27 resultados para K Current
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A thermal Energy Storage Unit (ESU) could be used to attenuate inherent temperature fluctuations of a cold finger, either from a cryocooler working or due to sudden income heat bursts. An ESU directly coupled to the cold source acts as a thermal buffer temporarily increasing its cooling capacity and providing a better thermal stability of the cold finger (Power Booster mode). The energy storage units presented here use an enthalpy reservoir based on the high latent heat of the liquid-vapour transition of neon in the temperature range 38 - 44 K to store up to 900 J, and that uses a 6 liters expansion volume at RT in order to work as a closed system. Experimental results in the power booster mode will be described: in this case, the liquid neon cell was directly coupled to the cold finger of the working cryocooler, its volume (12 cm3) allowing it to store 450 J at around 40 K. 10 W heat bursts were applied, leading to liquid evaporation, with quite reduced temperature changes. The liquid neon reservoir can also work as a temporary cold source to be used after stopping the cryocooler, allowing for a vibration-free environment. In this case the enthalpy reservoir implemented (24 cm3) was linked to the cryocooler cold finger through a gas gap heat switch for thermal coupling/decoupling of the cold finger. We will show that, by controlling the enthalpy reservoirs pressure, 900 J can be stored at a constant temperature of 40 K as in a triple-point ESU.
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Cryocoolers have been progressively replacing the use of the stored cryogens in cryogenic chains used for detector cooling, thanks to their higher and higher reliability. However, the mechanical vibrations, the electromagnetic interferences and the temperature fluctuations inherent to their functioning could reduce the sensors sensitivity. In order to minimize this problem, compact thermal energy storage units (ESU) are studied, devices able to store thermal energy without significant temperature increase. These devices can be used as a temporary cold source making it possible to turn the cryocooler OFF providing a proper environment for the sensor. A heat switch is responsible for the thermal decoupling of the ESU from the cryocoolers temperature that increases when turned OFF. In this work, several prototypes working around 40 K were designed, built and characterized. They consist in a low temperature cell that contains the liquid neon connected to an expansion volume at room temperature for gas storage during the liquid evaporation phase. To turn this system insensitive to the gravity direction, the liquid is retained in the low temperature cell by capillary effect in a porous material. Thanks to pressure regulation of the liquid neon bath, 900 J were stored at 40K. The higher latent heat of the liquid and the inexistence of triple point transitions at 40 K turn the pressure control during the evaporation a versatile and compact alternative to an ESU working at the triple point transitions. A quite compact second prototype ESU directly connected to the cryocooler cold finger was tested as a temperature stabilizer. This device was able to stabilize the cryocooler temperature (( 40K 1 K) despite sudden heat bursts corresponding to twice the cooling power of the cryocooler. This thesis describes the construction of these devices as well as the tests performed. It is also shown that the thermal model developed to predict the thermal behaviour of these devices, implemented as a software,describes quite well the experimental results. Solutions to improve these devices are also proposed.
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Cryocoolers have been progressively replacing the use of the stored cryogens in cryogenic chains used for detector cooling, thanks to their higher and higher reliability. However, the mechanical vibrations, the electromagnetic interferences and the temperature fluctuations inherent to their functioning could reduce the sensors sensitivity. In order to minimize this problem, compact thermal energy storage units (ESU) are studied, devices able to store thermal energy without significant temperature increase. These devices can be used as a temporary cold source making it possible to turn the cryocooler OFF providing a proper environment for the sensor. A heat switch is responsible for the thermal decoupling of the ESU from the cryocoolers temperature that increases when turned OFF. In this work, several prototypes working around 40 K were designed, built and characterized. They consist in a low temperature cell that contains the liquid neon connected to an expansion volume at room temperature for gas storage during the liquid evaporation phase. To turn this system insensitive to the gravity direction, the liquid is retained in the low temperature cell by capillary effect in a porous material. Thanks to pressure regulation of the liquid neon bath, 900 J were stored at 40K. The higher latent heat of the liquid and the inexistence of triple point transitions at 40 K turn the pressure control during the evaporation a versatile and compact alternative to an ESU working at the triple point transitions. A quite compact second prototype ESU directly connected to the cryocooler cold finger was tested as a temperature stabilizer. This device was able to stabilize the cryocooler temperature (( 40K 1 K) despite sudden heat bursts corresponding to twice the cooling power of the cryocooler. This thesis describes the construction of these devices as well as the tests performed. It is also shown that the thermal model developed to predict the thermal behaviour of these devices,implemented as a software, describes quite well the experimental results. Solutions to improve these devices are also proposed.
