Hydrate film growth has been examined at the hydrocarbon/water interface for cyclopentane and methane hydrate. Video microscopy was used to measure hydrate film thickness, propagation rate across the hydrocarbon/water interface and gas consumption measurements characterized the hydrate formation mechanism. Cyclopentane and methane hydrate film formation were measured over the temperature range of 260–279K and pressure range of atmospheric to 8.3MPa. Hydrate formation was initiated by the propagation of a thin, porous film across the hydrocarbon/water interface. The propagation rate and thickening of the hydrate film was strongly dependent on the hydrate former solubility in the aqueous phase, in the absence and presence of hydrate. Cyclopentane hydrate film thickness began at ~12 μm and grew to a final thickness (15–40 μm) which increased with subcooling. Methane hydrate film thickness began at ~ 5 μm and grew to a final thickness (20–100 μm) which also increased with subcooling. The hydrate film grew into the water phase. Gas consumption measurements indicated that the aqueous phase supplied hydrate former during the initial hydrate growth, and the free gas supplied the hydrate former for film thickening and development. Hydrate film formation at the hydrocarbon/water interface was proposed to consist of three consecutive stages: propagation, development and bulk conversion.

This work deals with the problem of pipeline plugging by gas hydrates during oil production. Gas hydrates are crystals resulting from water and gas molecules association under high pressure and low temperature conditions. Such thermodynamical conditions are generally encountered during oil production and transport, particularly in deep offshore fields or in cold areas. Due to an agglomeration process which is still debated, hydrate occurrence can lead to plug formation. This study aims at improving the understanding in this mechanism process, in the case of water-in-oil emulsions. Therefore, ice or hydrate particle agglomeration is compared. Ice or trichlorofluoromethane (CCl3F) hydrate particles dispersed in xylene with asphaltenes as surfactant is chosen as a model system. As CCl3F hydrates are stable under atmospheric pressure, it allows us to apply different techniques without being limited by high pressure conditions. The Nuclear Magnetic Resonance (NMR) technique is used. The very different relaxation rate for solids or liquids is used to monitor in situ the ratio between solid and total hydrogen or fluorine as a function of time with controlled shearing conditions. Thus, a kinetic study is realized, that enabled to know the amount of ice formed. The apparent viscosity of the system, during crystallization and plugging, is also followed with rheometry in order to characterize agglomeration. This experimental approach allows us to highlight that physico-chemistry of interface water/oil has an important role in agglomeration. It enables us to discuss different mechanisms of agglomeration of ice and hydrate particles in a hydrocarbon phase.

The experimental formation of natural gas hydrate on pendant water droplet exposed to natural gas was conducted and visually observed under the pressures from 3.86MPa to 6.05MPa. The temperature was set at 274.75K and 273.35K. The diameter of the pendant water droplet was around 4mm. The nucleation and growth of hydrate film on the pendant water drop exhibited a generalized trend. The film initially generated at the boundary between the water drop and suspension tube, and afterwards grew laterally and longitudinally on the surface of the water drop. The phenomenon of the two layers of hydrate films growing on the pendant water drop distinguished from the experiments on the sessile water drop. The effect of the driving force that resulted from the overpressure from the three equilibrium pressure on the hydrate nucleation and growth was investigated. It was found that the elevation of the driving force reduced the nucleation time and shortened the process of the hydrate growth on the pendant water drop. The crystals on the hydrate shell became coarser with the increase of the driving force. The mechanism for the hydrate film formation and growth on static pedant water droplet included four stages, such as nucleation, generation of the hydrate film, growth of the hydrate film, and hydration below the hydrate shell.

No description available.

Crystallization is done in the sugar industry using natural circulation vacuum evaporative crystallizers known as vacuum pans. the fluid which is known as massecuite consists of a suspension of crystals in concentrated molasses. It is highly viscous and slightly non-Newtonian, and laminar conditions prevail in the apparatus. Research on forced convection boiling heat transfer, pressure drop and vapour holdup has been done mostly in turbulent flow under pressures higher than atmospheric, but no studies have been made when boiling viscous fluids under vacuum. This thesis describes a series of experiments which were undertaken with the following objectives: (a) to determine the influence of the pertinent variables on heat transfer, friction losses and vapour holdup while boiling under laminar conditions (b) to produce a method for the calculation of the evaporation and circulation rates in vacuum pans, as this would make possible the optimization of this type of equipment. The apparatus used consisted of a single tube steam heated forced circulation evaporator. The void fraction, pressure and centerline temperature were measured along the tube. The fluids used were syrup, molasses and massecuite covering a thousandfold change in viscosity. The tests were conducted under different conditions of vacuum and steam pressures with varying tube inlet velocities. The experimental results show that the boiling heat transfer coefficient can be correlated as a function of the two phase Reynolds number and dimensionless density ratio and that it is inversely proportional to the tube length to the power of one third. The pressure drop can be estimated using the equation of Oliver and Wright (1964) for bubbly flow. Equations are proposed for calculating the void fraction in the highly subcooled region and point of bubble departure. These equations form the basis of a computer program which by a stepwise and iterative method simulates the boiling process along the tube. Measurements taken on a natural circulation pan with tubes of different length show that this method predicts the effect of the tube length with reasonable accuracy. The limitations of this study are that the experiments were done with a single diameter tube so that the effect of diameter has not been established with certainty. Only sugar products were used in the experiments, and caution is necessary if this method is applied to other fluids. / Thesis (Ph.D.)-University of Natal, Durban, 1985.

