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排序方式: 共有433条查询结果,搜索用时 93 毫秒
61.
R. Menes N. Grønbech-Jensen P.A. Pincus 《The European physical journal. E, Soft matter》2000,1(4):345-349
Using both theoretical modeling and computer simulations we study a model system for DNA interactions in the vicinity of charged
membranes. We focus on the polarization of the mobile charges in the membranes due to the nearby charged rods (DNA) and the
resulting screening of their fields and inter-rod interactions. We find, both within a Debye-Hückel model and in Brownian
dynamics simulations, that the confinement of the mobile charges to the surface leads to a qualitative reduction in their
ability to screen the charged rods to the degree that the fields and resulting interactions are not finite-ranged as in systems
including a bulk salt concentration, but rather decay algebraically and the screening effect is more like an effective increase
in the multipole moment of the charged rod.
Received 28 September 1999 相似文献
62.
J. -B. Fournier 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(2):261-272
A phenomenological Landau elasticity for the shape, dilation, and lipid-tilt of bilayer membranes is developed. The shape
mode couples with the sum of the monolayers' tilt, while the dilation mode couples with the difference of the monolayers'
tilts. Interactions among membrane inclusions within regular arrays are discussed. Inclusions modifying the membrane thickness
and/or inducing a tilt-difference due to their convex or concave shape yield a dilation-induced attraction and a tilt-difference-induced
repulsion. The resulting interaction can stabilize 2D crystal phases, with the possible coexistence of different lattice spacings when the dilation-tilt-difference coupling is
large. Inclusions favoring crystals are those with either a long-convex or a short-concave hydrophobic core. Inclusions inducing
a local membrane curvature due to their conical shape repel one another. At short inclusions separations, a tilt comparable
with the inclusion's cone angle develops: it relaxes the membrane curvature and reduces the repulsion. At large separations
the tilt vanishes, whatever the value of the shape-tilt coupling.
Received 23 October 1998 and Received in final form 12 January 1999 相似文献
63.
G.G.M. Coppa A. D'Angola 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,6(4):533-539
The paper deals with the stationary distribution of charged particles moving in a material medium, having scattering and absorption
properties, in which a uniform electric field is present. The purpose of the work is finding analytical solutions in simplified
but physically significant situations and comparing different approximations based on a spherical-harmonics expansion of the
velocity distribution.
Received: 28 July 1998 相似文献
64.
M. Dudzinski J. Sznajd J. Zittartz 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(4):575-579
The zero temperature phase diagram of a one-dimensional ferromagnet with cubic single ion anisotropy in an external magnetic
field is studied. The mean-field approximation and the density-matrix renormalization group method are applied. Two phases
at finite magnetic fields are identified: a canted phase with spontaneously broken symmetry and a phase with magnetization
along the magnetic field. Both methods predict that the canted phase exists even for the single-ion anisotropy strong enough
to destroy the magnetic order at zero magnetic field. In contrast to the mean-field theory, the density-matrix renormalization
group predicts a reentrant behavior for the model. The character of the phase transition at finite magnetic field has also
been considered and the critical index has been found.
Received 9 May 2000 and Received in final form 5 July 2000 相似文献
65.
Annett Kreimeyer Franois Andr Catherine Gouyette Tam Huynh-Dinh 《Angewandte Chemie (International ed. in English)》1998,37(20):2853-2855
The uptake of ATP in liposomes was achieved by using the lipophilic derivative cholesteryloxycarbonyl-ATP ( 1 ). Its hydrolysis leading to the release of ATP inside the vesicules (see scheme) was observed with the help of a pH gradient and monitored by 31P NMR spectroscopy. This is the first successful transfer of a nucleoside 5′-triphosphate across a membrane. 相似文献
66.
Maureen M. Tedesco Bereket Ghebremariam Naomi Sakai Stefan Matile 《Angewandte Chemie (International ed. in English)》1999,38(4):540-543
A supramolecular ion channel model mediates transmembrane ion transport (shown schematically) with a selectivity topology similar to that of K+ channels. This supports the biological significance of flexible arene arrays as selective cation binding sites. 相似文献
67.