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Direct Research Internship Course
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NSBE - UNL
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RESUMO: Na descrio deste estudo foi utilizada a terminologia anatmica da Sociedade Brasileira de Anatomia adaptada ao portugus por J. A. Esperana-Pina de acordo com o tratado Anatomia Humana da Relao. Os actuais estudos sobre hipoacusia sensorioneural implicam um grupo crescente de situaes, em que a leso se situa ao nvel da microvascularizao coclear, da que o conhecimento exacto da angiomorfologia normal se torne essencial na fase actual do conhecimento. A autora tem vindo a estudar, desde 1986, a angiomorfologia do ouvido Interno no modelo experimental, o Cobaio, utilizando vrias tcnicas microvasculares. sendo dado enfse particular neste estudo tcnica de microscopia electrnica de varrimento em moldes vasculares. Os animais usados no presente estudo pertencem espcie cavia porcellus, cobaio, por serem considerados na comunidade cientifica internacional como o melhor modelo experimental para estudo do ouvido interno, pelo facto de a morfologia coclear ser muito semelhante do Homem e por isso ser um modelo fivel para cirurgia experimental e microdisseco. Este estudo foi realizado em 100 cobaios, cavia porcellus, de ambos os sexos com peso mdio de 450g. A vascularizao do ouvido interno, no cobaio como no homem, faz-se atravs dos ramos de diviso da artria auditiva interna ou labirntica. A artria labirntica origina-se como ramo colateral da artria cerebelosa ntero-inferior a qual tem origem na artria basilar ou na artria vertebral. Embora no homem a artria auditiva interna possa tambm destacar-se da artria basilar e at da artria vertebral, no cobaio em todos os casos estudados a sua origem verificou-se sempre na artria cerebelosa ntero-inferior. A artria labirntica, ao passar abaixo do meato auditivo interno, divide-se na artria vestibular anterior e na artria coclear comum.A artria vestibular anterior dirige-se para o nervo vestibular, emite vasa nervorum para este nervo e vasculariza o utrculo e os canais semicirculares. A artria coclear comum origina dois ramos principais, a artria vestbulococlear ou vestibular posterior no cobaio, a qual se destaca junto espira basal da cclea e a artria coclear, como ramo terminal, que passa a denominar-se de artria modiolar ou espiralada, aps entrar no modolo. A artria modiolar ascende no modolo promovendo atravs dos seus ramos colaterais e dos seus ramos terminais a microvascularizao coclear, numa vascularizao de rgo de tipo terminal. Ao longo do seu trajecto verificouse de modo constante uma reduo gradual de calibre em cada uma das espiras, por emisso de ramos colaterais, sendo que o calibre da artria na base da cclea apresenta um valor que diminui gradualmente at ao pice. A artria modiolar origina em todo o seu trajecto ramos colaterais, cujo nmero diminui em valor absoluto da base para o pice: Arterolas radirias internas, arterolas de trajecto flexuoso que caminham junto s estruturas sensorioneurais da parede interna da cclea, junto ao lbio timpnico da lmina espiral ssea e na parede do prprio modolo, que se relacionam intimamente com este. As arterolas radirias internas originamse no flanco da artria modiolar espiralada. Contamse dez a doze em cada espira, extraordinariamente flexuosas desde a sua origem. As arterolas radirias internas originam como ramos colaterais, vrios grupos de arterolas de menor calibre, que vascularizam distintas regies da parede interna da cclea, as arterolas do gnglio espiral, a rede espiral interna, as arterolas de origem dos glomrulos de Schwalbe e a arterola da lmina basilar. As arterolas radirias externas importantes ramos colaterais da artria modiolar espiralada promovem a vascularizao de importantes estruturas da parede externa. Ao atingir o limite externo do ligamento espiral, as arterolas radirias externas dividemse em vrios ramos arteriolares de menor calibre, ao longo da convexidade do limite externo do ligamento espiral, originando a rede capilar ps-estriada que ocupa a poro lateral do ligamento espiral e a rede capilar ad -estriada, na sua poro mais medial em ntima relao com a estria vascular. A espira basal da cclea apresenta grande riqueza de vascularizao, com caractersticas particulares apenas a esta espira, a qual metabolicamente a mais exigente. A arterola da janela da cclea aborda a janela da cclea pela sua convexidade e divide-se numa rica rede vascular da qual emergem arterolas pr-capilares que se ramificam em capilares, os quais se dirigem em profundidade penetrando a rampa timpnica da cclea ao nvel da espira basal. Importou neste estudo verificar quais as semelhanas em termos de calibre de estruturas anlogas, na parede interna e na parede externa da cclea, com particular incidncia na rede capilar. Do estudo estatstico realizado com testes paramtricos de Tamahane e no paramtricos de Mann-Whitney, verifica-se que comparando todas as estruturas consideradas estas tm calibres diferentes, com excepo dos capilares da estria vascular e do ligamento espiral, pertencentes parede externa da cclea que tm calibres iguais aos capilares da rede espiral interna e aos capilares da parede interna da cclea, dependentes das arterolas da rede espiral interna. As redes capilares dependentes das arterolas radirias internas que vascularizam as estruturas sensorioneurais junto parede interna do modiolo so em tudo semelhantes em termos de calibre s redes capilares da parede externa da cclea, incluindo os capilares da estria vascular. Esta particularidade traduz num rgo com vascularizao de tipo terminal,um mecanismo de controlo do fluxo sanguneo coclear to importante na parede interna como na parede externa da