The image analysis techniques presented in the présent thesis have been developed as part of a European projeet dedicated to the development of an automatic membrane protein crystallization pipeline. A large number of samples is simultaneously produced and assessed by transmission electron microscope (TEM) screening. Automating this fast step implicates an on-fine analysis of acquired images to assure the microscope control by selecting the regions to be observed at high magnification and identify the components for specimen characterization.The observation of the sample at medium magnification provides the information that is essential to characterize the success of the 2D crystallization. The resulting objects, and especially the artificial membranes, are identifiable at this scale. These latter present only a few characteristic signatures, appearing in an extremely noisy context with gray-level fluctuations. Moreover they are practically transparent to electrons yielding low contrast. This thesis presents an ensemble of image processing techniques to analyze medium magnification images (5-15 nm/pixel). The original contribution of this work lies in: i) a statistical evaluation of contours by measuring the correlation between gray-levels of neighbouring pixels to the contour and a gradient signal for over-segmentation reduction, ii) the recognition of foreground entities of the image and iii) an initial study for their classification. This chain has been already tested on-line on a prototype and is currently evaluated.

No description available.

Parasites of phylum Apicomplexa cause devastating diseases on a global scale. Toxoplasma gondii, the etiological agent of toxoplasmosis, and Plasmodium falciparum, the most virulent agent of human malaria, have the most substantial effects on human health and are the most widely studied. The success of these parasites is due in part to a sophisticated molecular arsenal that supports a variety of novel biological processes including a unique form of host cell invasion. Accessing the protective environment of the host cell is paramount to parasite survival and is mediated through an active invasion process: the parasite propels itself through a circumferential ring known as the moving junction (MJ) formed between its apical tip and the host cell membrane. The MJ ring is comprised of a parasite surface protein (AMA1) that engages a protein secreted by the parasite into the host cell and presented on the host cell surface (RON2). Thus, through an intriguing mechanism the parasite provides both receptor and ligand to enable host cell invasion. Prior to the studies described herein, the characterization of the AMA1-RON2 association was limited to low-resolution experiments that provided little insight into the functional and architectural details of this crucial binary complex. Towards elucidating the mechanism of AMA1-RON2 dependent invasion, I first structurally characterized T. gondii AMA1 bound to the corresponding binding region of RON2; analysis of the AMA1-RON2 interface along with biophysical data revealed an intimate association likely capable of withstanding the shearing forces generated as the parasite dives through the constricted MJ ring. To investigate the role of the AMA1-RON2 complex across genera, species and life-cycle stages, I next characterized the AMA1-RON2 complex from a distantly related genus within Apicomplexa (Plasmodium) and from a divergent pairing within T. gondii. By combining structural, biophysical and biological data, I was able to generate a detailed model describing the role of AMA1 and RON2 in MJ dependent invasion, which is currently supporting efforts to develop novel vaccines and cross-reactive small molecule therapeutics. / Graduate / 0487 / tonkin.ml@gmail.com

14th International Summer School on Crystal Growth ( 1–7 August 2010, Dalian (China))

Human Immunodeficiency Virus (HIV) has become a global pandemic with at least 25 million deaths and no cure. One of the most important targets to inhibit this virus is HIV-1 protease (PR), which is required to cleave the viral proteins needed for maturation of the virus after it invades and replicates in the host cell. There are nine protease inhibitors that are used in AIDS treatment. The virus loses susceptibility to these inhibitors by drug resistance due to mutations. The goal of the project is to examine the highly drug resistant HIV PR P51 in its complex with inhibitors. In this experiment we expressed and purified HIV PR P51 protein. We performed protein crystallization with inhibitors Tipranavir, Amprenavir, Darunavir, and Saquinavir to obtain the structure of the protease and the inhibitors in their complexes. Future analysis of the crystal structures will help with the development of successful therapeutic inhibitors.