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1.
Benhamou M Himmi M Benzouine F Bettachy A Derouiche A 《The European physical journal. E, Soft matter》2004,13(4):353-358
We re-examine here the computation of the effective force between two star-polymers of respective numbers of branches f1 and f2, immersed in a common
-solvent. Such a force originates essentially from the repulsive three-body interactions. To achieve this, we take advantage of some established results using renormalization theory for three-dimensional star-polymers, or conformal invariance for two-dimensional ones. We first show that, in dimension d = 3, the force,
, decreases with the center-to-center distance r as
, with the exact universal amplitude
. Second, in dimension d = 2, we find that the force decays more slowly as
, with the exact universal amplitude
. For high distances compared to the gyration radius,
, of a single polymer chain at the
-point, an exponential decay of the force is expected.Received: 3 February 2004, Published online: 24 May 2004PACS:
61.25.Hq Macromolecular and polymer solutions; polymer melts; swelling - 05.20.-y Classical statistical mechanics 相似文献
2.
We study theoretically the dynamics of living polymers which can add and subtract monomer units at their live chain ends. The classic example is ionic living polymerization. In equilibrium, a delicate balance is maintained in which each initiated chain has a very small negative average growth rate (velocity) just sufficient to negate the effect of growth rate fluctuations. This leads to an exponential molecular weight distribution (MWD) with mean
. After a small perturbation of relative amplitude
, e.g. a small temperature jump, this balance is destroyed: the velocity acquires a boost greatly exceeding its tiny equilibrium value. For
the response has 3 stages: (1) Coherent chain growth or shrinkage, leaving a highly non-linear hole or peak in the MWD at small chain lengths. During this episode, lasting time
, the MWDs first moment and monomer concentration m relax very close to equilibrium. (2) Hole-filling (or peak decay) after
. The absence or surfeit of small chains is erased. (3) Global MWD shape relaxation after
. By this time second and higher MWD moments have relaxed. During episodes (2) and (3) the fast variables (
) are enslaved to the slowly varying number of free initiators (chains of zero length). Thus fast variables are quasi-statically fine-tuned to equilibrium. The outstanding feature of these dynamics is their ultrasensitivity: despite the perturbations linearity, the response is non-linear until the late episode (3). For very small perturbations,
, response remains non-linear but with a less dramatic peak or hole during episode (1). Our predictions are in agreement with viscosity measurements on the most widely studied system,
-methylstyrene.Received: 23 September 2003PACS:
82.35.-x Polymers: properties; reactions; polymerization - 05.40.-a Fluctuation phenomena, random processes, noise, and Brownian Motion - 87.15.Rn Biomolecules: structure and physical properties; Reactions and kinetics; polymerization 相似文献
3.
Swenson J Schwartz GA Bergman R Howells WS 《The European physical journal. E, Soft matter》2003,12(1):179-183
The dynamics of propylene glycol (PG) and its oligomers 7-PG and PPG, with
(about 70 monomers), confined in a Na-vermiculite clay have been investigated by quasi-elastic neutron scattering and dielectric spectroscopy. The liquids are confined to a single molecular layer between the clay platelets, thus giving a true 2D liquid. The results show that the average relaxation time
, deduced from neutron scattering at a momentum transfer Q of about
, is in perfect agreement with the dielectric
-relaxation time, although neutron scattering does not only probe the main (
-) relaxation, but all motions of hydrogens on the experimental time scale. At room temperature
is proportional to Q
2, indicating that the relaxations are mainly due to ordinary translational diffusion. The most unexpected finding is that
(or the dielectric
-relaxation time) is almost unaffected by the 2D confinement, in contrast to the dielectrically active normal mode of PPG which is substantially slower in the confinement. Only the 7-mer has a significantly slower segmental translational diffusion in the clay. The results suggest that the interactions to the clay surfaces are weak and that the present 2D confinement has a very small influence on the time scale of all our observed relaxation processes, except the normal-mode relaxation.Received: 1 January 2003, Published online: 8 October 2003PACS:
61.25.Em Molecular liquids - 68.35.Ja Surface and interface dynamics and vibrations - 61.12.-q Neutron diffraction and scattering 相似文献
4.
