A model was built inthe Finite Element software package Abaqus v6.9.1 and several articles on collapsetesting used to verify it. The aforementioned parameters were studied by use ofsensitivity studies and the results shown and discussed. Effective thickness definitions foruse in the DNV-formula and the DNV-yield stress criterion were discussed in the contextof the results. The results seemed to indicate that the transition between the elastic andplastic range of the material stress-strain curve was of great importance. The results werediscussed in the context of the different collapse-related parameters defined beforehandand some concluding remarks were made on possible further work related to thesefindings.

Hydrostatic Pressure Machines (HPM), are a class of hydropower energy converter designed to operate at sites with heads below 3 meters; sites receiving increasing interest as the demand for power from renewable energy sources grows. The HPM is a ‘Pressure machine’, applying the pressure produced by differing water levels at a site, directly to the blades of the device to extract power. Prior to the current research, these machines had only existing as laboratory models. This thesis describes the design, construction and testing of a 5 kW prototype HPM installed at a re-activated mill site in Bavaria. Observations and performance test results from this full scale unit are then compared with the results of scale model tests carried out in the laboratory. New theory is developed to account for the geometry of the prototype machine and the variations in water levels encountered during operation. This is found to give very good agreement with performance measurements from both prototype and model tests, with no scale effects identified between the scales over the normal operating range of the machine. Several alternative rotor designs are tested at model scale, which demonstrate useful performance gains compared with the prototype machine. Direct blade force and cell pressure measurements are also obtained during model operation which has increased our understanding of the energy exchanges taking place between rotor and fluid within the machine. This in turn helps to identify the key machine geometries which impact performance.

Adaption to environmental stresses is vital for the survival of all organisms living in any environment. Two of the major environmental factors in the deep sea environment are high hydrostatic pressure and high salt concentration. Hydrostatic pressure and osmotic pressure share similarities in their effects on organisms living in the deep sea but this overlap has been little explored. Major studies from Japan and California over the last 40 years have shown the effects of hydrostatic pressure on bacteria from the deep sea (see [1] for a review). These are complemented by work by Yancey et al. [2] showing that specific solutes accumulated in response to osmotic pressure in fish have the ability to enhance resistance to hydrostatic pressure. However, this work has been done in vitro or with larger organisms and not much is known about the overlap of osmotic and hydrostatic pressure in bacteria. In this study I investigated the effects of osmotic and hydrostatic pressure on two model organisms: Photobacterium profundum and Escherichia coli. In order to accomplish this task I developed novel imaging equipment which allows for high resolution imaging of bacteria at pressure. I also developed a new method of growing bacteria in 96-well plates at high pressure, which lead to the identification of a hierarchy of genes essential for the growth of E. coli at pressure. I used the same 96-well plate technique to monitor the growth of P. profundum at differing osmotic and hydrostatic pressures. Furthermore I also attempted to analyse the solutes accumulated by different strains of P. profundum in response to osmotic and hydrostatic pressures.

Hydrostatic transmission is used in many applications where high torque at low speed is demanded. For this project a forest vehicle is at focus. Komatsu Forest would like to have a model for the pressure in the hose between the hydraulic pump and the hydraulic motor. Pressure peaks can arise when the vehicle changes speed or hit a bump in the road, but if a good model is achieved some control action can be developed to reduce the pressure peaks.

For simulation purposes a model has been developed in Matlab-Simulink. The aim has been to get the simulated values to agree as well as possible with the measured values of the pressure and also for the rotations of the pump and the motor.

The greatest challenge has been due to the fact that the pressure is a sum of two flows, if one of these simulated flows is too big the pressure will tend to plus or minus infinity. Therefore it is necessary to develop models for the rotations of the pump and the motor that stabilize the simulated pressure.

Different kinds of models and methods have been tested to achieve the present model. Physical modeling together with a black box model are used. The black box model is used to estimate the torque from the diesel engine. The probable torque from the ground has been calculated. With this setup the simulated and measured values for the pressure agrees well, but the fit for the rotations are not as good.

