Determination of the rate of rapid lipid transfer induced by poly(ethylene glycol) using the SLM Fourier transform phase and modulation spectrofluorometer

Rate constants were determined for the transfer of the fluorescent lipid probe 1-palmitoyl-2-[[2-[4-(6-phenyl-trans-1,3,5-hexatrienyl)phenyl]ethyl] oxy]carbonyl]-3-sn-phosphatidylcholine (DPHpPC) between large, unilamellar extrusion vesicles composed either of dipalmitoyl phosphatidylcholine (DPPC) or of DPPC mixed with a small amount (0.5 mol%) of lyso phosphatidylcholine (Lyso PC). Transfer of the lipid probe in the presence of varying concentrations of poly(ethylene glycol) (PEG) was monitored using the SLM 48000-MHF Multi-Harmonic Fourier Transform phase and modulation spectrofluorometer to collect multifrequency phase and modulation fluorescence data sets on a subsecond time scale. The unique ability of this instrument to yield accurate fluorescence lifetime data on this time scale allowed transfer to be detected in terms of a time-dependent change in the fluorescent lifetime distribution associated with the lipid-like DPHpPC probe. This probe demonstrates two short fluoresence decay times (ca. 1.1–1.4 and 4.3–4.8 ns) in a probe-rich environment but a single long lifetime (ca. 7 ns) in a probe-poor environment. A simple two-state model for initial lipid transfer was used to analyze the multifrequency data sets collected over a 4-s time frame to obtain the time rate of change of the concentrations of donor and acceptor probe populations following rapid mixing of vesicles with PEG. The ability to measure fluorescence lifetimes on this time scale has allowed us to show that the of rate of lipid transfer increased dramatically at 35% PEG in both fusing and nonfusing vesicle systems. These results are interpreted in terms of a distinct interbilayer structure associated with intimate bilayer contact induced by high and potentially fusogenic concentrations of PEG.     

Phase behaviour of colloid-polymer mixtures

Summary We review the phase behaviour of mixtures of colloids and non-adsorbing polymers. The exclusion of polymer molecules from overlapping ?depletion zones? between two neighbouring colloidal particles results in an unbalanced osmotic pressure pushing the particles together. This depletion potential is separately tunable in range and depth. Theory predicts that the resulting phase behaviour is sensitive to ξ=r _g/R, the ratio of the radius of gyration of a polymer molecule, to the radius of the colloid. At large ξ, a stable colloidalliquid phase becomes possible. This has been confirmed by recent experiments. The formation of non-equilibrium ?transient gel? states when the size ratio is small (≈0.08) is also introduced briefly. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Holographic image subtraction using a polarization technique

A holographic image subtraction technique is proposed. The vector nature of light is utilized in introducing a phase difference of π between the two reconstructed object waves. The experimental results are also presented.     

Multidimensional intermittency analysis

We propose a method to perform the intermittency analysis of multi hadron production in up to three momentum space dimensions. The analysis of realistic (approximately) selfsimilar cascade models shows that the strongest rise of multiplicity moments with decreasing phase space intervals and the closest approach to a power law occurs in three dimensions. Moments of higher orderF ^(q) are related to the second momentF ⁽²⁾ by a power law in good approximation. These powers are found independent of the dimensions in the models and in available data; furthermore, they are only weakly dependent on the reaction type. The relevance to the quark gluon plasma search is discussed.     

Compactness properties of the integration map for Volterra measures in non-normable spaces

We make a detailed study of the compactness properties of the integration map associated with the classical Volterra (vector valued) measure inX=L ^p([0, 1]), forp in [1, ∞], and inX=C([0, 1]), whereX is equipped with its relevant weak or weak-star topology. The spaceX (a Frechet space) of all complex valued sequences, equipped with the pointwise convergence topology, is also considered.     

Observation of Substitutional Fe in CEMS Measurements on Synthetic CVD Diamond

Hyperfine Interactions - Conversion electron Mössbauer spectroscopy measurements have been made on a diamond sample synthesized by chemical vapour deposition. The sample was implanted with 70...     

Mean-value theorems and the nonoscillatory nature of solutions of partial differential equations in the spaces En and Pn

Analogs of the mean-value theorem are obtained for the Poisson equation with the Laplace-Beltrami operator in Euclidean and spherical spaces.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 44, No. 11, pp. 1477–1483, November, 1992.