排序方式: 共有34条查询结果,搜索用时 0 毫秒
1.
2.
Membrane fusion and aggregation of phospholipid vesicles are reviewed and discussed. The fusion process is viewed as consisting of several stages: aggregation and close apposition of the particles, destabilization, and finally, merging of the bilayers. A procedure is presented which yields both the rate constant of the dimerization (C11) and the rate constant for fusion of the dimers (f11), which is a direct measure of the probability that two apposed vesicles will fuse. Experimental methods used in the study of membrane fusion are reviewed, primarily with respect to their capacity to monitor the kinetics of vesicle fusion. A few kinetic studies on the mixing of aqueous contents, leakage and increase in size of fusing vesicles are presented in detail.The range of C11 values for Ca2+-induced aggregation and fusion of small unilamellar vesicles (SUV, ~ 125 Å radius) composed of phosphatidylserine (PS) is 106 to 5 × 107 M-1 in the presence of Ca2+ concentrations from 1.15 to 2 mM, respectively. For larger PS vesicles (LUV, ~ 500 Å radius) C11 = 6.5 × 107 M-1s-1 in the presence of 5 mM Ca2+. These values are in good agreement with theoretical calculations based on van der Waals and electrostatic interactions, in which binding of cations is explicitly taken into account. The rate constants of fusion, f11, are 5 s-1 for PS SUV and 0.08 s-1 for LUV in the presence of 2 mM and 5 mM Ca2+, respectively. The significance of these fusion rate constants to the duration of the fusion event is discussed.Factors affecting fusion such as cations, temperature, membrane composition vesicle concentration and size are reviewed and analyzed. Di- or tri-valent cations induce fusion of acidic phospholipid vesicles (except for phosphatidylinositol) in either pure or mixed form. Among the neutral phospholipids, phosphatidylcholine (PC) inhibits but phosphatidylethanolamine (PE) sustains or enhances the fusion capacity of acidic phospholipid vesicles. Monovalent cations induce reversible aggregation of negatively charged vesicles, but they inhibit the fusion induced by divalent cations such as Ca2+ or Mg2+. Fusion of neutral phospholipid vesicles, and it occurs the cation-induced fusion of acidic phospholipid vesicles, and it occurs only at temperatures below the gel to liquid crystalline phase transition temperature Tc. This is in contrast to the acidic phospholipid vesicle fusion which is greatly enhanced when the temperature is above the Tc of the phospholipid. 相似文献
3.
G. J. Balster W. van Huffelen H. W. Wilschut D. Chmielewska Z. Sujkowski 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1986,2(1):15-21
KX-ray production cross sections have been measured for beams of14N at 92, 103, 115 and 180 MeV and40Ar at 180 and 300 MeV on targets with atomic numbers ranging from 40 to 90. We find that the measured values can be well reproduced with a plane wave Born calculation, provided that corrections for the Coulomb deflection of the projectile, the increased binding energy of theK-shell electron and relativistic effects of theK-shell wave function are taken properly into account. 相似文献
4.
F. D. Berg M. Pfeiffer O. Schwalb M. Appenheimer W. Döring M. Franke W. Kühn V. Metag W. Niebur R. Novotny J. Ritman M. Röbig H. Ströher A. Boonstra H. Löhner A. Raschke L. Venema H. W. Wilschut N. Brummund W. Henning S. Hlavac R. Holzmann R. S. Simon 《Zeitschrift für Physik A Hadrons and Nuclei》1990,337(3):351-352
π0 -production probability of (9± 2)· 10? 3 per20Ne+Al reaction has been measured at 350 MeV/u using the Two Arm Photon Spectrometer TAPS. This yield is consistent with an interpolation of published π-production rates in heavy ion collisions. 相似文献
5.
R. Ortega D. d'Enterria G. Martınez D. Baiborodin H. Delagrange J. Dıaz F. Fernández H. Löhner T. Matulewicz R. W. Ostendorf S. Schadmand Y. Schutz P. Tlusty R. Turrisi V. Wagner H. W. Wilschut N. Yahlali 《The European Physical Journal A - Hadrons and Nuclei》2006,28(2):161-171
Measured hard-photon multiplicities from second-chance nucleon-nucleon collisions are used in combination with a kinetic thermal
model to estimate the breakup times of excited nuclear systems produced in nucleus-nucleus reactions at intermediate energies.
