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Jure Derganc - One of the best experts on this subject based on the ideXlab platform.
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controlled shaping of lipid vesicles in a microfluidic Diffusion Chamber
RSC Advances, 2017Co-Authors: Mojca Mally, Bojan Božic, Vrhovec S Hartman, U Klancnik, Sasa Svetina, Jure DergancAbstract:Synthetic lipid vesicles represent an important model system for studying membrane processes, which often depend on membrane shape, but controlled shaping of vesicles remains a challenging experimental task. Here, we present a novel method for shaping giant lipid vesicles by independently regulating osmotic conditions and the concentration of membrane-shaping molecules, which intercalate into the membrane and drive membrane bending. The method is based on the microfluidic Diffusion Chamber, where the solution around the vesicles can be repeatedly exchanged solely by Diffusion, without any hydrodynamic flow that could deform the membrane. By using lipopolysaccharide (LPS) as a vesicle shape-modifying molecule, we demonstrate controlled and reversible transformations across three shape classes, from invaginated to evaginated vesicles. We show that extensive shape transformations can lead to shapes that are assumed to comprise narrow membrane necks that hinder equilibration of the membrane and the vesicle interior. All the observed shapes are in good agreement with the predictions of the area-difference-elasticity model applied to the vesicles that were denser than their surrounding solution. Our results validate the microfluidic Diffusion Chamber as a universal framework for membrane shaping that could also pave the way towards controlled fabrication of synthetic membranes resembling cell-compartments with large surface-to-volume ratios.
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a microfluidic Diffusion Chamber for reversible environmental changes around flaccid lipid vesicles
Lab on a Chip, 2011Co-Authors: Sasa Vrhovec, Mojca Mally, Blaž Kavcic, Jure DergancAbstract:The reversible environmental changes around flaccid lipid vesicles represent a considerable experimental challenge, particularly because of remarkable softness of flaccid membranes, which can warp irreversibly under the slightest hydrodynamic flow. As a result, we have developed a microfluidic device for the controlled analysis of individual flaccid, giant lipid vesicles in a changing chemical environment. The setup combines the advantages of a flow-free microfluidic Diffusion Chamber and optical tweezers, which are used to load the sample vesicles into the Chamber. After a vesicle is loaded into the Diffusion Chamber, its chemical environment is controllably and reversibly changed solely by means of Diffusion. The Chamber is designed as a 250 micrometres-long and 100 micrometres-wide dead-end microchannel, which extends from a T-junction of the main microchannels. Measurements of the flow-velocity profile in the Chamber show that the flow rate decreases exponentially and scales linearly with the flow rate in the main channel. The characteristic length of the exponential decrease is 15 (1 ± 0.13) micrometres, meaning that a large part of the Diffusion Chamber is effectively flow-free. The Diffusion properties are assessed by monitoring the Diffusion of a dye into the Chamber. It was found that a simple 1D Diffusion model fits well to the experimental data. The time needed for the exchange of solutes in the Chamber is of the order of minutes, depending on the solute's molecular weight. Here, we demonstrate how the Diffusion Chamber can be used for reversible environmental changes around flaccid, giant lipid vesicles and membrane tethers (nanotubes).
Dragoslav Nikezic - One of the best experts on this subject based on the ideXlab platform.
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Rn progeny Diffusion, deposition and track distribution in Diffusion Chamber with permeable membrane
Radiation Measurements, 2019Co-Authors: V.m. Markovic, N Stevanovic, A.g. Markovic, Dragoslav NikezicAbstract:Abstract Objective of this work is to define method by which sensitivities of CR-39 and LR-115 in Diffusion Chamber could be determined. Method is based on initial physical processes that occurs in Diffusion Chamber: Diffusion, deposition and decay of radon (isotopes 222Rn and 220Rn) and their progeny. Cylindrical shape of Chamber was considered due to availability of experimental data for validation of presented method. The shape was not limitation factor and can be extended to any geometry. Diffusion equations for radon in two mediums (membrane and Chamber volume) and their progeny in volume were solved using Finite Difference Method – FEM, and solutions are their spatial distributions inside of Diffusion Chamber. Calculation of flux towards the Chamber walls determine distribution pattern and deposited progeny fractions. It has been shown that volume and deposited distributions are not uniform. Visible tracks on CR-39 for defined etching conditions are determined by considering range of alpha particles in air and empirical critical angle function θ C = θ C ( E ) . For LR-115 mean critical angle of 〈 θ c 〉 = 50 0 and energy window from E min = 1.7 MeV to E max = 4.2 MeV was adopted from literature to determine number of visible tracks. The track density distributions on detector are found to be non-uniform and radially dependent. Thickness of permeable membrane has important influence on presence of thoron and its progeny tracks on detector. Sensitivities of CR-39 and LR-115 in Diffusion Chamber were determined using method presented in this work and compared with other theoretical models and experiment with good agreement. This shown applicability of the presented method. One of important conclusion is that detector sensitivity, given as one simple number, is not the best parameter for calibration due to the existence of radial variation of track density. For cylindrical Chamber with 10 cm length and 4 cm radius, covered with membrane in form of one-layer filter paper 0.25 mm thickness, and for equal concentrations of 222Rn and 220Rn in front of the Chamber, contribution of 220Rn and its progeny to total track density is about 3%.
