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.     

Staffing Rosters with Breaks — A Case Study

A complex manual rostering system for directory assistance, telephone operators has been rationalized and the technique of integer programming used to automatically generate staff rosters. These rosters can be generated by relatively unskilled clerical staff. They result in operator costs comparable to manually generated rosters and can be produced in a fraction of the time taken to produce their manual counterparts. Implementation is reported.     

Planetenbewegungen des Flaggenraumes

In [8] the author gave a report on some properties of flag space motions, especially of the composition of screw motions or rotations in flag space. Planet motions more generally are motions which can be composed by two one-parameter-groups. These motions are investigated with respect to their orbits, their multiple ways of construction and the tubular surfaces they can determine. Some of them yield tubular screw surfaces, some others move every sphere the way that it again envellopes a sphere. These motions, which have no Euclidean counterpart, determine non-trivial, kinematically generated LIE-transformations in flag space.     

原子吸收法在有机分析中的应用（Ⅵ）香烟中氢氰酸的分析

原子吸收法在有机分析中的应用（Ⅵ）香烟中氢氰酸的分析谢志海，郎惠云，高云（西北大学化学系，西安，７１００６９）关键词：氢氰酸，测定，原子吸收光谱香烟中的尼古丁，烟焦油等含氮有机物燃烧后将产生氢氰酸，吸入人体后极为有害。国外在这方面的研究始于七十年代，...     

Practical syntheses of [1,3,5]‐triazine dendritic molecules on solid supports

A practical and divergent synthesis of supported [1,3,5]‐triazine dendritic molecules on Wang resin, PEGA resin, SynPhase? Lanterns, and silica gel is described. The alkylamine linkers used allow derivatization with functionality for both synthetic (e.g., supported reagent and scavenger activity) and chemical biology applications. The use of supported intermediates allows differentiation of symmetric linkers without the need for protecting group chemistry. The synthetic route uses inexpensive, readily available starting materials in a straightforward and scaleable strategy. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2248–2259, 2006     

Sample-path optimization of convex stochastic performance functions

In this paper we propose a method for optimizing convex performance functions in stochastic systems. These functions can include expected performance in static systems and steady-state performance in discrete-event dynamic systems; they may be nonsmooth. The method is closely related to retrospective simulation optimization; it appears to overcome some limitations of stochastic approximation, which is often applied to such problems. We explain the method and give computational results for two classes of problems: tandem production lines with up to 50 machines, and stochastic PERT (Program Evaluation and Review Technique) problems with up to 70 nodes and 110 arcs. Sponsored by the National Science Foundation under grant number CCR-9109345, by the Air Force Systems Command, USAF, under grant numbers F49620-93-1-0068 and F49620-95-1-0222, by the U.S. Army Research Office under grant number DAAL03-92-G-0408, and by the U.S. Army Space and Strategic Defense Command under contract number DASG60-91-C-0144. The U.S. Government has certain rights in this material, and is authorized to reproduce and distribute reprints for Governmental purposes notwithstanding any copyright notation thereon. Sponsored by a Wisconsin/Hilldale Research Award, by the U.S. Army Space and Strategic Defense Command under contract number DASG60-91-C-0144, and the Air Force Systems Command, USAF, under grant number F49620-93-1-0068. Sponsored by the National Science Foundation under grant number DDM-9201813.