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  • 1
    Language: English
    In: Biophysical Journal, 1981, Vol.33(2), pp.149-166
    Description: A statistical mechanical model of a bilayer of dipalmitoyl-3-sn-phosphatidylcholine molecules in equilibrium with an aqueous phase saturated with an n-alkane is presented. A mean-field approach developed in previous work on a solventless bilayer (Gruen, Biochim. Biophys. Acta. 595:161--183, 1980) is extended to allow alkane chains to exist in the hydrophobic core of the membrane. As the alkane chains are chemically similar to the lipid chains, much of the analysis follows directly from the solventless model. Novel features of the present model are the inclusion of (a) a term which models the free energy cost of creating space for alkane conformations, (b) a term which constrains the chains to pack evenly in the hydrophobic region of the membrane, and (c) a term which estimates the free energy of mixing of the lipid and alkane molecules in the plane of the bilayer. On uptake of alkane, the dimensions of the bilayer increase. Allowance is made for an increase in thickness and/or an increase in area per lipid. A thermodynamic framework is established which allows evaluation of the free energy of a bilayer of arbitrary dimensions with a view to predicting the equilibrium structure.
    Keywords: Biology
    ISSN: 0006-3495
    E-ISSN: 1542-0086
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  • 2
    Language: English
    In: Biophysical Journal, 1982, Vol.38(3), pp.251-258
    Description: Because a black lipid membrane is compressible, there will be spontaneous fluctuations in its thickness. Qualitative arguments are given that the preferred configuration of the membranes is flat and that thickness fluctuations are smaller in amplitude than the differences in mean thickness observed using different hydrocarbon solvents. Fluctuations with short characteristic lengths will not be large as a result of the large amounts of oil-water contact these would entail. Quantitative analysis based on an extension of the treatment for soap films, predicts that the root mean square (rms) amplitude for fluctuations of wavelength longer than approximately 10 nm is negligible for glyceryl monooleate membranes with squalene (less than 3%) but may be approximately 20% with n-decane. rms fluctuations of 20% would lead to a discrepancy between the rms thickness of the core and the mean reciprocal thickness of only 6%.
    Keywords: Biology
    ISSN: 0006-3495
    E-ISSN: 1542-0086
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  • 3
    Language: English
    In: Biophysical Journal, 1980, Vol.30(1), pp.129-136
    Description: Thermodynamic considerations show that the adsorption of nonpolar molecules into lipid bilayer membranes should depend upon the curvature of the membranes. Estimations of the differences in adsorption of a small n-alkane between a planar phospholipid bilayer and liposomal vesicles have been attempted. For spherical multilamellar liposomes exposed to saturated solutions of alkane in water the adsorption is calculated to be 17–65% of the value for the planar bilayer, depending on the assumptions in the model.
    Keywords: Biology
    ISSN: 0006-3495
    E-ISSN: 1542-0086
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  • 4
    Language: English
    In: Biophysical Journal, 1981, Vol.33(2), pp.167-187
    Description: Equilibrium properties of a model lipid bilayer saturated with an n-alkane are presented. The model exhibits a cut-off in absorption as the chain length of the alkane increases which is similar to that observed with black lipid films. The reasons for this cut-off are explored in detail. The model provides qualitative agreement with the experimental enthalpies of transfer of the various alkanes from bulk pure liquid to the bilayer, and with results of electrical compression experiments on black films. Distributions of alkane across the bilayer for different volume fractions in the membrane are presented. For small volume fractions of alkane, its distribution is fairly even across the bilayer and the alkane chains line up essentially parallel to the lipid chains. For larger volume fractions, the alkane distribution is strongly peaked in the center of the membrane. The alkane chains in the outer regions of the membrane line up essentially parallel to the lipid chains, while those in the center are almost completely disordered. The model suggests that the chains (both lipid and alkane) are in an essentially liquid state with no well defined interface between opposing monolayers. It gives a possible explanation for the discrepancy between the experimental free energy of thinning of some lipid membranes formed from the longer chain length alkanes and the theoretical values estimated from Lifshitz's theory.
