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Search Results: 1 - 10 of 78 matches for " Primoz Peterlin "
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Using R for data analysis and graphing in an introductory physics laboratory
Primoz Peterlin
Physics , 2009,
Abstract: R is a language and computing environment that has been developed for data manipulation, statistical computing, and scientific graphing. In the paper, we demonstrate its use analyzing data collected in a few experiments taken from an introductory physics laboratory. The examples include a linear dependence, a non-linear dependence, and a histogram. The merits of R are discussed against three options often used for data analysis and graphing: manual graphing using grid paper, general purpose spreadsheet software, and specialized scientific graphing software.
Data analysis and graphing in an introductory physics laboratory: spreadsheet versus statistics suite
Primoz Peterlin
Physics , 2010, DOI: 10.1088/0143-0807/31/4/021
Abstract: Two methods of data analysis are compared: spreadsheet software and a statistics software suite. Their use is compared analyzing data collected in three selected experiments taken from an introductory physics laboratory, which include a linear dependence, a non-linear dependence, and a histogram. The merits of each method are compared.
Frequency-dependent electrodeformation of giant phospholipid vesicles in AC electric field
Primoz Peterlin
Physics , 2010, DOI: 10.1007/s10867-010-9187-3
Abstract: A model of vesicle electrodeformation is described which obtains a parametrized vesicle shape by minimizing the sum of the membrane bending energy and the energy due to the electric field. Both the vesicle membrane and the aqueous media inside and outside the vesicle are treated as leaky dielectrics, and the vesicle itself is modelled as a nearly spherical shape enclosed within a thin membrane. It is demonstrated (a) that the model achieves a good quantitative agreement with the experimentally determined prolate-to-oblate transition frequencies in the kHz range, and (b) that the model can explain a phase diagram of shapes of giant phospholipid vesicles with respect to two parameters: the frequency of the applied AC electric field and the ratio of the electrical conductivities of the aqueous media inside and outside the vesicle, explored in a recent paper (S. Aranda et al., Biophys. J. 95:L19--L21, 2008). A possible use of the frequency-dependent shape transitions of phospholipid vesicles in conductometry of microliter samples is discussed.
Electroformation in a flow chamber with solution exchange as a means of preparation of flaccid giant vesicles
Primoz Peterlin,Vesna Arrigler
Physics , 2007, DOI: 10.1016/j.colsurfb.2008.01.004
Abstract: A recently described technique (Estes and Mayer, Biochim. Biophys. Acta 1712 (2005) 152--160) for the preparation of giant unilamellar vesicles (GUVs) in solutions with high ionic strength is examined. By observing a series of osmotic swellings followed by vesicle bursts upon a micropipette transfer of a single POPC GUV from a sucrose solution into an isoosmolar glycerol solution, a value for the permeability of POPC membrane for glycerol, P = (2.09+/-0.82) x 10^{-8} m/s, has been obtained. Based on this result, an alternative mechanism is proposed for the observed exchange of vesicle interior. With modifications, the method of Estes and Mayer is then applied to preparation of flaccid GUVs.
Determining membrane permeability of giant phospholipid vesicles from a series of videomicroscopy images
Primoz Peterlin,Gasper Jaklic,Tomaz Pisanski
Physics , 2008, DOI: 10.1088/0957-0233/20/5/055801
Abstract: A technique for determining the permeability of a phospholipid membrane on a single giant unilamellar vesicle (GUV) is described, which complements the existing methods utilizing either a planar black lipid membrane or sub-micrometre-sized liposomes. A single GUV is transferred using a micropipette from a solution of a nonpermeable solute into an iso-osmolar solution of a solute with a higher membrane permeability. Osmotical swelling of the vesicle is monitored with a CCD camera mounted on a phase contrast microscope, and a sequence of images is obtained. On each image, the points on the vesicle contour are determined using Sobel filtering with adaptive binarization threshold, and from these, the vesicle radius is calculated with a great accuracy. From the time-dependence of the vesicle radius, the membrane permeability is obtained. Using a test set of data, the method provided a consistent estimate of the POPC membrane permeability for glycerol, P = 1.7 x 10^-8 m/s, with individual samples ranging from 1.61 x 10^-8 m/s to 1.98 x 10^-8 m/s. This value is ~40% lower than the one obtained on similar systems. Possible causes for this discrepancy are discussed.
The prolate-to-oblate shape transition of phospholipid vesicles in response to frequency variation of an AC electric field can be explained by the dielectric anisotropy of a phospholipid bilayer
Primoz Peterlin,Sasa Svetina,Bostjan Zeks
Physics , 2006, DOI: 10.1088/0953-8984/19/13/136220
Abstract: The external electric field deforms flaccid phospholipid vesicles into spheroidal bodies, with the rotational axis aligned with its direction. Deformation is frequency dependent: in the low frequency range (~ 1 kHz), the deformation is typically prolate, while increasing the frequency to the 10 kHz range changes the deformation to oblate. We attempt to explain this behaviour with a theoretical model, based on the minimization of the total free energy of the vesicle. The energy terms taken into account include the membrane bending energy and the energy of the electric field. The latter is calculated from the electric field via the Maxwell stress tensor, where the membrane is modelled as anisotropic lossy dielectric. Vesicle deformation in response to varying frequency is calculated numerically. Using a series expansion, we also derive a simplified expression for the deformation, which retains the frequency dependence of the exact expression and may provide a better substitute for the series expansion used by Winterhalter and Helfrich, which was found to be valid only in the limit of low frequencies. The model with the anisotropic membrane permittivity imposes two constraints on the values of material constants: tangential component of dielectric permittivity tensor of the phospholipid membrane must exceed its radial component by approximately a factor of 3; and the membrane conductivity has to be relatively high, approximately one tenth of the conductivity of the external aqueous medium.
