No description available.

No description available.

Caveolae are 50-60 nm flask-shaped invaginations of the plasma membrane that protect the plasma membrane from damage under stretch forces. They are highly abundant in cells that experience high levels of stress forces such as adipocytes, endothelial cells and muscle cells. Caveolae are generated by the oligomerisation and association of caveolin and cavin proteins, which form the caveolar coat complex at the caveolar bulb and are progressively well characterised. However, less is known about the proteins that localise to the caveolar neck. Using the CRIPSR/Cas9 system to generate gene knock-in and knockout cell lines, the role of EHD proteins at caveolae was investigated. It was found that, in addition to EHD2 being at the neck, both EHD1 and EHD4 were also present. The recruitment of other EHD proteins was markedly increased in the absence of EHD2. This functional redundancy was confirmed by the generation of EHD1, 2 and 4 triple knockout cell lines, which displayed two striking sets of phenotypes. Firstly, the characteristic higher-order clusters of caveolae are lost in the absence of EHD proteins. And secondly, caveolae are destabilised and the plasma membrane is more likely to rupture when the EHD1,2,4 knockout cells are subjected to cycles of stretch forces. The data identify the first molecular components that cluster caveolae into a membrane ultrastructure that potentially extends stretch buffering capacity. A second series of experiments tested different ideas about the function of caveolae in adipocytes. The insulin receptor and CD36 were found to at most partially colocalise with caveolae, and the role of caveolae in regulating signalling processes remains unclear. In contrast, the plasma membrane of adipocytes without caveolae is clearly more prone to rupture, confirming a mechanoprotective function.

No description available.

Alternating current electrohydrodynamics (ac-EHD) has been reported as a promising technique for enhancing sensor performance by the intimate mixing of the analyte solution at the electrode surface. The lateral fluid motion created by the ac-EHD phenomenon can be tuned by changing the frequency, voltage, and electrode geometry. To date, various studies have been conducted on the use of 2D electrodes based ac- EHD devices for sensor applications. However, the use of 3D electrodes may provide better fluid mixing as compared to the 2D electrodes due to the high surface area of the electrodes. To test this hypothesis, 2D and 3D microelectrodes with different sizes were designed and fabricated for ac-EHD studies using standard lithography and etching processes. Previous methods to achieve 3D microstructures and common issues faced during fabrication are also discussed. The lateral fluid motion created by the 2D and 3D electrodes after the application of different voltages and frequencies was analyzed by tracking the motion of fluorescent beads present in the mixing fluid. Fluorescence microscopy technique was used to capture videos of the movement of fluorescent beads in the fluid. The videos were analyzed using ImageJ to calculate the speed of fluorescent beads in the case of 2D and 3D electrodes. Furthermore, a different pattern of the fluid motion was observed in the case of 3D electrodes, which highlights the complex fluid movement in the case of 3D electrodes as compared to the 2D electrodes.