La mesure de pression est un domaine vieux de plusieurs siècles, dont le développement a été motivé par l’importance de ses applications technologiques. Le but de ce travail est de proposer une technique de mesure de fortes pression hydrostatiques par capteur optique à bas coût. De nombreux types de capteurs de pression ont été développés au cours du temps, et la première partie de ce document présente une vue d’ensemble du domaine. Nous nous concentrons ensuite sur les techniques optiques et présentons leurs avantages et inconvénients. Au vu de notre cahier des charges, nous choisissons de développer un capteur de pression basé sur l’effet piezo-optique, c’est à dire l’apparition d’une biréfringence dans un matériau diélectrique soumis à une force extérieure. La Partie II du mémoire présente les différents outils qui seront par la suite utilisés pour modéliser le capteur proposé : tout d’abord nous rappelons les détails de la théorie de la polarisation, son origine physique ainsi que le formalisme de Mueller-Stokes. Nous nous intéressons ensuite aux interactions entre une lumière polarisée et un milieu diélectrique, en présentant l’effet piezo-optique ainsi que les effets polarisant des réflexions à une interface. Les effets présentés sont modélisés par leur matrice de Mueller afin de simplifier l’étude à suivre. Dans la Partie III nous proposons un concept original de capteur de pression, utilisant une approche novatrice par rapport à celle usuellement mise en œuvre. Le capteur proposé est basé sur l’analyse d’une lumière dont la polarisation est modifiée par la traversée d’un milieu diélectrique rendu biréfringent par la pression à mesurer. Certains aspects du capteur sont optimisés, et ses inconvénients discutés. Cette étude aboutit à la proposition d’un capteur dans lequel les éléments polarisant discrets ont été remplacés par des réflexions successives. Ce nouveau concept est modélisé, puis nous présentons les différentes sources potentielles d’erreur de mesure et proposons des solutions pour compenser celles qui prédominent. La Partie IV présente la validation expérimentale des concepts précédents. Nous décrivons la conception, la calibration et la validation d’un polarimètre de Mueller par Transformée de Fourier, conçu dans le but d’étudier la dépendance de l’effet piezo-optique à la température. Ensuite nous présentons la réalisation d’un démonstrateur de capteur piezo-optique de pression. Les essais effectués sont en accord avec les prédictions théoriques et valident donc le principe du capteur développé au cours de ce travail
The measurement of pressure is a field that has been studied for centuries due to its important technological implications. Our goal is to propose an original method to measure high hydrostatic pressures using a low cost optical sensor. A number of pressure sensors have been developed over the years, and the first part of this work presents an overview of the main ones. We then focus on optical pressure sensors, discuss the advantages and inconveniences of each method with regards to our constraints, and decide to develop the concept of a sensor based on the piezo-optic effect, i. E. The stress-induced birefringence in a transparent dielectric subjected to a force. We presents the tools that will be used to modelize the piezo-optic pressure sensor: we first review the theory of polarization of light, from its physical origin to the Mueller-Stokes formalism; we then focus on the interaction of polarized light with matter: we discuss the theory of the piezooptic effect and the polarization effects of total and partial reflections at an interface. Both effects are modelized in terms of their Mueller matrices. We then propose an original concept for a pressure sensor, using an approach different from the one usually seen in polarimetric sensors. First the concept of a piezo-optic pressure sensor is presented where polarized light interacts with a dielectric material subjected to a pressure; the resulting state of polarization is analyzed by a second polarizer and a photodetector. Some aspects of the sensor are optimized while its shortcomings are listed. In light of this analysis we propose a revised concept to addresses these issues. The new proposal uses carefully oriented reflections to replace all polarizing elements, enabling simpler and cheaper production. We modelize this device, analyze its optical behavior, and then present the different sources of measurement error. Most of them are negligible, and we present methods to mitigate the influence of these that are not. Part IV focuses on the experimental validation of the concepts presented so far. We describe the conception, calibration and validation of a Fourier Transform Mueller polarimeter that we intend to use to study the temperature dependence of the piezo-optic effect. We build a prototype based on the initial concept of the piezo-optic pressure sensor presented in Part III, and test its response to pressure. Its behaviour is found to be coherent with theoretical predictions, and these measurement serve to validate the concept of the sensor that was developed during this work

The normal depth usage of the juvenile lemon shark, Negaprion brevirostris was determined using data storage tags which logged pressure and temperature.  Sharks were found to predominantly occupy water depths between the surface and 1m.  A diel rhythm and a tidal rhythm were found for the pressure data.  Simultaneous acoustic tracking showed shallow water use despite the availability of deeper areas within the sharks’ home ranges.  All sharks mainly occupied a narrow range of temperatures (29°C - 31°C) at the high end of their range.  Temperature data showed mainly diel rhythms with slight tidal influence.  Pressures and temperatures used by the sharks seemed to be affected by size of home range, individual preference and predator avoidance.  The behaviour of the lesser spotted dogfish Scyliorhinus canicula was investigated during controlled small steps of pressure inside a hypobaric chamber.  Swimming occurred in response to decreasing pressure with increased swimming speed and duration suggesting enhanced sensitivity of the shark pressure sensor within  a narrow range between 39mbar above and down to 195mbar below barometric pressure.  Further studies using a novel tidal tank system showed that Scyliorhinus synchronised their activity with a 12.5 hour tidal cycle but not with a 9  hour cycle.  When different resting depths were made available, they were utilised by dogfish, suggesting an individual preference independent of environmental cues or the presence of the opposite sex.  Isolated vestibular systems were challenged over a range of pressures. Hair cell afferent activity showed responses to sinuosoidal cycles and step changes of pressure.  Temperature effects are complex but were small compared with pressure effects.  Knowledge of the pressure sensor and vertical range used by sharks is essential in the present development of marine protected areas in an attempt to ultimately aid the conservation of sharks.