Law of corresponding states for osmotic swelling of vesicles
Primoz Peterlin,Vesna Arrigler,Emir Haleva,Haim Diamant
Physics , 2011, DOI: 10.1039/C1SM06670F
Abstract: As solute molecules permeate into a vesicle due to a concentration difference across its membrane, the vesicle swells through osmosis. The swelling can be divided into two stages: (a) an "ironing" stage, where the volume-to-area ratio of the vesicle increases without a significant change in its area; (b) a stretching stage, where the vesicle grows while remaining essentially spherical, until it ruptures. We show that the crossover between these two stages can be represented as a broadened continuous phase transition. Consequently, the swelling curves for different vesicles and different permeating solutes can be rescaled into a single, theoretically predicted, universal curve. Such a data collapse is demonstrated for giant unilamellar POPC vesicles, osmotically swollen due to the permeation of urea, glycerol, or ethylene glycol. We thereby gain a sensitive measurement of the solutes' membrane permeability coefficients, finding a concentration-independent coefficient for urea, while those of glycerol and ethylene glycol are found to increase with solute concentration. In addition, we use the width of the transition, as extracted from the data collapse, to infer the number of independent bending modes that affect the thermodynamics of the vesicle in the transition region.
Permeability of phospholipid membrane for small polar molecules determined from osmotic swelling of giant phospholipid vesicles
Primoz Peterlin,Vesna Arrigler,Haim Diamant,Emir Haleva
Physics , 2012, DOI: 10.1016/B978-0-12-396534-9.00010-6
Abstract: A method for determining permeability of phospholipid bilayer based on the osmotic swelling of micrometer-sized giant unilamellar vesicles (GUVs) is presented as an alternative to the two established techniques, dynamic light scattering on liposome suspension, and electrical measurements on planar lipid bilayers. In the described technique, an individual GUV is transferred using a micropipette from a sucrose/glucose solution into an isomolar solution containing the solute under investigation. Throughout the experiment, vesicle cross-section is monitored and recorded using a digital camera mounted on a phase-contrast microscope. Using a least-squares procedure for circle fitting, vesicle radius R is computed from the recorded images of vesicle cross-section. Two methods for determining membrane permeability from the obtained R(t) dependence are described: the first one uses the slope of R(t) for a spherical GUV, and the second one the R(t) dependence around the transition point at which a flaccid vesicle transforms into a spherical one. We demonstrate that both methods give consistent estimates for membrane permeability.
Growth and shape transformations of giant phospholipid vesicles upon interaction with an aqueous oleic acid suspension
Primoz Peterlin,Vesna Arrigler,Ksenija Kogej,Sasa Svetina,Peter Walde
Physics , 2009, DOI: 10.1016/j.chemphyslip.2009.03.005
Abstract: The interaction of two types of vesicle systems was investigated: micrometer-sized, giant unilamellar vesicles (GUVs) formed from 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and submicrometer-sized, large unilamellar vesicles (LUVs) formed from oleic acid and oleate, both in a buffered aqueous solution (pH=8.8). Individual POPC GUVs were transferred with a micropipette into a suspension of oleic acid/oleate LUVs, and the shape changes of the GUVs were monitored using optical microscopy. The behavior of POPC GUVs upon transfer into a 0.8 mM suspension of oleic acid, in which oleic acid/oleate forms vesicular bilayer structures, was qualitatively different from the behavior upon transfer into a 0.3 mM suspension of oleic acid/oleate, in which oleic acid/oleate is predominantly present in the form of monomers and possibly non-vesicular aggregates. In both cases, changes in vesicle morphology were observed within tens of seconds after the transfer. Vesicle initially started to evaginate. In 60% of the cases of transfer into a 0.8 mM oleic acid suspension, the evagination process reversed and proceeded to the point where the membrane formed invaginations. In some of these cases, several consecutive transitions between invaginated and evaginated shapes were observed. In the remaining 40% of the cases of transfer into the 0.8 mM oleic acid uspension and in all cases of vesicle transfer into the 0.3 mM oleic acid suspension, no invaginations nor subsequent evaginations were observed. An interpretation of the observed vesicle shape transformation on the basis of the bilayer-couple model is proposed, which takes into account uptake of oleic acid/oleate molecules by the POPC vesicles, oleic acid flip-flop processes and transient pore formation.
Stomach, Hands, Legs, Feet, Eyes, Ears, Mouth, Upper and Lower Teeth, Molars, Eyebrows and Head: The Unity of Christians and the Ancient Topos of Body and Members
Davorin Peterlin
Kairos : Evangelical Journal of Theology , 2010,
Abstract: This article stems from the question of the source from which the Christian author Paul took the image of the body and its members and its head. This image appears in several forms in Paul’s first letter to the Corinthians as well as in Romans, Colossians and Ephesians. The author asks how Paul used it when addressing the issue of the relationships among believers in the church as well as the relationship between the church and Christ. The author maintains that Paul adopted and adapted the ancient topos of the body and its members which appears in many authors from Classical and Hellenistic times, as in Stoic texts of Paul’s era. The key texts are reproduced in Croatian translation. Against these sources the author investigates how Clement of Rome used the same topos. The author concludes that ancient writers adjusted the topos to the aims of their texts and messages. The same applies to the aforementioned hristian writers. Of the two, Paul adapted and developed (more thoroughly than did Clement) the ancient topos to the Christian teaching about the church, and filled it with theological meaning.
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