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Time dependence of 222Rn, 220Rn and their progenies’ distributions in a Diffusion Chamber
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2017Co-Authors: N Stevanovic, V.m. Markovic, Dragoslav NikezicAbstract:Abstract Diffusion Chamber with SSNTD (Solid State Nuclear Track Detector) placed inside is a passive detector for measuring the activity of 222 Rn and 220 Rn (radon and thoron) and their progenies. Calibration from detected alpha particle tracks to progeny activity is often acquired from theoretical models. One common assumption related to these models found in literature is that concentrations of 222 Rn and 220 Rn at the entrance of a Chamber are constant during the exposure. In this paper, concentrations of 222 Rn and 220 Rn at the entrance of the Chamber are taken to be variable with time, which is actually the case in reality. Therefore, spatial distributions of 222 Rn and 220 Rn and their progenies inside the Diffusion Chamber should be time dependent. Variation of 222 Rn and 220 Rn concentrations on the entrance of the Chamber was modeled on the basis of true measurements. Diffusion equations in cylindrical coordinates were solved using FDM (Finite Difference Method) to obtain spatial distributions as functions of time. It was shown that concentrations of 222 Rn, 220 Rn and their progenies were not homogeneously distributed in the Chamber. Due to variable 222 Rn and 220 Rn concentrations at the entrance of the Chamber, steady state (the case when concentration of 222 Rn, 220 Rn and their progenies inside the Chamber remains unchanged with time) could not be reached. Deposition of progenies on the Chamber walls was considered and it was shown that distributions of deposited progenies were not uniform over walls’ surface.
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Response of Diffusion Chamber with LR115 detector and electret to radon and progeny
Radiation Measurements, 2009Co-Authors: Dragoslav Nikezic, Dragana Krstic, Svetislav SavovićAbstract:Cylindrical Diffusion Chamber for radon measurement equipped with nuclear track detector (LR115) and electret, was considered in this work. Electrets were used to attract positively charged radon progeny created by radon decay inside a Chamber. Sensitivity of such setup has been determined for different distances between electret and LR115 detector. A possibility of progeny separation was observed, due to the existence of upper energy detection limit of LR115. Different geometries of detector and electret were tested in order to optimize this kind of device.
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Influence of an electret on the sensitivity of CR-39 nuclear track detector in Diffusion Chamber
Indian Journal of Physics, 2009Co-Authors: Dragoslav Nikezic, Dragana KrsticAbstract:Cylindrical Diffusion Chamber for radon measurement equipped with nuclear track detector (CR-39) and electretis considered in this work. Electret is electrostatic analogous of permanent magnet which preserves constant and strong electric field for long time period. Electrets were used to attract radon progeny formed in a cup where CR-39 was placed for radon measurements. In this way the sensitivity of detector could be increased by bringing progeny just in front of detector in more convenient measuring geometry.
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Sensitivity of LR115 detector in Diffusion Chamber to 222Rn in the presence of 220Rn.