The obtained nuclear breakup time for the 129Xe + natSn reaction at 50 A MeV is Δτ ≈ 100-300 fm/c for all reaction centralities. The lifetime of the radiating sources produced in seven other different heavy-ion reactions
studied by the TAPS experiment is consistent with Δτ ≈ 100 fm/c, such relatively long thermal photon emission times do not seemingly support the interpretation of nuclear breakup as due
to a fast spinodal process for the heavy nuclear systems studied. 相似文献
6.
M. Nuñez Portela E. A. Dijck A. Mohanty H. Bekker J. E. van den Berg G. S. Giri S. Hoekstra C. J. G. Onderwater S. Schlesser R. G. E. Timmermans O. O. Versolato L. Willmann H. W. Wilschut K. Jungmann 《Applied physics. B, Lasers and optics》2014,114(1-2):173-182
A single Ra+ ion stored in a Paul radio frequency ion trap has excellent potential for a precision measurement of the electroweak mixing angle at low momentum transfer and as the most stable optical clock. The effective transport and cooling of singly charged ions of the isotopes 209Ra to 214Ra in a gas filled radio frequency quadrupole device is reported. The absolute frequencies of the transition 7s2S1/2–7d2D3/2 at wavelength 828 nm have been determined in 212–214Ra+ with ≤19 MHz uncertainty using laser spectroscopy on small samples of ions trapped in a linear Paul trap at the online facility Trapped Radioactive Isotopes: µicrolaboratories for fundamental Physics (TRIµP) of the Kernfysisch Versneller Instituut. 相似文献
7.
J. Wilczynski J. D. Hinnefeld E. E. Koldenhof H. K. W. Leegte R. H. Siemssen H. W. Wilschut Y. X. Xie 《Physics letters. [Part B]》1989,220(4):497-501
Charged-particle survival fractions of primary projectile-like fragments from the 40Ar + 197Au reaction at 450 MeV were measured by using a large array of 32 phoswich detectors operating in coincidence with a detector of projectile-like fragments. Differential survival fractions of the primary pickup and stripping reaction products indicate a dependence of the average excitation energy generated in the primary fragments on the direction of the mass transfer. 相似文献
8.
9.
F. D. Berg A. Boonstra H. P. Braak N. Brummund W. Döring M. Franke P. Gonthier W. Henning W. T. Hering S. Hlaváč R. Holzmann B. Krusche W. Kühn H. Lohner R. Lorencz V. Metag W. Niebur R. Novotny R. Ostendorf M. Pfeiffer A. Raschke J. Ritman M. Röbig Y. Schutz O. Schwalb R. S. Simon H. Ströher L. Venema H. W. Wilschut 《Zeitschrift für Physik A Hadrons and Nuclei》1991,340(3):297-302
The production of
0 and mesons has been studied in the reactions20Ne +Al at 350 MeV/u and40Ar + Ca at 1.0 GeV/u. Rapidity distributions and transverse momentum spectra have been measured and are compared to thermal distributions.Dedicated to Prof. Dr. P. Kienle on the occasion of his 60th birthday 相似文献
10.
T. Matulewicz L. Aphecetche Y. Charbonnier H. Delagrange K.K. Gudima G. Martınez M. Płoszajczak Y. Schutz V.D. Toneev M. Appenheimer R. Averbeck J. Dıaz A. Döppenschmidt M.J. van Goethem S. Hlavač M. Hoefman R. Holzmann F. Lefèvre A. Kugler H. Löhner A. Marın V. Metag R. Novotny R.W. Ostendorf R.H. Siemssen R.S. Simon R. Stratmann H. Ströher P. Tlusty P.H. Vogt V. Wagner J. Weiss H.W. Wilschut F. Wissmann A.R. Wolf M. Wolf 《The European Physical Journal A - Hadrons and Nuclei》2000,9(1):69-72
Proton-π0 coincidences have been measured at the beam energy of 180A MeV in the reaction Ar+Ca studied by TAPS at SIS/GSI. In the proton-π0 invariant mass spectrum we observe a significant excess of strength above the background obtained by event mixing. We attribute
this signal to the strength distribution N
Δ of the Δ baryonic resonance. No correlation is observed in the case of deuteron-π0 coincidences. Assuming isotropic emission of π0 and Δ+ from a midrapidity thermal source and isospin symmetry, we determined the global N
Δ/N
πratio of 0.79 ±0.30(stat) ±0.2(syst). This value indicates that most pions produced at subthreshold energy in heavy-ion reaction
are mediated by the Δ-resonance.
Received: 7 April 2000 / Accepted: 29 August 2000 相似文献