cclea. ------------ ABSTRACT:Current studies on sensorineural hearing loss, imply a growing group of situations in which the lesion is located at the level of the cochlear microvasculature, hence the exact knowledge of normal angiomorfology becomes essential in current state of knowledge. The author has been studying since 1986, the angiomorfology of inner on the experimental model, the guinea pig, using various microvascular techniques being given particular emphasis in this study to the results of the technique of scanning electron microscopy on corrosion casts. The animals used in this study belong to the species cavia porcellus, guinea pig, to be considered in the international scientific community as the best experimental model for the study of the inner ear, the cochlear morphology is very similar to human and therefore a reliable model for experimental surgery and microdissection. This study was performed in 100 guinea pigs of both sexes with average weight of 450g. There shall be a brief description of embryology, anatomy and cochlear physiology in the light of developmental biology, regarding also the spatial location of the cochlea and the determinism of morphogenetic fields in their development and function. The cochlear transduction mechanism converts the sound wave in stimuli sound and so afferent auditory nerve fibres and deafness are closely related to the cochlear microvasculature. Cochlear ischemia is accompanied by immediate hearing loss. The different type of cochlear injury that leads to sensorineural deafness is well studied in presbycusis where an objective link with the audiometric pattern as been established. The sensory type of deafness, is closely related to the degeneracy of the organ of Corti and damage to the outer hair cells at the basal turn of the cochlea. Keeping in mind cochlear tonotopy with location of high frequency sounds at the level of the base of the cochlea, it explains the audiometric pattern with loss in high frequencies. The neural type of deafness, is characterized by neuronal loss with loss of descendant important neuronal afferents, with audiometric translation on a gradually curve with important loss of auditory discrimination. The metabolic type of deafness results in atrophy of the vascular stria, with consequent change in the potential of the endolymph by decreasing the vascular stria cells and changes in K + recycling mechanism. There is also a change in the morphology of the spiral ligament and the audiometric patern as a flattened curve with loss at all frequencies. Bearing in mind cochlear tonotopy and being characterized all types of sensorineural deafness, we may inquire to what extent the cochlear microvasculature, considering not only the cochlea as a whole but different regions of the inner wall and the outer wall of the cochlea, contributes to deafness. We analysed the entire cochlear morphology on scanning electron microscopy with particular emphasis on bone and membranous cochlea. The inner wall of the cochlea and intramodiolar structures such as the spiral ganglion, the morphology of its cell bodies and their axons are analyzed. The morphology of Cortis organ is described in detail, with description and large detail of the inner and outer hair cells. Is then presented the study of the microvasculature itself. The spiral modiolar artery is observed with the diaphanization technique and the technique of scanning electron microscopy on corrosion vascular casts. After emergence of collateral branches of the greatest importance, the radiating internal and external arterioles, the modiolar artery gives rise to its terminal branches, the arterioles of the cochear apex. Arterial vasa vasorum and vasa nervorum are displayed with a great detail, which was not yet described in such detail in previous microvascular studies. The arterial radiating arterioles originate in the flank of the spiral modiolar artery in number of ten to twelve in each loop, and they vascularize through their branches the inner wall cochlear sensorineural structures located in the modiolus as the spiral ganglion and structures near the organ of Corti. Their caliber is above 20 m on the basal turn and in the second loop it decreases to values between 12 and 20 m, decreasing progressively to the apex of the cochlea.They arise near the modiolus or on their way in the spiral lamina forming vascular loops, and divide without presenting vascular constrictions in their divisions, originating new vascular loops of lower caliber. Internal ratiating arterioles originate as collateral branches several groups of smaller caliber arterioles, which vascularize distinct regions of the inner wall of the cochlea namely, the arterioles of the spiral ganglion, the internal spiral network, the arterioles of origin of the glomeruli of Schwalbe and the arterioles of the basilar membrane. The glomeruli of Schwalbe play an important functional role as relay-stations, in hemodynamic terms, to control the cochlear microvasculature. External radiating arterioles have their origin in the spiral modiolar artery, they are directed towards the outer wall of the cochlea and run through the roof of the scala vestibuli. Above the insertion of Reissners membrane on the external wall the external radiating arterioles originate the spiral ligament arterioles, which vascularize the spiral ligament, they divide into several arteriolar branches of smaller caliber, along the convexity of the outer edge of the spiral ligament. The connective tissue of the spiral ligament forms a mesh with supporting function of the highly specialized epithelium, where pericytes were identifiable. Next to its base there is the microvascular network of stria vascularis. The adstriated vascular network which is divided