Applied Radiation and Isotopes, 2002Co-Authors: J.p.y. Ho, Dragoslav Nikezic, K N YuAbstract:Abstract Determination has been made of the sensitivity of LR115 type 2-track detectors (in units of m) to 222Rn, measured in the presence of 220Rn. Measurements have been made by means of a widely used Diffusion Chamber while Monte Carlo simulations have also been conducted. The experimentally derived sensitivities for 222Rn and 220Rn were found to be 0.470±0.022 and 0.486±0.042 m, respectively. For Monte Carlo simulations, the sensitivities to 222Rn gas were found to range from 0.618×10–2 m (assuming that all 218Po progeny decay before deposition onto the internal walls of the Diffusion Chamber) to 0.405×10–2 m (assuming that all 218Po progeny are deposited on the internal walls of the same containment vessel before decaying). The sensitivity to 220Rn gas of 0.465×10–2 m found from Monte Carlo simulations agrees to within uncertainty with experimental findings. The experimentally derived sensitivity value for 222Rn indicates that 30% of the 218Po progeny decay before deposition onto the internal walls of the Diffusion Chamber.
D Nikezic - One of the best experts on this subject based on the ideXlab platform.
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sensitivity of lr 115 ssntd in a Diffusion Chamber
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2007Co-Authors: S Y Y Leung, D Nikezic, J K C Leung, K N YuAbstract:Abstract Solid-state nuclear track detectors (SSNTDs), such as LR 115, have been commonly used in Diffusion Chambers for long-term measurements of radon gas concentrations. For the LR 115 SSNTD, it has been found that the active layer removed during chemical etching is significantly affected by the presence and amount of stirring, and thus cannot be controlled easily. However, the sensitivity of the LR 115 detector inside a Diffusion Chamber to the radon and/or thoron gas concentration is dependent on the actual removed active layer thickness. This relationship is dependant on the geometry of the Diffusion Chamber and the deposition fraction of 218Po in the Diffusion Chamber, as well as the V function for the LR 115 detector (V is the ratio between the track etch velocity Vt to the bulk etch velocity Vb). This paper presents the experimentally determined relationships between the sensitivity of the LR 115 detector inside a Karlsruhe Diffusion Chamber and the removed active layer thickness, for both radon and thoron. A V function was adjusted to simulate the relationships. In particular, for the case of 222Rn, we have found f ∼ 0.5, where f is the fraction of 218Po which decays inside the Diffusion Chamber before deposition onto available inner surfaces of the Chamber. In conclusion, we have found that the sensitivities critically depend on the actual removed active layer thickness, so this should be monitored and used in determining the sensitivities.
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derivation of v function for lr 115 ssntd from its sensitivity to 220rn in a Diffusion Chamber
Applied Radiation and Isotopes, 2007Co-Authors: S Y Y Leung, D Nikezic, J K C Leung, K N YuAbstract:Abstract The sensitivity of the LR 115 detector inside a Diffusion Chamber to 220Rn gas concentration is dependent on the removed active layer thickness during chemical etching. This dependence is related to the V function for the LR 115 detector (where V is the ratio between the track etch velocity Vt and the bulk etch velocity Vb) and the geometry of the Diffusion Chamber. The present paper presents the experimentally determined relationship between the sensitivity of the LR 115 detector inside a Karlsruhe Diffusion Chamber (determined from the number of etched tracks completely penetrating the active cellulose nitrate layer) and the removed active layer thickness. These data were used to derive the V function for the LR 115 detector, which took the functional form of the Durrani–Green's function, i.e., V = 1 + ( a 1 e - a 2 R + a 3 e - a 4 R ) ( 1 - e - a 5 R ) , with the best-fitted constants as a 1 = 14.50 , a 2 = 0.50 , a 3 = 3.9 and a 4 = 0.066 .
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behavior of 220rn progeny in Diffusion Chamber
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2007Co-Authors: D Nikezic, N StevanovicAbstract:Abstract The distribution of 220Rn (thoron) within the cylindrical Diffusion Chamber decreases exponentially with the distance from the entry filter. The first 220Rn progeny 216Po follows its parent due to its very short half life. Other 220Rn progeny are almost completely deposited, but the deposition is not uniform. Deposition occurs on all internal surfaces of cylinder including vertical wall as well as its bases. Deposition on the upper and lower base is enhanced in the middle and drops toward to the end while the deposition on “vertical” wall is larger closer to the entry membrane.
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radon progeny behavior in Diffusion Chamber
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2005Co-Authors: D Nikezic, N StevanovicAbstract:Abstract The behavior of short-lived radon progeny in a Diffusion Chamber was modeled based on the random Brownian motion and Diffusion. The modeling enables calculations of the fraction of radon progeny that decays in air, as well as, the distribution of the atoms deposited onto the inner walls of the Diffusion Chamber. Up to 23% of 218Po decays in air, while 214Pb and 214Bi are almost fully deposited before decaying. The distribution of deposited progeny was found to be non-uniform. In the second part of the paper, deposition of charged progeny atoms was also considered. The influence of non-uniform deposition of radon progeny on the total sensitivity was investigated for an LR 115 detector in one typical Diffusion Chamber. The electric charge increases the deposition of radon progeny.