"The importance of two-phase heat transfer for thermal management of aerospace avionic systems has become increasingly important as these systems have become miniaturized. Embedded active cooling systems are used to remove heat from processors and other electronic components and transferring this heat to radiators or other heat exchangers. As the characteristic dimension of flow channels for two-phase flow becomes comparable to bubble size, the mini-channels (< 3 mm) used to direct the cooling fluid can complicate nucleate boiling heat transfer. Bubbles can encounter other heated walls, rapidly expanding and greatly reducing heat transfer as well as causing pressure oscillations and flow instabilities. The use of eletrohydrodynamic (EHD) effects, through the introduction of non-uniform electric fields, can help mitigate this problem by altering the behavior of nucleating bubbles. A combined experimental and computational study was undertaken using HFE-7100, an engineered fluid used in heat transfer applications, to investigate the potential for enhancement of nucleate boiling using EHD effects induced by applying a non-uniform electric field. In the experimental study, a minichannel was constructed consisting of an upper and lower copper electrode and glass side walls to allow visualization. The channel height and width were 3mm and 4.76 mm respectively, representative of the minichannel regime. The upper electrode was grounded while the lower electrode was heated and biased to high voltage. Optical imaging combined with post-processing and statistical analysis was used to quantify the effect of EHD on the bubble behavior. Bubbles were found to form preferentially on nucleation sites resulting from imperfections in the heated copper surface over artificially created nucleation sites. When a high voltage is applied across the electrodes, the electric field enhancement along the rim of the nucleation site is believed to influence the force balance on the forming bubble and thereby influence the bubble departure size and frequency. EHD forces also act on the bubble surface as a result of the variation in permittivity between the liquid and vapor phases, altering its shape as has been previously reported in the literature. Test results are presented that demonstrate that the application of EHD increases the nucleation site density on the heated surface and increase the bubble departure frequency from individual sites. In addition, test results are presented to show that EHD forces alter the shape of bubbles during growth and the vertical position of the detached bubbles as they are carried along in the cross flow. To better understand the underlying phenomena affecting the bubble shape and departure frequency, a numerical simulation of the bubble growth and departure was performed using COMSOL multiphysics software customized to incorporate a user-defined body force based on the Maxwell Stress Tensor. Tracking of the bubble surface, including coalescence and breakup was incorporated using the phase field variable method in which the Navier-Stokes and heat transfer equations are solved for each phase of the fluid. Results from the simulations confirmed the sensitivity of the bubble elongation and neck formation to the nucleation site geometry, specifically the angle along the rim where field enhancement occurs. The enhanced constriction of the bubble neck resulted in early detachment of bubbles when compared to simulations in which EHD was not applied. This finding provides some insight into the higher bubble departure frequency and nucleation site density observed in the experiment. The results from the combined experimental and numerical study suggest that EHD enhancement may provide a mechanism for extending the use of nucleate heat transfer to minichannels, thereby enabling additional options for cooling in compact, embedded systems. "

Electrohydrodynamic (EHD) micropumps have been developed and used in many diverse applications such as in microscale liquid cooling and various microfluidic systems. The objective of this research is to investigate different methods of enhancing the performance of ion drag EHD micropumps. In particular, the effect of electrode surface topology, applied electric field and doping agent in the dielectric liquid were investigated. The effect of 3D sharp features on the electrodes on charge injection in HFE 7100 as dielectric fluid was studied under an applied DC electric field. Micro and nano-scale features with high aspect ratio were developed on smooth copper electrodes by chemical etching or through electrophoretic deposition of single walled carbon nanotube (SWCNT). The spacing between the electrodes was kept at 250 µm. A reduction factor of 5 was achieved for SWCNT electrodes compared to the smooth case for the onset of charge injection. This study was then extended to determine its effects on the performance of ion drag EHD micropumps with 100 pairs of interdigitated electrodes. The emitter electrodes (20 µm) were half the width of the collector electrodes (40 µm), with one pump having an inter-electrode spacing of 120 µm and the other with 40 µm. Each micropump had a width of 5 mm and a height of 100 µm. SWCNT was deposited on the emitter electrodes of the micropump to generate a maximum static pressure of 4.7 kPa at 900 V, which is a 5 fold increase compared to the pump with smooth electrodes. Flow rate at no back pressure condition was improved by a factor of 3. The effect of Ferrocene as a doping agent in the working fluid HFE 7100 was studied under DC voltages. A maximum static pressure of 6.7 kPa was achieved at 700 V with 0.2% weight based doping agent, 11 times higher than when there was no doping agent at the same applied voltage. When there was no back pressure the pump generated a maximum flow rate of 0.47 mL/min at 700 V with 0.05% doping agent which is 9 times greater than with no doping agent. The effect of pulsed voltage on the performance of ion drag EHD micropump has been studied to exploit the displacement current at the sudden change of applied voltage magnitude. A range of pulse repetition rate and duty cycle were found to significantly enhance the pump performance. Static pressure generation was up to 75% and 88% greater at an optimal pulse repetition rate and duty cycle, respectively, compared to the average of the two DC levels. The effect of external flow on the discharge characteristics of an injection micropump was studied with DC volts. Higher discharge current and lower threshold voltage for the onset of charge injection in case of co-flow compared to the static case was observed. There was an optimum flow rate to generate maximum current for both co and counter-flow cases. / Thesis / Doctor of Philosophy (PhD)

