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Mazzawi N.,Technion - Israel Institute of Technology | Postema M.,University of Bergen | Postema M.,The Michelsen Center for Industrial Measurement Science and Technology | Kimmel E.,Technion - Israel Institute of Technology
Acta Physica Polonica A | Year: 2015

The bilayer sonophore model suggests that ultrasound induces a pulsating structure in the intra-membrane hydrophobic space between the two lipid monolayer leaflets of the cell membrane, assembled by dissolved gas of the surrounding area, which absorbs acoustic energy and transforms it by creating intra-cellular structural changes. This void has been referred to as a bilayer sonophore. The bilayer sonophore inflates and deflates periodically when exposed to ultrasound and may itself radiate acoustic pressure pulses in the surrounding medium in the same way a gas bubble does: once exposed to ultrasound the bilayer sonophore becomes a mechanical oscillator and a source of intracellular cavitation activity. In this paper, we describe observations of the clustering behaviour of living cells and several other particles in a standing sound field generated inside a ring transducer. Upon sonication, blood cells and monodisperse polystyrene particles were observed to have been trapped in the same locations, corresponding to nodes of the ultrasound field. Because polystyrene is hydrophobic, it behaves like a particle trapped inside a thin gas shell. In fact, the sonophore model treats biological cells in a similar way. Microbubbles that form the ultrasound contrast agent Quantison™ behave differently, however. These microbubbles accumulated in circles faster than blood cells and polystyrene particles. In addition, they form tightly packed clusters at the nodes, indicating very strong secondary Bjerknes forces. Cluster formation is not to be expected in cells with predicted sonophore sizes on the order of 10-100 nm.

Helseth L.E.,University of Bergen | Helseth L.E.,The Michelsen Center for Industrial Measurement Science and Technology
Journal of Colloid and Interface Science | Year: 2012

Complexes of dyes and polyelectrolytes have found widespread use in a variety of functional materials and interfaces. Here it is found that upon mixing the anionic dye pyranine and a cationic polyelectrolyte, poly(allylamine-hydrochloride), two different colloidal structures may form. Above a certain concentration of anionic dye, crosslinking of the polyelectrolyte is initiated, and the formation of sheet-like colloidal structures was observed. Addition of hydroxyl ions resulted in the formation of micron-sized spherical colloids. It was also found that the colloidal shape transition was accompanied by a significant red-shift in the fluorescence emission. Combining fluorescence measurements with studies of the particle size with time, it was found that red-shift was related to the crosslinking of the dye and the polyelectrolyte, and was not influenced significantly by the aggregation and particle growth. Further information about the colloidal behavior and stability was obtained by letting droplets dry and follow the kinetics of this process. It was found that the particles collapsed near the contact line and formed a ring deposit, in agreement with previous studies. However, unlike previous studies, the thickness of the ring deposit did not grow significantly with time, due to the peculiar process of formation found here. © 2012 Elsevier Inc.

Bruvik E.M.,University of Bergen | Hjertaker B.T.,University of Bergen | Hjertaker B.T.,The Michelsen Center for Industrial Measurement Science and Technology | Hallanger A.,Christian Michelsen Research
Flow Measurement and Instrumentation | Year: 2010

Gamma-ray tomography is a technique well suited to visualize gas void fraction distribution in two-phase flows. The liquid phase considered in this paper is a homogeneous mixture of oil and water. Gamma-ray tomography will be used to qualitatively visualize the distribution of gas in the flow, and also to provide more quantitative average void fraction measurements. The subject treatment is practical and experimental with a primary focus on multiphase sampling. Experimental results for total average void fraction are compared to the drift-flux model for two-phase flow by comparing measurements with the calculated slip. © 2009 Elsevier Ltd.

Maad R.,University of Bergen | Maad R.,The Michelsen Center for Industrial Measurement Science and Technology | Hjertaker B.T.,University of Bergen | Johansen G.A.,University of Bergen | Olsen T.,University of Bergen
Flow Measurement and Instrumentation | Year: 2010

A HSGT (High Speed Gamma-ray Tomograph) has been designed and built at the University of Bergen with the objective to monitor rapid changes in multiphase hydrocarbon flow regimes. In order to perform real-time image reconstruction with photon integration times as low as 10 ms, a novel DACS (Data Acquisition and Control System) has been developed. The DACS is based on FPGA (Field-Programmable Gate Array) programming of the CompactRIO module from National Instruments to minimize its data acquisition and control time. The CompactRIO module includes a reconfigurable FPGA, which provides hardware-level data acquisition and control determinism with a time resolution of 25 ns. The data acquisition and control time for the HSGT obtained with the novel DACS interface design is 0.18 ms, which corresponds to a data transmission bandwidth of 1.35 Mbytes/s given that the HSGT data frame consists of 85 channels each comprising a 24 bit resolution. The DACS also facilitates FPGA sensor data pre-processing, i.e. normalization, of the acquired tomograph data to speed up the image reconstruction. Dynamic characterization of the HSGT for rotational and translational movements is presented in this paper, which is based on calculation of the RMSE (Root Mean Square Error) of the acquired tomogram compared to that of the test phantom. The test phantom consists of two spherical holes with different radius in a polypropylene sample. The results of the dynamic characterization show that the HSGT can sustain imaging of a rotational object with angular velocities ~30 rad/s. For translational movement (free fall) the HSGT is able to detect internal cross-sectional structures with velocities up to ~4 m s-1. © 2010 Elsevier Ltd.

Saetre C.,University of Bergen | Saetre C.,The Michelsen Center for Industrial Measurement Science and Technology | Tjugum S.-A.,The Michelsen Center for Industrial Measurement Science and Technology | Anton Johansen G.,University of Bergen | Anton Johansen G.,The Michelsen Center for Industrial Measurement Science and Technology
Radiation Physics and Chemistry | Year: 2014

Measurement of multiphase pipe flow of gas, oil and water is not at all trivial and in spite of considerable achievements over the past two decades, important challenges remain. These are related to reducing measurement uncertainties arising from variations in the flow regime and the fluid properties, improving long term stability and developing new means for calibration, adjustment and verification of the multiphase flow meters. In this work the pipe flow is split into temporal segments using multiple gamma-ray measurements. One 241Am source with principal emission at 59.5keV was used because this relatively low energy enables efficient collimation and thereby shaping of the beams, as well as use of compact detectors. One detector is placed diametrically opposite the source whereas the second and eventually the third are positioned to the sides so that these beams are close to the pipe wall. The principle is then straight forward, that is to compare the measured intensities of these detectors, and through those identify the instantaneous cross sectional gas-liquid distribution, i.e. the instantaneous flow pattern. By counting the intensity in short time slots of <100ms, experiments verify that rapid variations exist. The water salinity is one of the fluid properties which challenge most multiphase flow meters because its variations affects component volume fraction calculations based on gamma-ray, electrical conductance and other measurements methods. At the University of Bergen a dual modality method has been developed using simultaneous measurements of transmitted and scattered gamma-rays from a 241Am source. This allows the gas volume fraction to be determined independent of changes in the water salinity, provided that the fluid is fairly homogeneously mixed. Tomographic flow segmentation allows selection of low gas fraction segments where the salinity, in combination with running averaging methods, can be calculated with higher accuracy. © 2013 Elsevier Ltd.

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