into a capillary network, the capillary network of stria vascularis. The stria vascularis, the only vascularized epithelium of the human body, plays an important role, forming an haemato-labyrintine barrier to assure labyrinthine endocochlear potential and transport of ions, essential for the mechanism of transduction of external hair cells. The cochlear basal turn has a special feature on its external wall, the region of the windows, the round windows giving access to scala tympani and the oval window thatleads into scala vestibuli, and so it is metabolic demanding. For their role in cochlear tonotopy the sensorineural structures and those of the external wall of the cochlea, are particularly vulnerable to hypoxia. Although the complementarity of all the techniques was important for three- -dimensional reconstruction of the microvasculature of the cochlea, the scanning electron microscopy technique, especially when we used the system Semafore was fundamental to perform precise morphometric mesures regarding all vascular structures.Regarding the capillaries of the inner and outer wall of the cochlea networks this technique allowed their characterization in morphometric terms. To conclude the capillaries of the inner wall and of the external wall of the cochlea have similar size. So although located at different cochlear regions, with a different functional role, in cochlear physiology these networks consist of capillaries of similar caliber. It seems to translate a cochlear blood flow control mechanism that is so important in the inner wall as in and the external wall of the cochlea to provide for in inner ear homeosthasia.
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Directed Research Internship
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A Work Project, presented as part of the requirements for the Award of a Masters Double Degree in Finance from Maastricht University and NOVA School of Business and Economics
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This work project intends to evaluate the effectiveness of the Portuguese Governments strategy to promote the orderly deleveraging of the corporate sector in the context of the current economic crisis. The recommendations of the Troika and the commitments assumed under the Memorandum of Understanding signed by the Government in 2011 required the creation of formal processes to avoid disorderly deleveraging. Conclusions and recommendations were drawn based on past experiences of large-scale corporate restructuring strategies in other countries and on the analysis of financial and statistical data on companies applying for Programa Especial de Revitalizao.
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This paper aims to provide strategies for the organic supermarket chain Alnatura to shape the demand and its market share of the organic food & beverage (F&B) market in Germany within the next five years. Through the historic evolution and the current market assessment of Germany, compared to a benchmark country (US), as well as prospective trends in Germany, reasons and opportunities for market growth are evaluated. In addition, an industry attractiveness, competitor and company analysis is executed. Based on those findings and a conducted survey, suggestions to adjust Alnaturas current business strategies are deduced and finally examined on its risk and feasibility.
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The objective of this dissertation was to explore the German mens grooming market and to discuss the usage and purchase behavior of young male adults. After a brief market analysis, this dissertation evaluates the results of qualitative and quantitative research. The conducted research explored the consumers reasoning for and attitude towards personal grooming, and their attitude towards product attributes and the aging process. The dissertation concludes that men attach high value to personal grooming but only to the extent that their personal need is satisfied. As the male involvement in MG is highly dependent on each consumers individual needs, the market requires a careful segmentation.
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The quasi two-dimensional electron gas (q2DEG) hosted in the interface of an epitaxially grown lanthanum aluminate (LaAlO3) thin film with a TiO2-termi-nated strontium titanate (SrTiO3) substrate (001) has been massively studied in the last few years. The confinement of mobile electrons to within a few nanome-ters from the interface, superconductive behavior at low temperatures and elec-tron mobility exceeding 1000 cm2/(V.s) make this system an interesting candi-date to explore the physics of spin injection and transport. However, due to the critical thickness for conduction of 4 unit cells (uc) of LaAlO3, a high tunneling resistance hampers electrical access to the q2DEG, preventing proper injection of spin polarized current. Recently, our group found that depositing a thin overlayer of Co on LaAlO3 reduces the critical thickness, enabling conduction with only 1 uc of LaAlO3. Two scenarios arise to explain this phenomenon: a pinning of the Fermi level in the metal, inducing charge transfer in the SrTiO3; the creation of oxygen vacancies at the interface between LaAlO3 and the metal, leading to an n-type doping of the SrTiO3. In this dissertation, we will report on magnetotransport of metal/LaAlO3/SrTiO3 (metal: Ti, Ta, Co, Py, Au, Pt, Pd) heterostructures with 2 uc of LaAlO3 studied at low temperatures (2 K) and high magnetic fields (9 T). We have analyzed the transport properties of the gas, namely, the carrier concen-tration, mobility and magnetotransport regime and we will discuss the results in the light of the two scenarios mentioned above.
