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1.
A. V. Gorelov L. N. Vasil’eva A. Du. Chesne E. G. Timoshenko Yu. A. Kuznetsov K. A. Dawson 《Il Nuovo Cimento D》1994,16(7):711-720
Summary We analyse data from the dynamic light scattering of poly(N-isopropylacrilamide) in water solution as we cross the collapse
transition. Experimental data are interpreted by the Gaussian self-consistent Zimm model that takes into account two- and
three-body excluded-volume effects, and Oseen hydrodynamic interactions, as well as by the standard cumulant and Contin analyses.
By fitting the dynamic structure factor we extract the temperature dependence of the diffusion coefficientD and the first relaxation time τ1 across the collapse transition for a range of scattering angles. The relaxation time τ1 possesses a characteristic peak at about 32.4 °C due to slowing of the internal motions of the polymer at the theta-point,
and a minimum at 33.4 °C. We interpret this as a combination of collapse closely followed by the growth of critical correlations.
At large scattering angles we reach the universalk
3 regime, and observe that this behaviour vanishes at the onset of collapse transition.
Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994. 相似文献
2.
The uniform charge distribution inside a nucleus is re-examined by using a diffused charge distribution, which reduces to the uniform charge distribution when the thickness is taken to be zero. Electron radial wave functions and ft values of superallowed Fermi transitions are discussed in terms of these two different charge distributions. 相似文献
3.
The conformational properties of charge-balanced polyampholytes described by the end-to-end distance or radius of gyration depend on parameters such as the temperature and pH as well as on the detailed charge distribution along the backbone. In this work we present a method to determine the charge distribution along a semi-stiff polyampholyte backbone which will result in a thermodynamically stable structure for the compactness of interest, from several loops to an uncoiled structure, performed in a single computer experiment. 相似文献
4.
An iterative procedure is presented for determining a static nuclear charge distribution from experimental electron scattering cross sections and muonie atom X-ray transition energies. The errors and error correlations implied by the independent statistical errors in the experimental data are expressed in coordinate space, and kernels are derived which specify the linear constraints imposed on the charge density by the experimental data. Pseudo-experimental data for 208Pb, generated from a known charge distribution, are used to demonstrate the validity of the procedure. A detailed analysis of experimental data for 208Pb is presented, utilizing electron scattering data at five different energies and six muonic energy levels. The theoretical implications of this work concerning quantum density fluctuations and the possible existence of a central depression are discussed. 相似文献
5.
We have studied the adsorption of neutral polyampholytes on model charged surfaces that have been characterized by contact
angle and streaming current measurements. The loop size distributions of adsorbed polymer chains have been obtained using
atomic-force microscopy (AFM) and compared to recent theoretical predictions. We find a qualitative agreement with theory;
the higher the surface charge, the smaller the number of monomers in the adsorbed layer. We propose an original scenario for
the adsorption of polyampholytes on surfaces covered with both neutral long-chain and charged short-chain thiols.
Received 22 February 2002 and Received in final form 23 April 2002 相似文献
6.
Monte Carlo simulations are used to study the non-uniform equilibrium charge distribution along a single annealed polyelectrolyte
chain under θ solvent conditions and with added salt. Within a range of the order of the Debye length charge accumulates at
chain ends while a slight charge depletion appears in the central part of the chain. The simulation results are compared with
theoretical predictions recently given by Castelnovo et al. In the parameter range where the theory can be applied we find almost perfect quantitative agreement.
Received 7 March 2002 and Received in final form 28 May 2002 相似文献
7.
The space charge accumulation in CdZnTe crystals seriously affects the performance of high-flux pulse detectors.The influence of sub-bandgap illumination on the space charge distribution and device performance in CdZnTe crystals were studied theoretically by Silvaco TCAD software simulation.The sub-bandgap illumination with a wavelength of 890 nm and intensity of 8×10?8 W/cm2 were used in the simulation to explore the space charge distribution and internal electric field distribution in CdZnTe crystals.The simulation results show that the deep level occupation faction is manipulated by the sub-bandgap illumination,thus space charge concentration can be reduced under the bias voltage of 500 V.A flat electric field distribution is obtained,which significantly improves the charge collection efficiency of the CdZnTe detector.Meanwhile,premised on the high resistivity of CdZnTe crystal,the space charge concentration in the crystal can be further reduced with the wavelength of 850 nm and intensity of 1×10?7 W/cm2 illumination.The electric field distribution is flatter and the carrier collection efficiency of the device can be improved more effectively. 相似文献
8.
O.V. Bychuk B. O'Shaughnessy N.J. Turro 《The European physical journal. E, Soft matter》2001,4(3):281-291
We propose and theoretically study an experiment designed to measure short-time polymer reaction kinetics in melts or dilute
solutions. The photolysis of groups centrally located along chain backbones, one group per chain, creates pairs of spatially
highly correlated macroradicals. We calculate time-dependent rate coefficients κ(t) governing their first-order recombination kinetics, which are novel on account of the far-from-equilibrium initial conditions.