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experimental study of track density distribution on lr115 detector and deposition fraction of 218po in Diffusion Chamber
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2002Co-Authors: J.p.y. Ho, D Nikezic, K N YuAbstract:Abstract The radial distribution of track density on a solid-state nuclear track detector inside a Diffusion Chamber is a function of the fraction f of 218 Po decay before deposition. In the present work, procedures are proposed to determine f experimentally by determining the track density distribution on an LR115 detector in a Diffusion Chamber. First, a relatively tall Diffusion Chamber, with a height of 8 cm, was chosen. After exposure, the LR115 detector was etched. A transparent template with concentric circles was devised to study the radial distribution of sensitivity using an optical microscope. The distributions according to different values of f were also calculated using Monte Carlo simulations. By minimizing the deviations between these Monte Carlo curves and the experimental data, f was found to be 0.4.
Mojca Mally - One of the best experts on this subject based on the ideXlab platform.
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controlled shaping of lipid vesicles in a microfluidic Diffusion Chamber
RSC Advances, 2017Co-Authors: Mojca Mally, Bojan Božic, Vrhovec S Hartman, U Klancnik, Sasa Svetina, Jure DergancAbstract:Synthetic lipid vesicles represent an important model system for studying membrane processes, which often depend on membrane shape, but controlled shaping of vesicles remains a challenging experimental task. Here, we present a novel method for shaping giant lipid vesicles by independently regulating osmotic conditions and the concentration of membrane-shaping molecules, which intercalate into the membrane and drive membrane bending. The method is based on the microfluidic Diffusion Chamber, where the solution around the vesicles can be repeatedly exchanged solely by Diffusion, without any hydrodynamic flow that could deform the membrane. By using lipopolysaccharide (LPS) as a vesicle shape-modifying molecule, we demonstrate controlled and reversible transformations across three shape classes, from invaginated to evaginated vesicles. We show that extensive shape transformations can lead to shapes that are assumed to comprise narrow membrane necks that hinder equilibration of the membrane and the vesicle interior. All the observed shapes are in good agreement with the predictions of the area-difference-elasticity model applied to the vesicles that were denser than their surrounding solution. Our results validate the microfluidic Diffusion Chamber as a universal framework for membrane shaping that could also pave the way towards controlled fabrication of synthetic membranes resembling cell-compartments with large surface-to-volume ratios.
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a microfluidic Diffusion Chamber for reversible environmental changes around flaccid lipid vesicles
Lab on a Chip, 2011Co-Authors: Sasa Vrhovec, Mojca Mally, Blaž Kavcic, Jure DergancAbstract:The reversible environmental changes around flaccid lipid vesicles represent a considerable experimental challenge, particularly because of remarkable softness of flaccid membranes, which can warp irreversibly under the slightest hydrodynamic flow. As a result, we have developed a microfluidic device for the controlled analysis of individual flaccid, giant lipid vesicles in a changing chemical environment. The setup combines the advantages of a flow-free microfluidic Diffusion Chamber and optical tweezers, which are used to load the sample vesicles into the Chamber. After a vesicle is loaded into the Diffusion Chamber, its chemical environment is controllably and reversibly changed solely by means of Diffusion. The Chamber is designed as a 250 micrometres-long and 100 micrometres-wide dead-end microchannel, which extends from a T-junction of the main microchannels. Measurements of the flow-velocity profile in the Chamber show that the flow rate decreases exponentially and scales linearly with the flow rate in the main channel. The characteristic length of the exponential decrease is 15 (1 ± 0.13) micrometres, meaning that a large part of the Diffusion Chamber is effectively flow-free. The Diffusion properties are assessed by monitoring the Diffusion of a dye into the Chamber. It was found that a simple 1D Diffusion model fits well to the experimental data. The time needed for the exchange of solutes in the Chamber is of the order of minutes, depending on the solute's molecular weight. Here, we demonstrate how the Diffusion Chamber can be used for reversible environmental changes around flaccid, giant lipid vesicles and membrane tethers (nanotubes).