Les émissions de polluants dans l’atmosphère représentent l’un des objectifs majeurs à l'heure actuelle. Dans le domaine automobile, la réduction des émissions de CO2 repose en partie sur l’amélioration du rendement moteur. Pour ce faire, ces travaux de thèse sur la texturation de surface à micro et nano échelle proposent de diminuer les pertes par frottements dans les moteurs thermiques alternatifs à combustion interne. Le poste moteur retenu dans cette thèse est le segment/piston/chemise car près de 40 % des pertes par frottement y sont générées. On s’intéresse à la texturation par LASER femtoseconde de cavités sur la surface du segment coup de feu. Le comportement tribologique de surfaces texturées est étudié en régime ElastoHydroDynamique (EHD) et Limite. En régime EHD, la capacité de formation d’un film lubrifiant et le contrôle du frottement en surface texturée indique un comportement tribologique dépendant du couplage entre les paramètres expérimentaux - cinématique des surfaces, pression de contact, taux de rétention en huile et temps de résidence des textures dans le contact et les paramètres géométriques - diamètre, profondeur, densité de textures. En régime Limite, l’influence des textures sur le comportement tribologique a permis de confirmer l’hypothèse sur le rôle de piégeage des débris par les cavités et de mettre en évidence des configurations de réseaux réduisant le coefficient de frottement pour des profondeurs faibles. / Nowadays pollutant emissions in the atmosphere are at stake. In the field of automotive industry, the reduction of CO2 emissions lies mostly on improving engine efficiency. This study about textured surface on micro- and nano-scale aims to diminish the friction losses in internal combustion engine.The main element is the piston ring pack because of the creation of 40 percent in friction losses. This analysis consists in LASER texturing with cavities on the surface of the first piston ring. The tribological behavior of textured surfaces is lead in Boundary and ElastoHydroDynamic (EHD) regime. In EHD regime the impact on load capacity of lubricant and frictional behavior in textured surface show linking between experimental parameters as surfaces cinematic, contact pressure, retention volume of oil, the dwelling time of cavities and the geometrical parameters as diameter, cavity depth and cavity density. In Boundary lubrication, the effect of cavities on tribological behavior has led to confirm the hypothesis of trapped debris in the cavities and to make in evidence swallow network of cavities reducing friction coefficient.

This diploma thesis deals with the influence of the surface texturing of non-conformal surfaces at the friction coefficient. In the work were made adjustment of experimental apparatus for measuring friction in the contact between ball and flat disk. Friction coefficient was calculated by the size of the torque on the ball, which was measured by the torque sensor. For recording and processing signal from the sensor was designed software that makes it possible to measure the coefficient of friction for selected conditions (loading of contact, speed of rubbing surfaces and rolling-sliding conditions). Experiments were carried out with smooth and textured ball, glass, and steel disc at different speeds and rolling-sliding conditions. To determine the effect of the influence of the surface texturing at the friction coefficient the size of the coefficient of friction of smooth and textured ball was compared. It was found that the microtexture of the friction coefficient has little effect.

This diploma thesis deals with experimental study of the effect of surface grooves on distribution of lubricant film in elastohydrodynamic lubricated point contact. Lubricant film thickness was measured by ball-on-disc apparatus using an optical interferometry technique - thin film colorimetric interferometry. The effects of groove geometry, lubricant and operating conditions were studied in this diploma thesis. The effects of these variables are evaluated based on newly suggested parameter Rgi (groove influence ratio). Groove influence ratio is defined as an influenced film thickness influenced by groove divided by film thickness for smooth surfaces.