The main objective of this thesis is to investigate the transient response and steady-state performance of a counter-cross flow liquid-to-air membrane energy exchanger (LAMEE). The LAMEE is constructed from several semi-permeable membranes which separate the air and liquid streams. In addition to heat transfer, moisture transfer occurs between the air and liquid streams since the membranes are permeable to water vapor. The LAMEE performance is assessed experimentally and the results are used to verify a numerical model. The verified numerical model is also used to extrapolate the transient and steady-state performance parameters to other test conditions. The transient response of the LAMEE is important since there are times when the LAMEE operates under transient conditions due to daily start-up or changing operating conditions such as flow rates, temperatures or humidities. The transient response of the LAMEE is investigated experimentally and numerically. The number of heat transfer units (NTU), and the ratio of solution and air heat capacity rates (Cr*) are two important parameters that affect the LAMEE performance. The results show that the transient sensible, latent and total effectivenesses increases with time after a step change in the conditions of the inlet liquid desiccant. The experimental and numerical transient effectiveness values and trends are compared for different NTU and Cr* values under summer and winter test conditions and the results show satisfactory agreement. In addition to the transient effectiveness, the time constant of the LAMEE is assessed as an important transient parameter. The time constant represents the time it takes for the LAMEE to reach 63.2% of the steady-state conditions after a step change in inlet conditions. The transient response of the outdoor air temperature and humidity ratio are normalized and used to determine the sensible and latent time constants. It is found that time constant depends on NTU, Cr* and thermal mass capacity of the LAMEE. The experimental and numerical results show that time constant increases as Cr* decreases or NTU increases. Furthermore, the verified numerical model is used to study the effect of outdoor air conditions on the LAMEE time constant. The numerical results reveal that the latent time constant is influenced by outdoor air conditions and the time constant decreases as H* increases, but the sensible time constant is almost constant for various outdoor air conditions. However, the outdoor air conditions affect the transient response of the LAMEE considerably since the total transient response of the LAMEE is closer to the latent transient response for the conditions studied. The steady-state performance of the LAMEE is studied for different NTU and Cr* values under summer test conditions. The experimental data are compared to numerical and analytical results and acceptable agreement is achieved. It is found that the steady-state effectiveness of the LAMEE increases with NTU and Cr*. The maximum total effectiveness reaches 88% for NTU=10 and Cr*=6.3. The verified numerical model is also used to investigate the effect of outdoor air conditions on the steady-state sensible and latent effectiveness of the LAMEE. The sensible effectiveness is significantly influenced by outdoor air conditions variation while the latent effectiveness is only slightly influenced by these variations. The sensible effectiveness decreases as the operating condition factor (H*) increases, but the latent effectiveness increases with H*.

Diabetic cystopathy is a chronic and common complication of diabetes with a classical triad of symptoms; decreased bladder sensation, increased bladder capacity and impaired detrusor muscle contractility (Hunter and Moore, 2003). In animal models of diabetes such as streptozotocin-induced diabetes in the rat, abnormalities of bladder function have been reported (Longhurst and Belis, 1986). The prototypic TRPV channel, TRPV1, is activated by capsaicin, which has been shown to cause contraction of the rat bladder (Saitoh et al., 2007), and this is reduced in STZ-diabetic rat bladder (Pinna et al., 1994). Therefore we hypothesize that TRPV1 function will be reduced in the diabetic bladder. The aim of this study are the following: Firstly, to investigate the effect of the streptozotocin (STZ) model of diabetes on a range of TRP channel functions in the urinary bladder smooth muscle preparation using TRP channel agonists and antagonists and to study the neurotransmitters involved in the contractile or relaxant responses. Some studies were also performed on colon tissues. Secondly, to explore the involvement of cholesterol modudation in TRP channel signalling. Thirdly, to study the change in TRP channel response with time following the treatment with