In dilute solutions (good solvents) reaction kinetics are intrinsically weak, despite the highly reactive radical groups involved.
This leads to a generalised mean-field kinetics in which the rate of radical density decay - ∼S(t), where S(t) ∼t
- (1 + g/3) is the equilibrium return probability for 2 reactive groups, given initial contact. Here g≈ 0.27 is the correlation hole exponent for self-avoiding chain ends. For times beyond the longest coil relaxation time τ,
- ∼S(t) remains true, but center of gravity coil diffusion takes over with rms displacement of reactive groups x(t) ∼t
1/2 and S(t) ∼ 1/x
3(t). At the shortest times ( t
10-6s), recombination is inhibited due to spin selection rules and we find ∼tS(t). In melts, kinetics are intrinsically diffusion-controlled, leading to entirely different rate laws. During the regime limited
by spin selection rules, the density of radicals decays linearly, n(0) - n(t) ∼t. At longer times the standard result - ∼d
3(t)/d (for randomly distributed ends) is replaced by ∼d2x
3(t)/d
2 for these correlated initial conditions. The long-time behavior, t > τ, has the same scaling form in time as for dilute solutions.
Received 18 May 2000 相似文献
9.
V. Fourmaux-Demange A. Brûlet F. Boué P. Davidson P. Keller J.P. Cotton 《The European physical journal. E, Soft matter》2000,1(4):301-317
We have studied the rheology and the conformation of stretched comb-like liquid-crystalline polymers. Both the influence of
the comb-like structure and the specific effect of the nematic interaction on the dynamics are investigated. For this purpose,
two isomers of a comb-like polymetacrylate polymer, of well-defined molecular weights, were synthesized: one displays a nematic
phase over a wide range of temperature, the other one has only an isotropic phase. Even with high degrees of polymerization
N, between 40 and 1000, the polymer chains studied were not entangled. The stress-strain curves during the stretching and relaxation
processes show differences between the isotropic and nematic comb-like polymers. They suggest that, in the nematic phase,
the chain dynamics is more cooperative than for a usual linear polymer. Small-angle neutron scattering has been used in order
to determine the evolution of the chain conformation after stretching, as a function of the duration of relaxation t
r. The conformation can be described with two parameters only: , the global deformation of the polymer chain, and p, the number of statistical units of locally relaxed sub-chains. For the comb-like polymer, the chain deformation is pseudo-affine:
is always smaller than (the deformation ratio of the whole sample). In the isotropic phase, has a constant value, while pincreases as tr. This latter behavior is not that expected for non-entangled chains, in which p varies as t
r
1/2 (Rouse model). In the nematic phase, decreases as a stretched exponential function of t
r, while p remains constant. The dynamics of the comb-like polymers is discussed in terms of living clusters from which junctions are
produced by interactions between side chains. The nematic interaction increases the lifetime of these junctions and, strikingly,
the relaxation is the same at all scales of the whole polymer chain.
Received 5 May 1999 and Received in final form 18 October 1999 相似文献
10.
F. Pincet S. Cribier E. Perez 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(1):127-130
Many experiments done on neutral lipid bilayers in pure water show weak repulsions. These weak forces prevent vesicles from
adhering and are generally overcome by adding some salt in the aqueous medium. They also appear as stray repulsions in surface
forces measurements made on lipid bilayers. Using a surface forces apparatus in pure water and in salt solution, we have measured
the forces between two stearoyl-oleoyl-phosphatidyl-choline (SOPC) bilayers and between two dimiristoyl-phosphatidyl-ethanolamine
(DMPE) bilayers. The results show that the repulsions are due to a small amount of negative charges coming from impurities
in SOPC. This was quantitatively confirmed by electrophoretic measurements. There are 3 times less charges in the case of
DMPE layers. The effect of these charges which is negligible at high salt concentration may significantly affect the adhesion
energy and behaviour of neutral lipid bilayers between 0 and salt.
Received 18 December 1998 相似文献
11.
Kenneth M. Beck Alan G. Joly Wayne P. Hess 《Applied Physics A: Materials Science & Processing》2010,101(1):61-64
When an ionic metal oxide crystal is cleaved, inhomogeneous electrical charging of the surface can be a result. Such an effect
has been well documented in magnesium oxide (100). For example, recent rigorous AFM studies indicate that nanoscale charged
clusters of MgO are created during cleavage, with high concentrations often located at terrace step edges (Barth and Henry
in J. Phys. Chem. C 113:247, 2009). In addition, ablation processes of freshly cleaved magnesium oxide crystals may be effected by remnant surface charging
and microstructures (Stoneham et al. in Appl. Phys. A 69:S81, 1999). We report here that such surface charging strongly impacts neutral atom desorption, even under conditions of extremely mild excitation of surface terrace features. In our experiments, single-crystal
MgO (100) is cleaved in air and placed in an ultra-high vacuum chamber (UHV). We irradiate the crystal at 6.4 eV, photon energy
resonant with five-coordinated (5-C) terrace sites and probe desorbing neutral oxygen atoms. It is found that a significant
fraction of desorbed neutral oxygen atoms from the charged surface possess kinetic energies in excess of 0.7 eV. This is in
contrast to uncharged samples (discharged in vacuo over 24 hours) that display a near-thermal oxygen atom distribution. 相似文献
12.
