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  • 1981  (130)
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  • 1981  (130)
  • 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: Journal of Colloid And Interface Science, 1981, Vol.84(1), pp.281-283
    Keywords: Engineering ; Chemistry
    ISSN: 0021-9797
    E-ISSN: 1095-7103
    Source: ScienceDirect Journals (Elsevier)
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  • 3
    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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  • 4
    Language: English
    In: Surface Science, 1981, Vol.106(1), pp.160-164
    Description: Small Particles and Inorganic Clusters [Proc. Conf.], Lausanne, Switzerland, Sept. 1980. Photo-induced diffusion and clustering have been studied for sputtered Ag and Mo atoms in Ar, Kr, and N sub 2 matrices. Absorption of light induces...
    Keywords: Chemistry ; Physics
    ISSN: 0039-6028
    E-ISSN: 1879-2758
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  • 5
    Language: English
    In: The Journal of Chemical Physics, 01 January 1981, Vol.74(1), pp.205-214
    Description: UV‐absorption spectra are reported of neutral atoms and ions of Ti, Zr, and Mo in Ar and Kr matrices. The matrix‐isolated species are produced by ion bombardment of a bulk metal target. Thermal and photoannealing experiments indicate that sputtered neutral atoms may occupy one or two distinct matrix sites, depending on the system. Sputtered ions, after being neutralized in the matrix, either go preferentially into the higher energy site, i.e., the site whose absorption bands are shifted farther to the blue, when atoms already populate two sites, or they create a new site at higher energy when there is only one site for atoms. Deconvolution of matrix isolation spectra into contributions from individual sites shows that spectra due to atoms in a particular site correspond much better to gas phase spectra than do total matrix isolation spectra. Matrix shifts of atomic absorption bands for both sites can be rationalized using a model by McCarty and Robinson if allowance is made for matrix distortion around solute atoms. The blue, or close‐packed, site is found to correspond to a solute atom replacing a single matrix atom without inducing appreciable matrix distortion, whereas the red, or expanded, site requires the cage around a solute atom to be enlarged by a few percent.
    Keywords: Atomic And Molecular Physics ; Molybdenum ; Absorption Spectra ; Ultraviolet Spectra ; Titanium ; Zirconium ; Argon ; Krypton ; Matrix Isolation ; Elements ; Fluids ; Gases ; Metals ; Nonmetals ; Rare Gases ; Refractory Metals ; Spectra ; Transition Elements 640302 -- Atomic, Molecular & Chemical Physics-- Atomic & Molecular Properties & Theory;
    ISSN: 0021-9606
    E-ISSN: 1089-7690
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  • 6
    Language: English
    In: Surface Science, 1981, Vol.110(1), pp.151-178
    Description: In sehr ausfuehrlicher mathematischer Weise wird ueber die theoretische Grundlagen eines mit Laserstrahlanregung arbeitenden Fluoreszenz-Spektroskopieverfahrens (LIF) zur Bestimmung der Geschwindigkeitsverteilung von Zirkoniumatomen berichtet, die sich beim Metalltargetbeschuss mit 1 bis 3 keV in der Edelgasumgebung von Kr(+) und Ar(+) einstellt. Die Anregung erfolgt mit einem abstimmbaren, gepumpten Farblaser. Die Bestimmung der Geschwindigkeitsverteilung erfolgt durch Abtastung der Laserfrequenz durch die Doppler-verschobenen Absorptionsfrequenzen der auftretenden Atome mit einem Laserstrahlnormal der Targetoberflaeche. Zur Beschreibung dieser LIF-Prozesse entwickelte man ein Modell mit 3 Atomenergiebereichen (Wechselwirkung eines Laserstrahls mit bekannter Bandbreite, Strahldichte, Pulsdauer und Strahldurchmesser). Ein weiterer wichtiger Modellparameter war die Uebergangsgeschwindigkeit in diesen Atomenergiebereichen (Fluoreszenzerregung, Emissionsbereiche). Von der Targetkammer wird ein Schnittbild gezeigt. Im LIF-Spektroskopieverfahren bei unterschiedlichen Energiedichten des Anregungslaserstrahls erhaltene Geschwindigkeitsverteilungsergebnisse fasste man in zahlreichen Diagrammen zusammen.
    Keywords: Chemistry ; Physics
    ISSN: 0039-6028
    E-ISSN: 1879-2758
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  • 7
    Language: English
    In: Psychiatry Research, 1981, Vol.4(2), pp.213-228
    Description: The validity and reproducibility of psychiatric diagnosis are crucial to psychiatric research. To establish confidence in assigning schizotypal features, three paradigms estimating the reliability of a new instrument, the Schedule for Schizotypal Personalities (SSP), were tested. The first paradigm considered joint, but independent evaluations made by two raters simultaneously. The second paradigm assessed evaluations on different occasions, with a mean interim time of 5.9 months (test-retest procedure). Both reliability paradigms demonstrated high levels of agreement for all of the scaled items. Ninety percent of the intraclass correlation coefficients were 0.80 or better for the joint evaluations, and 70% were 0.80 or better for the test-retest evaluation. The third paradigm measured the reliability of DSM-III Schizotypal Personality Disorder. The kappa value for measuring diagnostic agreement was 0.88. The authors recommend the use of the SSP as an interview schedule and discuss the implications of their findings for genetic and biological research of schizophrenia spectrum disorders.