streptozotocin. The results showed that the contractile responses to the TRPV1 agonist capsaicin, TRPV4 agonist 4-α-PDD, and TRPA1 agonist allyl isothiocyanate were significantly reduced in diabetic bladder. The selective TRPV1 antagonist, SB-366791, inhibited the contractile responses to capsaicin confirming the involvement of TRPV1 channels. The effect of diabetes is unlikely to be at the level of contractile machinery since the contractile responses to muscarinic receptor agonist carbachol were not significantly reduced in diabetic tissues. It is reported for the first time that the combination of neurokinin 1 and 2 antagonists GR-205171 and SB-207164 inhibited the contractile responses to capsaicin suggesting that a neurokinin may be the neurotransmitter involved in the capsaicin responses. In addition, the reduction of the responses to capsaicin in STZ-induced diabetic tissues occurred not only in urinary bladder but also in colon. Cholesterol-PEG significantly lowered the maximal contractile responses to capsaicin of rat bladder strips. Methyl-β-cyclodextrin, α-cyclodextrin and β-cyclodextrin at the same concentrations enhanced the contractile responses to capsaicin in the control and diabetic rat bladder strips. These effects of cyclodextrin are specific to capsaicin activated contractions and not seen with TRPA1 activation, suggesting that the effects are not mediated downstream of channel activation. Since α-cyclodextrin does not sequester cholesterol, the enhanced responses to cyclodextrins may not be due to the cholesterol modulations. Instead, theses novel findings may possibly occur by changing the local membrane lipid environment of the TRPV1 channel. As early as 36 hours after induction of diabetes by STZ, the contractile responses to capsaicin were significantly reduced in comparison to those of the controls and this reduction persisted until the eight weeks time point. In contrast, responses to the TRPA1 agonist allyl isothiocyanate were not affected at early time points but were reduced one week after STZ treatment. This detailed time course analysis suggests that there are novel mechanisms of modulation of the TRPV1 channels in this STZ model. In conclusion, in the rat urinary bladder or colon preparations, diabetes mellitus using STZ animal model caused 1) the impairment of a number of TRP channel subfamily functions, TRPV1, TRPV4 and TRPA1 but not TRPM8. The combination of NK1 and NK2 antagonists significantly inhibited the responses to capsaicin. This may suggest the involvement of neurokinin in postsynaptic transmission in rat bladder following the activation of TRPV1 channel, 2) the impairment caused by STZ-induced diabetes occurred very early (within 36 hours after diabetes induction) in TRPV1 channel but not TRPA1 channel. There are specific early effects of STZ treatment on TRPV1 channel function at a time when other afferent nerve terminal channels (TRPA1) are functioning normally, suggesting that early onset of dysfunction in TRPV1 signalling may not merely be the consequence of nerve damage, 3) the mechanism of this impairment may not be the effect of neuropathy on neurotransmitter release or nerve damage. Improving the responsiveness of nerves of bladder in diabetic patients might be of therapeutic benefit. The present studies suggest that it is possible to enhance function using indirect modulators such as bradykinin which potentiated the TRPV1 channel function in diabetic rat bladders.

Braking is mainly controlled by the engine. Friction between a pair of pads and a rotating disc converts the kinetic energy of the vehicle into heat. High temperatures can be reached in the system which can be detrimental for both, components and passenger safety. Numerical techniques help simulate load cases and compute the temperatures field in brake disc and brake pads. The present work implements a Finite Element (FE) toolbox in Matlab/Simulink able to simulate different braking manoeuvres used for brake dimensioning mainly in the early phase of car development process. The brake pad/disc geometry is considered as an axisymmetric body assuming negligible temperature gradient along the circumference of the disc. Calibration using three control factors namely: heat coefficient during braking , acceleration  and emissivity  for the implemented thermal model is performed using experimental investigation at Volvo Car Corporation (VCC) for three specific severe load cases. The thermal model is extended to measure brake fluid temperatures to ensure no vaporisation occurs. Simulation results of the brake disc and brake pad show good correlation with the experimental tests. A sensitivity analysis with the control factors showed convective coefficient during acceleration  the most sensitive, with temperature change of around 16%.