C.-M. Ghim E. Oh K.-I. Goh B. Kahng D. Kim 《The European Physical Journal B - Condensed Matter and Complex Systems》2004,38(2):193-199
We investigate a problem of data packet transport between a pair of vertices on scale-free networks without loops or with a small number of loops. By introducing load of a vertex as accumulated sum of a fraction of data packets traveling along the shortest pathways between every pair of vertices, it is found that the load distribution follows a power law with an exponent
. It is found for the Barabási-Albert-type model that the exponent
changes abruptly from
for tree structure to
as the number of loops increases. The load exponent seems to be insensitive to different values of the degree exponent
as long as
.Received: 4 February 2004, Published online: 14 May 2004PACS:
89.75.Fb Structures and organization in complex systems - 05.65. + b Self-organized systems - 02.10.Ox Combinatorics; graph theory 相似文献
5.
We have studied the equilibria of liquid droplets wetting a step edge with an opening angle
by a combination of analytical and numerical methods. Depending on the wetting properties of the substrate walls and on the liquid volume, different locally or globally stable liquid morphologies are found. Complete spreading of the liquid along the bottom edge of the step is observed at equilibrium contact angles
satisfying
. If the contact angle
exceeds a threshold value
the liquid exists in a blob-like configuration. Surprisingly, we find an intermediate regime at a sufficiently high liquid volume and in a range of contact angles
, in which cigar-shaped configurations arise in addition to the blob. We close the paper by a detailed discussion of the stability of this novel liquid morphology.PACS:
47.55.Dz Drops and bubbles - 61.30.Hn Surface phenomena: alignment, anchoring, anchoring transitions, surface-induced layering, surface-induced ordering, wetting, prewetting transitions, and wetting transitions - 68.08.Bc Wetting 相似文献
6.
The quantum dynamics, both non-equilibrium and equilibrium, of the dissipative two-level system is studied by means of the perturbation approach based on a unitary transformation. It works well for the whole parameter range
and
and our main results are: the coherence-incoherence transition is at
; for
the non-equilibrium correlation
; the susceptibility
is of a double peak structure for
and the Shibas relation is exactly satisfied; at the transition point
the equilibrium correlation
in the long time limit.Received: 14 October 2003, Published online: 8 June 2004PACS:
72.20.Dp General theory, scattering mechanisms - 05.30.-d Quantum statistical mechanics 相似文献
7.
Rottereau M Gimel JC Nicolai T Durand D 《The European physical journal. E, Soft matter》2004,15(2):141-148
Diffusion-limited cluster aggregation and gelation are studied using lattice and off-lattice Monte Carlo simulations. The pair correlation function g(r) and the structure factor S(q) of the particle gels were investigated as a function of the volume fraction (
) and time. At volume fractions below
, the gel structure is fractal on small length scales with
. g(r) shows a weak minimum at the correlation length (
), before reaching the average concentration at large length scales. The cut-off function of g(r) varies during the aggregation process, but at a given
, where
is the gel time, it is a universal function of
. At high volume fractions, the structure is dominated by excluded-volume interactions, while at low volume fractions, it is determined by the connectivity.Received: 27 April 2004, Published online: 26 October 2004PACS:
64.60.Ak Renormalization-group, fractal, and percolation studies of phase transitions - 02.70.Uu Applications of Monte Carlo methods 相似文献
8.
M. Benayoun P. David L. DelBuono Ph Leruste H. B. O’Connell 《The European Physical Journal C - Particles and Fields》2003,31(4):525-547
We examine the decay modes
within the context of the hidden local symmetry (HLS) model. Using numerical information derived in previous fits to the
and Ve
+
e
- decay modes in isolation and the
lineshape determined in a previous fit to the pion form factor, we show that all aspects of these decays can be predicted with fair accuracy. Freeing some parameters does not improve the picture. This is interpreted as strong evidence in favor of the box anomaly in the
decays, which occurs at precisely the level expected. We also construct the set of equations defining the amplitudes for
and
at the chiral limit, as predicted from the anomalous HLS Lagrangian appropriately broken. This provides a set of four equations depending on only one parameter, instead of three for the traditional set. This is also shown to match the (two-angle, two-decay-constant)
-
mixing scheme recently proposed and is also fairly well fulfilled by the data. The information returned from the fits also matches expectations from previously published fits to the
decay modes in isolation.Received: 29 June 2003, Revised: 17 September 2003, Published online: 4 November 2003 相似文献
9.