    Keywords: Schizotypal Personality Disorder ; Borderline Personality Disorder ; Borderline Schizophrenia ; Schizophrenia Spectrum ; Medicine
    ISSN: 0165-1781
    E-ISSN: 1872-7123
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  • 8
    Language: English
    In: Chemical Physics Letters, 1981, Vol.82(2), pp.315-320
    Description: We have considered variations in dielectric polarization over distances comparable to molecular dimensions in the ice structure and in aqueous media. The decay of polarization away from a surface and the associated “hydration force” have been studied analytically in ice and by molecular dynamics in water.
    Keywords: Chemistry
    ISSN: 0009-2614
    E-ISSN: 1873-4448
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  • 9
    Language: English
    In: The Journal of Chemical Physics, 15 May 1981, Vol.74(10), pp.5547-5557
    Description: The time resolved fluorescence spectra of Mo 2 isolated in Ar and Kr matrices at 14 °K are presented. Depending on excitation wavelength, either of two separate vibrational progressions with 475.7 (±4.5) cm −1 spacings can be observed in emission. Similarities between several features in the two emission spectra lead to the conclusion that the progressions arise from Mo 2 trapped in two distinct sites, each characterized by its own absorption spectrum. Excitation spectra elucidate the overlapping absorption spectra of the two sites. The measured emission lifetimes are long and not single exponential. In krypton matrices, lifetimes of 0.85 msec from one site and a biexponential emission decay of 0.70 and 1.94 msec from a second site are observed. In argon matrices, 2.1 msec emission decay times in one site and a triexponential decay with components of 2.1, 3.93, and 6.3 msec were measured in a second site. Phonon structure in the well resolved spectra show that the matrix coupling is different for the two matrix sites. Various empirical correlation rules are used to test the validity of ω e as well as to compare it to other experimental quantities for Mo 2 . These rules indicate a 1.9 Å bond length for Mo 2 . The fluorescence lifetimes and the large spectral shift of the emission relative to the excitation energy lead to the conclusion that the emission does not emanate from the initially excited level. Instead, the emission appears to come from one of the higher spin multiplicity levels in a dense manifold of states lying at somewhat lower energies than the 1 Σ u + level coupled by laser radiation to the 1 Σ g + ground state.
    ISSN: 0021-9606
    E-ISSN: 1089-7690
    Source: © 1981 American Institute of Physics (AIP)〈img src=http://exlibris-pub.s3.amazonaws.com/AIP_edited.gif style="vertical-align:middle;margin-left:7px"〉
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  • 10
    Language: English
    In: The Journal of Chemical Physics, 01 June 1981, Vol.74(11), pp.6448-6457
    Description: Doppler shift laser induced fluorescence spectroscopy was used to determine the relative sputtering yields and number density velocity distribution of sputtered neutral ground state zirconium atoms. Neither change in primary ion energy over the range 1–3 keV nor change in primary ion mass (Ar + , Kr + ) affected the velocity distribution despite large changes in the sputtering yield. The measured number density velocity distributions n ( v ) are well explained by standard linear collision cascade theory and follow the expression n ( v ) d v  α [ v 2 /( v 2 + v 2 b ) 3 ] d v , where v b is the velocity corresponding to a surface binding energy, E b = 1/2 m Zr v 2 b , with E b = 6.305 eV, the bulk zirconium sublimation energy. Surprisingly, the number density velocity distributions of zirconium atoms sputtered in two excited states ( a   3 F 3,4 ) are indistinquishable from that measured for ground state zirconium atoms. Further, the sputtering yield dependence on primary ion energy for the 3 F 3,4 was also, within experimental error, the same as for the 3 F 2 ground state zirconium. The sputtering yield for the two excited states represents almot 40% of the total yield of zirconium. Evaluation of the results incorporates for the first time the effects of power broadening, transit time broadening, and velocity dependent fluorescent detection efficiencies.
    Keywords: Classical And Quantum Mechanics, General Physics ; Argon Ions ; Collisions ; Krypton Ions ; Zirconium ; Sputtering ; Distribution ; Fluorescence ; Ion Beams ; Kev Range 01-10 ; Surfaces ; Velocity ; Beams ; Charged Particles ; Elements ; Energy Range ; Ions ; Kev Range ; Luminescence ; Metals ; Transition Elements ; 640301 - Atomic, Molecular & Chemical Physics- Beams & Their Reactions;
    ISSN: 0021-9606
    E-ISSN: 1089-7690
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