We employ an extreme ultraviolet (XUV) pulse to impulsively excite dipole polarization in atoms or molecules, which corresponds to coherently prepared superposition of excited states. A delayed near infrared (NIR) pulse then perturbs the fast evolving polarization, and the resultant absorbance change is monitored in dilute helium, dense helium, and sulfur hexafluoride (SF6) molecules. We observe and quantify the time-dependence of various transient phenomena in helium atoms, including laser-induced phase (LIP), time-varying (AC) Stark shift, quantum path interference, and laser-induced continuum structure. In the case of dense helium targets, we discuss nonlinear macroscopic propagation effects pertaining to LIP and resonant pulse propagation, which account for the appearance of new spectral features in transient lineshapes. We then use tunable NIR photons to demonstrate the wavelength dependence of the transient laser induced effects. In the case of molecular polarization experiment in SF6, we show suppression of XUV photoabsorption corresponding to inter-valence transitions in the presence of a strong NIR field. In each case, the temporal evolution of transient absorption spectra allows us to observe and understand the transient laser induced modifications of the electronic structure of atoms and molecules.

L'ébullition est présente dans la vie de tous les jours et elle a été par conséquent le sujet de beaucoup d'études, mais pour la plupart en régimes stationnaires. Néanmoins, l'intérêt de connaître les caractéristiques de l'ébullition transitoire est aussi important notamment pour la prévention des accidents nucléaires majeurs. C'est justement dans l'optique de mieux comprendre les phénomènes d'ébullition qui se produisent lors d'un RIA (Accident d'Insertion de Réactivité) que cette thèse a été financée par l'IRSN. Le RIA est un accident qui peut résulter d'une défaillance du mécanisme de la grappe contrôlant la réaction nucléaire. La réaction s'emballe pendant quelques dizaines de millisecondes (pulse de puissance) provoquant une augmentation rapide de la température du crayon de combustible et donc l'évaporation du liquide qui l'entoure. Des tests ont été faits par le passé soit sur des crayons de combustibles, soit sur des tubes chauffés ayant les mêmes dimensions qu'un crayon, afin d'améliorer la connaissance de ce phénomène. Par contre, les mesures étaient entachées d'incertitudes importantes, dues à des techniques de mesure non appropriées à des phénomènes si rapides. L'objectif de ce travail a été de concevoir et mettre en place une expérience capable de simuler un RIA à petite échelle, pour mieux comprendre les caractéristiques de l'ébullition lorsque la paroi monte en température très rapidement. De plus, ce dispositif expérimental devait être apte à étudier des montées en température moins violentes pour améliorer la connaissance de l'ébullition transitoire en général. Cette expérience a été conçue à l'Institut de Mécanique des Fluides de Toulouse. Elle est constituée d'une feuille métallique d'acier de 50µm d'épaisseur, formée en demi cylindre (8mm de diamètre et 200mm de longueur) et chauffée par effet Joule. Elle est entourée par du fluide réfrigérant HFE7000, qui permet de travailler en similitude par rapport au cas réel en eau. Le fluide est confiné par un deuxième demi cylindre en verre, ayant 34mm de diamètre. Les expériences peuvent être en vase ou avec écoulement, écoulement qui a été caractérisé par des mesures PIV. Plusieurs débits peuvent donc être employés et le sous-refroidissement du liquide est aussi ajustable. L'emploi d'une alimentation pilotable et très flexible permet d'obtenir des chauffages du métal jusqu'à 2500K/s, mais aussi des montées en température plus faibles, pour tracer des courbes d'ébullition stationnaires ou faiblement transitoires. La température de la paroi est mesurée grâce à une caméra infrarouge, couplée à des visualisations rapides et à des mesures de pression et température dans le liquide. / Boiling phenomena can be found in the everyday life, thus a lot of studies are devoted to them, especially in steady state conditions. Transient boiling is less known but still interesting as it is involved in the nuclear safety prevention. In this context, the present work was supported by the French Institute of Nuclear Safety (IRSN). In fact, the IRSN wanted to clarify what happens during a Reactivity-initiated Accident (RIA). This accident occurs when the bars that control the nuclear reactions break down and a high power peak is passed from the nuclear fuel bar to the surrounding fluid. The temperature of the nuclear fuel bar wall increases and the fluid vaporises instantaneously. Previous studies on a fuel bar or on a metal tube heated by Joule effect were done in the past in order to understand the rapid boiling phenomena during a RIA. However, the measurements were not really accurate because the measurement