Intrinsic fluorescent polypyrrole (ppy) nanoparticles with different shapes were fabricated by atmospheric pressure plasma polymerization. Gradient electrical field and polarization of active particles in the plasma induce change of shape of nanoparticles from spherical to rod, when the plasma power varied from 5 W to 10 W. Both X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) results suggest that the atmospheric pressure plasma polymerization process (APPP) at the power of 5 W and 10 W can help to preserve the integrity of the structure of monomer due to the predominant role of radical polymerization in APPP at these powers. However, when the plasma power increased to 20 W, the ring structure of some pyrroles was destroyed, owing to existence of higher energy species. The polypyrrole nanoparticles exhibit the peak fluorescence around 415 nm. Fluorescent results show that the fluorescent properties of polypyrrole nanoparticles are related to the particle size of the polymer. The bigger particles would have more enlarged room for exciton diffusion, resulting in lower fluorescence intensity and red shift of the fluorescent peak. 相似文献
68.
The role of water’s H-bond percolation network in acid-assisted proton transfer was studied in water and glycerol solutions
and in sugar glasses. Proton transfer rates were determined by the fluorescence of pyrene-1-carboxylate, a compound with a
higher pK in its excited state relative to the ground state. Excitation of pyrene-1-COO− produces fluorescence from pyrene-1-COOH when a proton is accepted during the excited singlet state lifetime of pyrene-1-COO−. The presence of glycerol as an aqueous cosolvent decreases proton transfer rates from phosphoric and acetic acid in a manner
that does not follow the Stokes relationship on viscosity. In sugar glass composed of trehalose and sucrose, proton transfer
occurs when phosphate is incorporated in the glass. Sugar glass containing phosphate retains water and it is suggested that
proton transfer requires this water. The infrared (IR) frequency of water bending mode in sugar glass and in aqueous solution
is affected by the presence of phosphate and the IR spectral bands of all phosphate species in water are temperature dependent;
both results are consistent with H-bonding between water and phosphate. The fluorescence results, which studied the effect
of cosolvent, highlight the role of water in assisting proton transfer in reactions involving biological acids, and the IR
results, which give spectroscopic evidence for H-bonding between water and phosphate, are consistent with a mechanism of proton
transfer involving H-bonding. The possibility that the phosphate-rich surface of membranes assists in proton equilibration
in cells is discussed. 相似文献
69.
H. Nowakowska M. Jasiński J. Mizeraczyk 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,54(2):511-518
We present results from simulations of 2D distributions of the electromagnetic field inside a waveguide-based axial-type microwave
plasma source (MPS) used for hydrogen production via methane reforming. The studies are aimed at optimization of discharge
processes and hydrogen production. We derive equations for determining electromagnetic field distributions and next determine
the electromagnetic field distributions for two cases – without and with plasma inside the MPS. For the first case, we examine
the influence of the length of the inner conductor of the coaxial line on electromagnetic field distributions. We have obtained
standing wave patterns along the coaxial line and found resonances for certain positions of the coaxial line inner conductor.
For the case with plasma inside the MPS, we perform calculations assuming that distributions of plasma parameters are known.
Simulations are done for several values of maximum electron density. We have found that for values of electron density greater
than strong skin effect in the plasma is observed. Consequently, plasma may be treated as an extension of the inner conductor
of the coaxial line. We have used FlexPDE software for the calculations. 相似文献
70.
M. Jasiński M. Dors J. Mizeraczyk 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,54(2):179-183
In this paper, results of hydrogen production via methane pyrolysis in the atmospheric pressure microwave plasma with CH4 swirl are presented. A waveguide-based nozzleless cylinder-type microwave plasma source (MPS) was used to convert methane
into hydrogen. The plasma generation was stabilized by a CH4 swirl having a flow rate of 87.5 L min-1. The absorbed microwave power was 1.5–5 kW. The hydrogen production rate and the corresponding energy efficiency were 866 g
(H2) h-1 and 577 g (H2) kWh-1 of microwave energy absorbed by the plasma, respectively. These parameters are better than our previous results when nitrogen
was used as a swirl gas and much better than those typical for other plasma methods of hydrogen production (electron beam,
gliding arc, plasmatron). 相似文献