The effects of mechanical forces on endothelial cell function and behavior are well documented, but have not been fully characterized. Specifically, fluid pressure has been shown to elicit physical and chemical responses known to be involved in the initiation and progression of endothelial cell-mediated vascularization. Central to the process of vascularization is the formation of tube-like structures. This process—tubulogenesis—is essential to both the physiological and pathological growth of tissues. Given the known effects of pressure on endothelial cells and its ubiquitous presence in the vasculature, we investigated pressure as a magnitude-dependent parameter for the regulation of endothelial tubulogenic activity. To accomplish this, we exposed two- and three-dimensional bovine aortic endothelial cell (BAEC) cultures to static pressures of 0, 20, and 40 mmHg for 3 and 4 days. The most significant findings were: (1) cells in two-dimensional culture exposed to 20, but not 40, mmHg exhibited significantly (p < 0.05) increased expression of both VEGF-C and VEGFR-3, and (2) cells in three-dimensional culture exposed to 20, but not 40, mmHg exhibited significant (p > 0.05) increases in endothelial sprouting. These findings evidence the utility of pressure as a selective modulator of tissue microvascularization in vitro and implicates pressure as factor in pathological tubulogenesis in vivo.

Afferent activity, from the statocyst thread hairs of Carcinus maenas (L.), was altered by micro-pressure stimulation. Recordings showed that thread hair responses lag peak pressuring during low (1 kPa) pressure stimulation, but that response gain was maximal during such pressures. Increasing amplitude and decreasing cycle period reduced both lag and response gain. Data suggest a role for the thread hair in determining pressures and rates of pressure change of tidal periodicity. All available data were compatible with a transduction mechanism differentially activating paired bipolar neurones to a pressure increase. During angular acceleration evoked responses, post stimulus time histograms revealed an increased phase lag (re peak acceleration) with increasing pressure. Abrupt increases in directional class of unit responding to oscillation appeared at between 5-15 kPa. Comparative experiments, using the portunid crabs Necora puber (L.) and Liocarcinus depurator (L.) found that responses to rapid rates of pressure change were significant. No such responses were found in Carcinus maenas. Interneurone recordings were composed of abrupt elevations in spike frequencies followed by quiescent periods. In freshly caught animals, burst duration does not differ significantly throughout the tidal period. The quiescent period (interburst interval) was significantly longer at periods of expected low tide. Recordings made during pressure cycling show periodicities similar to that of the imposed pressure cycle. Applying 30 minute period, 30 kPa hydrostatic pressure cycles to loosely tethered crabs reduced burst duration significantly. Interburst interval increases significantly during pressure application. At cycle periods greater than 120 minutes, interburst intervals and burst durations were not significantly affected. At longer cycle periods (between 3-12 hrs) there were spike frequency and distributions of activity cycles comparable to those found in freshly caught, free-walking crabs. Preliminary results from recordings of statocyst afferents in the mysid Praunus flexuosus (Müller) show graded responses to micro-pressure stimulation.

Thesis (M.S. in Engineering Acoustics)--Naval Postgraduate School, March 2004.
Thesis advisor(s): Thomas R. Howarth, Dehua Huang. Includes bibliographical references (p. 67-69). Also available online.

This thesis describes an experimental investigation of the photoluminescence emissions from firstly, bulk In0.53 Ga0.47 As and secondly, InGaAs\InP and AlAs\GaAs quantum well structures, as a function of hydrostatic pressure. Two high pressure systems have been developed and successfully used in the course of this work, an 8kbar piston and cylinder system and a miniature diamond anvil cell. From the high pressure measurements on the bulk InGaAs, both at room anti liquid nitrogen temperatures, it is shown that the pressure dependence of the direct band-edge luminescence is non-linear and independent of temperature. Using an empirical equation of state and making some assumptions as to the value of the bulk modulus, it is found that the band-edge luminescence is linearly dependent upon the lattice constant and may be described by a band-edge deformation potential of -8.25 +/- 0.1eV. Theory compares favourably with this value. From low temperature measurements of both quantum well systems it has been possible to deduce a quantitative description of how the conduction and valence band-edge discontinuities vary as a function of the applied pressure. It is shown that the band-offset ratio changes with pressure. This work constitutes the first observation of this phenomenon which had previously been thought either too small to be of consequence, or simply ignored. It is found that the conduction-band discontinuity in InGaAs\InP quantum wells decreases at -2.3 +/- 0.6meV/kbar while its valence-band discontinuity remains constant. The valence-band discontinuity in the AlAs\GaAs superlattice is directly measured to increase at +1.1 +/- 0. ImeV/kbar. An analysis of reported data for A1 Ga As/GaAs quantum wells shows that the pressure coefficient of the X l-x valence-band discontinuity is linearly dependent upon the alloy composition x. Theories of band-offset ratios and in particular the "model-solid" theory of Van de Walle and Martin (Van de Walle 1987), agree exceedingly well with these experimental findings. It is suggested that such agreement lends weight to the assumption that heterojunction band-edge discontinuities are intrinsic to the bulk properties of the host materials.