techniques were not able to follow rapid phenomena. The main goal of this work was to create an experimental facility able to simulate the RIA boiling conditions but at small scale in order to better understand the boiling characteristics when the heated-wall temperature increases rapidly. Moreover, the experimental set-up was meant to be able to produce less-rapid transients as well, in order to give information on transient boiling in general. The facility was built at the Fluid-Mechanics Institute of Toulouse. The core consists of a metal half-cylinder heated by Joule effect, placed in a half-annulus section. The inner half cylinder is made of a 50 microns thick stainless steel foil. Its diameter is 8mm, and its length 200mm. The outer part is a 34mm internal diameter glass half cylinder. The semi-annular section is filled with a coolant, named HFE7000. The configuration allows to work in similarity conditions. The heated part can be place inside a loop in order to study the flow effect. The fluid temperature influence is taken into account as well. A flexible power supply that can generate a free-shape signal, allows to get to a wall-temperature increase rate up to 2500 K/s but also to obtain lower rates, which permits to study weaker transients and steady state conditions. The thermal measurements are realised by means of an infra-red camera and a high-speed camera is employed in order to see the boiling phenomena at the same time. From the voltage and current measurements the heat flux that is passed to the fluid is known.

Quantum mechanical motion of electrons in atoms and molecules is at the heart of many photophysical and photochemical processes. As the natural timescale of electron dynamics is in the range of femtoseconds or shorter, ultrashort pulses are required to study such phenomena. The ultrashort pulse light-matter interaction at high intensity regime can however dramatically alter the atomic and molecular structures. Our current understanding of such transient electronic modification is far from complete, especially when complicated light-induced couplings are involved. In this dissertation, we investigated how a femtosecond strong-field pulse can control or modify the evolution of atomic or molecular polarization, representing electric dipole excitation in various systems. Extreme ultraviolet (XUV) attosecond pulse trains are used to coherently prepare superposition of excited states in various atomic and molecular systems. A subsequent phase-locked infrared (IR) femtosecond pulse is applied to perturb the dipoles, and transient changes in the transmitted XUV spectra are measured. This scheme is termed as XUV attosecond transient absorption spectroscopy. In the first study, we applied this technique to study the modification of Rydberg states in dilute helium gas. We observed several transient changes to the atomic structure, including the ac Stark shift, laser-induced quantum phase, laser-induced continuum structure, and quantum path interference. When the experiments were extended to the study of a dense helium gas sample, new spectral features in the absorption spectra emerged which cannot be explained by linear optical response models. We found that these absorption features arise from the interplay between the XUV resonant pulse propagation and the IR-imposed phase shift. A unified physical model was also developed to account for various scenarios. Extending our work to argon atoms, we studied how an external infrared field can be used to impulsively control different photo-excitation pathways and the transient absorption lineshape of an otherwise isolated autoionizing state. It is found that by controlling the field polarization of the IR pulse, we can modify the transient absorption line shape from Fano-like to Lorentzian-like profiles. Unlike atoms, in our study of autoionizing states of the oxygen molecule, we observed both positive and negative optical density changes for states with different electronic symmetries. The predictions of two distinct and simplified dipole perturbation models were compared against both the experimental results and a full theoretical calculation in order to understand the origin of the sign of absorption change. We relate this symmetry-dependent sign change to the Fano parameters of static photoabsorption. The same approach was applied to study molecular nitrogen, in which we observed the decay dynamics of IR perturbed doubly-excited Rydberg states with many vibrational progressions. In addition, we also conducted experiments to investigate Rydberg state dynamics of other molecular systems such as carbon dioxide. In summary, we experimentally explored the ephemeral light-induced phenomena associated with excited states of atoms and molecules. These studies provide real-time information on ultrafast electronic processes and provide strategies for direct time-domain control of the light-matter interaction.