For a self-repelling polymer chain consisting of n segments we calculate the persistence length
, defined as the projection of the end-to-end vector on the direction of the j-th segment. This quantity shows some pronounced variation along the chain. Using the renormalization group and
-expansion we establish the scaling form and calculate the scaling function to order
. Asymptotically, the simple result
emerges for dimension d = 3. Also away from the excluded-volume limit
is found to behave very similar to the swelling factor of a chain of length
. We carry through simulations which are found to be in good accord with our analytical results. For d = 2 both our and previous simulations as well as theoretical arguments suggest the existence of logarithmic anomalies.Received: 17 November 2003, Published online: 30 March 2004PACS:
61.25.Hq Macromolecular and polymer solutions; polymer melts; swelling - 05.10.Cc Renormalization group methods 相似文献
10.
We reconsider the electrostatic contribution to the persistence length,
, of a single, infinitely long-charged polymer in the presence of screening. A Gaussian variational method is employed, taking
as the only variational parameter. For weakly charged and flexible chains, crumpling occurs at small length scales because conformational fluctuations overcome electrostatic repulsion. The electrostatic persistence length depends on the square of the screening length,
, as first argued by Khokhlov and Khachaturian by applying the Odijk-Skolnick-Fixman (OSF) theory to a string of crumpled blobs. We compare our approach to previous theoretical works (including variational formulations) and show that the result
found by several authors comes from the improper use of a cutoff at small length scales. For highly charged and stiff chains, crumpling does not occur; here we recover the OSF result and validate the perturbative calculation for slightly bent rods.PACS:
36.20.-r Macromolecules and polymer molecules - 82.70.-y Disperse systems; complex fluids - 87.15.-v Biomolecules: structure and physical properties 相似文献
11.
We investigate the physics potential of the annihilation decays
in the standard model and beyond. In a naive factorization approach, the branching ratios are estimated to be
and
. In the framework of QCD factorization, we compute the non-factorizable corrections and get
,
. Future measurements of these decays would be useful for testing the factorization frameworks. The smallness of these decays in the SM makes them sensitive probes of new physics. As an example, we will consider the possible admixture of the (V + A) charge current to the standard (V-A) current. This admixture will give a significant contribution to the decays.Received: 29 August 2003, Revised: 17 January 2004, Published online: 19 March 2004Corresponding author: Y.D. Yang 相似文献
12.
We report measurements of birefringence
of several nematic liquid crystals having transverse as well as longitudinal dipole moments in thin (1.4 to
) and thick (7 to
cells. Rubbed polyimide-coated glass plates are used to get planar alignment of the nematic director in these cells. We find significant enhancement (6 to
) of
(
, where S is the orientational order parameter) in thin cells in all compounds with aromatic cores even at temperatures far (
C) below the nematic-isotropic transition point. The enhancement is larger in compounds having several phenyl rings and lower if the number of phenyl rings is reduced. In a compound that does not have an aromatic core no significant enhancement is observed, implying that the strength of the surface potential depends on the aromaticity of the cores. Assuming a perfect orientational order at the surface, calculations based on the Landau-de Gennes theory show that the thickness averaged enhancement of S is sharply reduced as the temperature is lowered in the nematic phase. The measured order parameter S is further enhanced in thin cells because of the stiffening of the elastic constant which reduces the thermal fluctuations of the nematic director. The combined effect is however too small at low temperatures to account for the experimental data.Received: 22 February 2004, Published online: 24 May 2004PACS:
61.30.-v Liquid crystals - 61.30.Pq Microconfined liquid crystals: droplets, cylinders, randomly confined liquid crystals, polymer dispersed liquid crystals, and porous systems - 61.30.Hn Surface phenomena: alignment, anchoring, anchoring transitions, surface-induced layering, surface-induced ordering, wetting, prewetting transitions, and wetting transitionsSurajit Dhara: Present address: Department of Physics, Birla Institute of Technology and Science, Pilani 333 031, India. 相似文献
13.