H. Lihavainen - One of the best experts on this subject based on the ideXlab platform.
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homogeneous water nucleation in a laminar flow Diffusion Chamber
Journal of Chemical Physics, 2010Co-Authors: Alexandra Manka, H. Lihavainen, David Brus, A P Hyvarinen, Judith Wolk, R StreyAbstract:Homogeneous nucleation rates of water at temperatures between 240 and 270 K were measured in a laminar flow Diffusion Chamber at ambient pressure and helium as carrier gas. Being in the range of 102–106 cm−3 s−1, the experimental results extend the nucleation rate data from literature consistently and fill a pre-existing gap. Using the macroscopic vapor pressure, density, and surface tension for water we calculate the nucleation rates predicted by classic nucleation theory (CNT) and by the empirical correction function of CNT by Wolk and Strey [J. Phys. Chem. B 105, 11683 (2001)]. As in the case of other systems (e.g., alcohols), CNT predicts a stronger temperature dependence than experimentally observed, whereas the agreement with the empirical correction function is good for all data sets. Furthermore, the isothermal nucleation rate curves allow us to determine the experimental critical cluster sizes by use of the nucleation theorem. A comparison with the critical cluster sizes calculated by use of the ...
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homogeneous nucleation rate measurements of 1 butanol in helium a comparative study of a thermal Diffusion cloud Chamber and a laminar flow Diffusion Chamber
Journal of Chemical Physics, 2005Co-Authors: David Brus, A P Hyvarinen, Vladimír Ždímal, H. LihavainenAbstract:Isothermal homogeneous nucleation rates of 1-butanol were measured both in a thermal Diffusion cloud Chamber and in a laminar flow Diffusion Chamber built recently at the Institute of Chemical Process Fundamentals, Academy of Sciences of the Czech Republic, Prague, Czech Republic. The chosen system 1-butanol-helium can be studied reasonably well in both devices, in the overlapping range of temperatures. The results were compared with those found in the literature and those measured by Lihavainen in a laminar flow Diffusion Chamber of a similar design. The same isotherms measured with the thermal Diffusion cloud Chamber occur at highest saturation ratios of the three devices. Isotherms measured with the two laminar flow Diffusion Chambers are reasonably close together; the measurements by Lihavainen occur at lowest saturation ratios. The temperature dependences observed were similar in all three devices. The molecular content of critical clusters was calculated using the nucleation theorem and compared wit...
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homogeneous nucleation of n pentanol in a laminar flow Diffusion Chamber
Journal of Chemical Physics, 2001Co-Authors: H. Lihavainen, Y Viisanen, Markku KulmalaAbstract:Nucleation rate isotherms of n-pentanol were measured in laminar flow Diffusion Chamber. n-pentanol was chosen for nucleating vapor and helium for carrier gas as a part of a world wide joint experiment on homogeneous nucleation. Experimental temperature range was from 260 to 290 K. Experimental nucleation rate range was from 103 to 107 cm−3 s−1. The results were compared to the classical nucleation theory and experimental data found in literature. Experimental results were three orders of magnitude higher than predicted by the theory. The difference was constant over the whole experimental range. The saturation ratio dependency of nucleation rate was well predicted by the theory. The number of molecules in the critical clusters was quite consistent with the theory. The results were in reasonable agreement with data found in literature.
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homogeneous nucleation of n pentanol in a laminar flow Diffusion Chamber
NUCLEATION AND ATMOSPHERIC AEROSOLS 2000: 15th International Conference, 2001Co-Authors: H. Lihavainen, Y Viisanen, Markku KulmalaAbstract:As a contribution to the Joint Experiment on Homogenous Nucleation, a version of a laminar flow Diffusion Chamber was developed for nucleation rate measurements. The design and operational characteristics of the Chamber will be presented. Homogenous nucleation rates of n-pentanol were measured as a function of saturation ratio in the temperature range between 260 K and 290 K. The results were compared to the classical nucleation theory. The experimental results were three orders of magnitudes higher than the theoretical predictions. The difference was almost constant over the whole temperature range. The results were compared with results from other experimental devices, they were in good agreement at lower temperatures.
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Homogenous nucleation of n-butanol in laminar flow Diffusion Chamber
Journal of Aerosol Science, 2000Co-Authors: H. Lihavainen, Y ViisanenAbstract:In this study laminar flow Diffusion Chamber was developed to measure homogeneous nucleation rates as a function of saturation and temperature. n-Butanol was chosen for nucleating vapor because its thermodynamic properties are well known.