Por muitos anos, a ciência tratou todas as redes como se seus relacionamentos fossem estabelecidos de forma randômica, ou seja, a maioria dos nós teriam aproximadamente o mesmo número de relacionamentos. Porém, o mapeamento de uma variedade de sistemas revelou que a maioria dos nós tinha poucos relacionamentos, enquanto alguns nós têm uma grande quantidade de conexões. Processos microscópicos dinâmicos e estatísticos são duas facetas de sistemas complexos, que estão intimamente ligadas, e a compreensão da sua interdependência é importante tanto para a previsão quanto planejamento estratégico. Os exemplos mais proeminentes incluem o ruído do tráfego em redes de comunicação, sinais ruidosos em sistemas desordenados e auto-organizados, e as séries temporais das flutuações dos preços nos mercados financeiros. Neste trabalho foram analisadas não apenas características globais do tráfego de pacotes em redes complexas, como a presença ou não de congestionamento na rede como um todo, mas também as características locais (isto é, de roteadores específicos) do tráfego no ponto de transição entre a fase livre e a fase de congestionamento. Os resultados mostram, entre outros, que a transição de um estado livre de congestionamento para o estado congestionado de um nó ocorre quando o coeficiente de detrended fluctuation analysis da série temporal do número de pacotes na fila de espera do nó é próximo do valor crítico de 1. / For many years the science networks all treated as if their relationships were set at random, that is, most of us have approximately the same number of relationships. However, the mapping in a variety of systems revealed that most of us had a few relationships, while some of us have a lot of connections. Dynamic and statistical microscopic processes are two facets of complex systems, which are closely linked, and understanding of their interdependence is important both for predicting as strategic planning. Prominent examples include traffic noise in communication networks, noisy signals in disordered systems and self-organized, and the time series of price fluctuations in financial markets. This work analyzed not only the overall characteristics of package traffic in complex networks and the presence or absence of congestion on the network as a whole, but also the local characteristics (ie, specific routers) of the traffic at the point of transition from the free phase, and congested phase. The results show, among others, that the transition from free to congested traffic in a node happens when the detrended fluctuation analysis coefficient of the time series of the number of waiting packets is close to the critical value of 1.

Thesis advisor: Philip G. Altbach / This is a phenomenological study of ten graduate international students at Chardin University (pseudonym). Through 30 in-depth interviews, multiple social contacts, and group and member checking sessions, stories emerged that highlight the social experiences of these graduate international students through their transient lives. Theoretical frameworks used to interpret the findings were transnationalism, adult transitional theory, and the graduate socialization model. This study provides a forum for participants to narrate their stories instead of being invisible and silent as they pass through our institutional corridors. What emerged from these narratives is that graduate international students cannot be grouped as one monolithic entity because they all lead variant and divergent lives. This research enumerates the intricacies, shades, and textures of their lives as they persist, succeed, and develop identities. In the past, graduate international students' social experiences have been portrayed in an oversimplified fashion, when in fact such students lead extremely complex lives as they negotiate a world that comprises both home and host country. Strongly lacking in the realm of social experiences have been meaningful relationships with American peers (looking beyond superficial ones), the university, and the local community. Operating within transnational social fields, regular prolonged conversations with family and friends from home tend to prevent participants from seeking out new connections in the United States. Most participants find comfort within their own ethnic enclaves, leading to cross-cultural isolation, which is still prevalent after decades of research conducted on this population. This study challenges universities to forge new pathways to engage with this vital and vibrant student body in meaningful, innovative, and creative ways. It is the responsibility of institutions of higher learning to understand the intricacies of their lives, as well as differences in religion, language, and socialization patterns. Universities need to find new ways to stay relevant in the lives of graduate international students during their tenure in the United States. / Thesis (PhD) — Boston College, 2010. / Submitted to: Boston College. Lynch School of Education. / Discipline: Educational Leadership and Higher Education.