    Keywords: Biology
    ISSN: 0006-3495
    E-ISSN: 1542-0086
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  • 5
    Language: English
    In: Astronomy and Computing, July 2016, Vol.16, pp.99-108
    Description: We have developed a crowdsourcing web application for image quality control employed by the Dark Energy Survey. Dubbed the “DES exposure checker”, it renders science-grade images directly to a web browser and allows users to mark problematic features from a set of predefined classes. Users can also generate custom labels and thus help identify previously unknown problem classes. User reports are fed back to hardware and software experts to help mitigate and eliminate recognized issues. We report on the implementation of the application and our experience with its over 100 users, the majority of which are professional or prospective astronomers but not data management experts. We discuss aspects of user training and engagement, and demonstrate how problem reports have been pivotal to rapidly correct artifacts which would likely have been too subtle or infrequent to be recognized otherwise. We conclude with a number of important lessons learned, suggest possible improvements, and recommend this collective exploratory approach for future astronomical surveys or other extensive data sets with a sufficiently large user base. We also release open-source code of the web application and host an online demo version at .
    Keywords: Surveys ; Information Systems: Crowdsourcing ; Human-Centered Computing: Collaborative Filtering ; Astronomy & Astrophysics
    ISSN: 2213-1337
    E-ISSN: 2213-1345
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  • 6
    Language: English
    In: Advances in Space Research, 1996, Vol.17(12), pp.137-140
    Description: We present the description of a design for a proposed Dust Flux Analyser for the Rosetta cometary mission. A concept first developed for the NASA/ESA Tempel II Rendezvous and Halley Intercept Mission /1/, the instrument is able to measure dust particle parameters and fluxes over a velocity range typical of emission from cometary surfaces. It would be mounted on the Rosetta Orbiter and would measure the variation in flux rate throughout all mission phases at the comet. The instrument would measure particle flux, velocity, momentum and density, shape and scattering properties.
    Keywords: Engineering ; Astronomy & Astrophysics ; Physics
    ISSN: 0273-1177
    E-ISSN: 1879-1948
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  • 7
    Language: English
    In: Inorg. Chem.; (United States), 01 April 1976, Vol.15:4
    Description: Three types of infrared studies were performed on the products of condensation of Nb and N/sub 2/ in Ar matrices at 14 K: the behavior of the peaks upon annealing, the dependence of the absorbance upon the N/sub 2/:Ar ratio, and the frequencies of mixed isotope peaks. After extensive variation of experimental parameters, no explanation for the unexpected and rich spectrum could be given. The indications of the experimental results were discussed. (DDA)
    Keywords: Inorganic, Organic, Physical And Analytical Chemistry ; Niobium Complexes ; Structural Chemical Analysis ; Nitrogen 15 ; Isotope Effects ; Nitrogen Complexes ; Annealing ; Argon ; Infrared Spectra ; Matrix Elements ; Complexes ; Elements ; Heat Treatments ; Isotopes ; Light Nuclei ; Nitrogen Isotopes ; Nonmetals ; Nuclei ; Odd-Even Nuclei ; Rare Gases ; Spectra ; Stable Isotopes ; Transition Element Complexes ; 400201 - Chemical & Physicochemical Properties
    ISSN: 00201669
    E-ISSN: 1520510X
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  • 8
    Language: English
    In: Appl. Spectrosc., v. 28, no. 1, pp. 34-38, 01 January 1974
    Description: The application of the matrix isolation technique to the study of the sputtering process is reported. Equations are derived which relate the experimentally measured absorbance data to the sputtering yield. These equations are applied to data from the sputtering of Nb metal by 50 keV rare gas ions. Relative sputtering yields obtained in this manner are in good agreement with sputtering yields obtained by weight loss measurements. The potential of the technique for studies of both physical and chemical sputtering and for the determination of oscillator strengths is discussed.
    Keywords: N60100 -Physics (Atomic & Molecular)-Atomic, Electron, Ion & Molecular Beams & Reactions ; N50200 -Metals, Ceramics, & Other Materials-Metals & Alloys ; Argon Ions- Collisions ; Helium Ions- Collisions ; Krypton Ions- Collisions ; Neon Ions- Collisions ; Niobium- Sputtering ; Sputtering ; Xenon Ions- Collisions ; Absorption Spectra ; Kev Range 10-100 ; Oscillator Strengths
    ISSN: 00037028
    E-ISSN: 19433530
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