This research examines the role of actin cytoskeleton filaments in chondroinduction by cyclic hydrostatic pressurization. A chondroinductive hydrostatic pressurization system was developed and characterized. A pressure of 5 MPa at 1 Hz frequency, applied for 7200 cycles (4 hours intermittent) per day, induced chondrogenic differentiation in C3H10T1/2 cells while 1800 cycles (1 hour intermittent) did not induce chondrogenesis. Quantitative analysis of chondrogenesis was determined as sulfated glycosaminoglycan synthesis and rate of collagen synthesis while qualitative analysis was obtained as Alcian Blue staining and collagen type II immunostaining. Actin disruption using 2 uM Cytochalasin D inhibited the enhanced sGAG synthesis in the chondroinductive hydrostatic pressurization environment and significantly inhibited rate of collagen synthesis to the mean level lower than that of the non-pressurized group. These results suggest an involvement of actin cytoskeleton filaments in mechanotransduction of cyclic hydrostatic pressure.

Fresh and fresh-cut tomatoes have been associated with numerous outbreaks of salmonellosis in recent years. While the exact routes of contamination are unknown, high pressure processing (HPP) is being evaluated as a post harvest treatment to eliminate Salmonella enterica from tomatoes. The objectives of the study were to determine the potential for of HPP to reduce S. enterica serovars Newport, Javiana, Braenderup and Anatum (clinical isolates from tomato outbreaks) in tryptic soy broth (TSB) and to determine the effect of HPP to reduce the most pressure resistant S. enterica serovar from fresh diced and whole tomatoes. Five ml portions of broth containing 8 log CFU/ml of one of the four serovars (nalidixic acid resistant) were packaged in sterile stomacher bags and subjected to one of three different pressures (350, 450, or 550 MPa) for 120s. Samples were enumerated by surface plating onto tryptic soy agar supplemented with 50 ppm nalidixic acid (TSAN) and incubated at 35°C for 48 hours. The most pressure resistant S. enterica serovar evaluated was Braenderup. Subjecting the broth culture to 350, 450 and 550 MPa resulted in a 4.53, 5.74 and 7.09 log reduction in S. Braenderup, respectively. Diced tomatoes (150g) and whole red round tomatoes (150g; packaged in 350ml of 1% CaCl2) were inoculated with S. Braenderup, to obtain 6 log CFU/g throughout the sample and subjected to the same pressure treatments as described above. After HPP, diced tomatoes were homogenized for 1 minute and then plated on TSAN. Whole tomatoes were surface sampled, and then homogenized for 1 minute. Surface and homogenate samples were plated on TSAN supplemented with 1% pyruvic acid (TSANP). Significant reductions of S. Braenderup concentrations in diced tomatoes (P < 0.05) were seen after processing at 350 (0.46 CFU/g), 450 (1.44 log CFU/g), and 550 MPa (3.67 log CFU/g). In whole tomatoes, significant reductions (P < 0.05) were also seen at 350 (1.41 log CFU/g), 450 (2.25 log CFU/g) and 550 MPa (3.35 log CFU/g). There were no differences in visual appearance between fresh and HPP diced and whole tomatoes. HPP may be an effective post harvest strategy to reduce low levels of S. enterica contamination in diced tomatoes.
Master of Science in Life Sciences

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.
Includes bibliographical references (leaves 51-54).
An important part of a routine clinical examination is the assessment of the arterial blood pressure waveform. The variations in shape of the waveform indicate the presence of disease. In this work, a method is developed for the reconstruction of arterial blood pressure waveform using the signals obtained from a noninvasive wearable photoplethysmographic Ring Sensor and hydrostatic pressure variations measured by an Arm Accelerometer Sensor. A dynamic model with the Wiener model structure is used to establish the relationship between transmural pressure and photoplethysmographic signal. Tuned nonlinear dynamic model has been shown to be capable of estimating the arterial blood pressure waveform. The algorithm has been applied to experimental blood pressure measurements in a healthy subject and shown to provide accurate waveform reconstruction. As a result, the use of a wearable photoplethysmographic Ring Sensor can be extended to provide a finger arterial blood pressure waveform.
by Aleksandar Marinković.
S.M.