Estudos recentes em materiais unidimensionais indicaram a necessidade de alterações na equação da dinâmica de captura de portadores por armadilhas. As experiências de Haarer e Möhwald em fenantreno PMDA mostraram que o tempo de captura das armadilhas decai linearmente com o campo elétrico, a partir de um campo crítico. Neste caso podemos admitir a substituição da fórmula clássica do tempo de captura pela razão entre a distância entre as armadilhas e a velocidade do portador sob ação do campo elétrico. A velocidade do portador devido ao campo é dada pelo produto da mobiliade do portador pelo campo elétrico. Assim, a equação de balanço de cargas nas armadilhas fica alterada pelo aparecimento explícito do campo elétrico, ocasionando mudanças no próprio processo de transporte. Neste trabalho, tentou-se encontrar o comportamento de materiais unidimensionais, na região de campo de ocorrência deste fenômeno e em suas proximidades, estudando-se a característica voltagem-corrente, bem como alguns processos transientes de tratamento analítico ameno. / Recent studies in one-dimensional systems show that the trapping equations must be changed. Haarer and Möhwald experiments on Phenanthrene PMDA showed that the trapping time decays linearly with the electric field, from a critical field on. Therefore we can assume that one should substitute the classical formula of the trapping time by the ratio between the intertrap distance and the drift velocity. The drift velocity is given by the product of the carrier mobility by the field. Thus the equation of carrier trapping becomes modified by the explicit dependence on the field that leads to changes in the transport itself. In this work we tried to find the response of a material in which such behavior is observed, by studying the current voltage characteristic, and also some transient processes amenable to analytical treatment.

No presente trabalho são apresentados resultados de simulação numérica transiente de um sistema de refrigeração doméstico de compressão a vapor considerando o procedimento descrito por JAKOBSEN (1995). O modelo matemático empregado se baseia num sistema de equações algébrico-diferenciais (EAD) de primeira ordem, obtido a partir do balanço de energia nos diferentes componentes do sistema de refrigeração, e de algumas outras relações necessárias para simular o comportamento global do sistema de refrigeração. O sistema de equações resultante é resolvido numericamente no software livre WinDali, da Universidade Técnica de Dinamarca. Dito software permite resolver sistemas de EADs que apresentam descontinuidades matemáticas usando o método de Runge- Kutta de quarta ordem. O modelo matemático empregado permite calcular a eficiência do sistema de refrigeração, predizer o consumo de energia, caracterizar termodinamicamente o sistema de refrigeração e suas interações, e descrever quantitativamente as perdas termodinâmicas (geração de entropia) do sistema funcionando em regime de operação. Esses resultados são obtidos em função da estratégia de controle do compressor, eficiência do compressor e do dimensionamento dos diferentes componentes do sistema de refrigeração. Os resultados comprovam que o modelo matemático e o programa computacional empregados permitem descrever corretamente o comportamento de um sistema de refrigeração doméstico, resultando numa ferramenta muito útil para otimização de refrigeradores domésticos. / In the present work are presented transient numerical simulation results of a vapor compression domestic refrigeration system considering the procedure described by JAKOBSEN (1995). The employed mathematical model is based on first order differential-algebraic equation (DAE) systems, obtained from energy balance in the different components of the refrigeration system, and from others relations that are necessary to simulate the global behavior of a refrigeration system. The resulting equation system is solved numerically in the free software WinDali developed at Technical University of Denmark. This software allows solving DAE systems that present mathematical discontinuities, using the Runge-Kutta method of fourth order. The employed mathematical model allows calculating the refrigeration system efficiency, predict the energy consumption, thermodynamically characterize the refrigeration system and its interactions and quantitatively describe the thermodynamic losses (entropy generation) of the system running in the operation regime. These results are obtained as a function of the compressor control strategy, compressor efficiency, and sizing of different components of the refrigeration system. The results confirm that the mathematical model and the computational program allow describing correctly the behavior of a domestic refrigeration system, resulting in a very useful tool for optimization of domestic refrigerators.