13.
A new method is used to analyze recent experiments on electron scattering on 3He in the high momentum transfer region. The accuracy of the new measurements is very high so that the charge density can be determined with much higher accuracy than before. We find that further reduction of the error in charge density can only be achieved by a more accurate measurement of the region 3 < q < 6 fm?1. Continuing the previous work of Hetherington and Borysowicz, a very useful approximate relation is derived between the error of charge density and the error of measurements of form factor. We find that linear expansion methods lead to similar results as the present method. They require, however, stronger asymptotic assumptions about ?(r). 相似文献
14.
A Pd catalyst bearing acetylacetone ligand [(CH3CO)2CHPdCl2] was covalently attracted onto the surface of glass slides, and then these Pd-terminated glass slides were immersed into a toluene solution of norbornene (NB) to produce a vinyl-type addition polynorbornene (PNB) layer on the surface of glass slides. It was found that the contract angles of the PNB-terminated glass slides surface increased with the increasing of polymerization time, and the thickness of the PNB layers were approximately 0-44.0 μm when the polymerization time was 0.5-24 h. The researching on etching also has been operated. 相似文献
15.
We discuss theoretically the relaxation of charge fluctuations in polyampholyte solutions. It has been shown previously by
some of us (J. Wittmer et al. Europhys. Lett. 24, 263 (1993)) that the charge distribution along the polyampholyte backbone has a dramatic influence on the polarization energy
and hence on the solubility. Here it is demonstrated that a similar effect exists for the charge relaxation. The charge relaxation
mechanism qualitatively depends on the statistics: for alternating polyampholytes the relaxation is mainly due to local dipole
inversion and is not primarily driven by electrostatic interactions, whereas for random polyampholytes it is driven by electrostatic
interactions. Intermediate statistics (with short-ranged (exponential) correlations) appear as a combination of these two
limiting cases: short-wavelength modes are insensitive to the loss of correlations along the backbone, whereas long-wavelength
modes correspond to a random statistics with renormalized charges. The relaxation of the dielectric constant is also calculated.
Received: 20 December 2002 / Accepted: 13 March 2003 / Published online: 24 April 2003
RID="a"
ID="a"e-mail: johner@ics.u-strasbg.fr 相似文献
16.
The ion fractions of 5 keV Si+ ions singly scattered from iodine adatoms adsorbed on Al(1 0 0), Si(1 1 1) and pre-oxidized Si(1 1 1) were measured with time-of-flight spectroscopy. A considerable ion yield was observed, which did not change significantly with exit angle or I coverage. The mechanism of ion formation is assigned to valence electron resonant charge transfer (RCT) assisted by promotion of the Si ionization level. The yields are smaller than those of Si scattered from Cs adatoms, however, which suggests that electron tunneling from the occupied chemisorption states of the I adatom provides an additional neutralization channel. 相似文献
17.
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19.
D.J. Hinde A.C. Berriman R.D. Butt M. Dasgupta C.R. Morton A. Mukherjee J.O. Newton 《The European Physical Journal A - Hadrons and Nuclei》2002,13(1-2):149-154
In the fusion of heavy nuclei, there is a distribution of fusion barrier energies resulting from coupling between intrinsic
motion and internal degrees of freedom. Precise experimental measurements of excitation functions have allowed the extraction
of the distributions by taking the second derivative using a point-difference method. In the case of statically deformed nuclei,
experimental data shows that the different fusion barrier energies correspond to different physical configurations of the
colliding nuclei, the latter affecting the subsequent dynamical trajectories over the potential energy surface, influencing
the ultimate reaction products, as for example in quasi-fission. The fusion barrier distribution is also valuable in understanding
the fusion of weakly bound nuclei, enabling a reliable prediction of the expected fusion cross-sections, and thus the determination
of fusion suppression factors at above-barrier energies.
Received: 1 May 2001 / Accepted: 4 December 2001 相似文献
20.
Y. Rouault 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(3):321-324
A living polymer system is used to study the effect of concentration on a broad, polydisperse two-dimensional polymer system.
It is found that the mean squared end-to-end radius of a chain of L monomers does not decrease by following a simple power law of the concentration but by a function of the form . An origin for such a behaviour is proposed.
Received: 21 November 1997 / Received in final form: 21 April 1998 / Accepted: 24 April 1998 相似文献