Buzza DM 《The European physical journal. E, Soft matter》2004,13(1):79-86
Using the complementary approaches of Flory theory and the overlap function, we study the molecular weight distribution and conformation of hyperbranched polymers formed by the melt polycondensation of A-RN0-Bf - 1 monomers in their reaction bath close to the mean field gel point pA = 1, where pA is the fraction of reacted A groups. Here
, N0 is the degree of polymerisation of the linear spacer linking the A group and the f-1 B groups and condensation occurs exclusively between the A and B groups. For
, we assume that the number density of hyperbranched polymers with degree of polymerisation N generally obeys the scaling form
and we explicitly show that this scaling assumption is correct in the mean field regime (here Nl is the largest characteristic degree of polymerisation and the function
cuts off the power law sharply for
). We find the upper critical dimension for this system is dc = 4, so that for
the mean field values for the polydispersity exponent and fractal dimension apply:
, df = 4. For d = 3, mean field theory is still correct for
where
is the Ginzburg point; for
, mean field theory applies on small mass scales N<Nc but breaks down on larger mass scales N>Nc where
is a cross-over mass. Within the Ginzburg zone (i.e., d<dc,
), we show that the hyperbranched chains on mass scales N>Nc are non-Gaussian with fractal dimension given by df = d (for d = 2,3,4). Our results are qualitatively different from those of the percolation model and indicate that the polycondensation of ABf-1, unlike polymer gelation, is not described by percolation theory. Instead many of our results are similar to those for a monodisperse melt of randomly branched polymers, a consequence of the fact that
so that polydispersity is irrelevant for excluded volume screening in hyperbranched polymer melts.Received: 15 December 2003, Published online: 2 March 2004PACS:
82.35.-x Polymers: properties; reactions; polymerization - 05.70.Jk Critical point phenomena 相似文献
14.
Recent observations (Eur. Phys. J. E 9, 135 (2002)) showed that the vitrification process, which sets in during the linear bulk methyl methacrylate (MMA) polymerization carried out below glass transition temperatures, can be modelled by static percolation picture. To generalize this observation for different kind of bulk linear or crosslinked polymers not enough data are present in the literature. To cover partly this deficit we studied the glass transition of MMA and styrene (Sty) crosslinking copolymerization in varying ratios of MMA and Sty. Both the fluorescence intensity I and the lifetime
of pyrene (Py) used as a nanosecond in situ fluoroprobe were monitored during the gelation time. Both I and
increase dramatically as a result of the reduced mobility of the probes trapped in the glassy regions, appearing near the glass transition point. The average size of the glassy regions just below, and the strength of the infinite network formed upon the connection of the glassy regions above the glass transition point
obey power law relations. The data around
were interpreted on the basis of the percolation theory and we observed that the corresponding exponents
and
give static percolation values independent of the polymer composition.Received: 9 July 2004, Published online: 1 October 2004PACS:
64.60.Ak Renormalization-group, fractal, and percolation studies of phase transitions - 64.70.Pf Glass transitions - 82.35.Jk Copolymers, phase transitions, structure 相似文献
15.
A method is proposed to calculate the confidence level for agreement of data with the Higgs sector of the Standard Model (SM). This is done by combining information from direct and indirect Higgs Boson searches. Good agreement with the SM is found for
GeV using the observables most sensitive to mH: Al and mW. In particular, quantum corrections, as predicted by the SM, are observed with a statistical significance of forty-four standard deviations. However, apparent deviations from the SM of 3.7
and 2.8
are found for the Z
and right-handed Zb
couplings respectively. The maximum confidence level for agreement with the SM of the entire data set considered is
for
GeV. The reason why confidence levels about an order of magnitude higher than this have been claimed for global fits to similar data sets is explained.Received: 8 September 2004, Revised: 22 March 2005, Published online: 18 May 2005 相似文献
16.
The spin-parity analysis of the data on the
annihilation reaction at rest in liquid and in gaseous hydrogen at 3 bar pressure and in flight at
momentum of
MeV/c, collected by the Obelix spectrometer at the LEAR complex of CERN, is presented. The relative branching ratios
and
are obtained. It is also shown that the inclusion of the exotic meson
, JPC = 1- + , mass and width
,
GeV/c2, in its decay to
, improves the fit and some implications of these results are briefly discussed. The relative S and P-wave annihilation percentages in four charged pions at two target densities are obtained.Received: 2 December 2003, Published online: 23 April 2004 相似文献
17.
Resonant active-to-active (
), as well as active-to-sterile (
) neutrino (
) oscillations can take place during the core bounce of a supernova collapse. Besides, over this phase, weak magnetism increases the antineutrino (
) mean free path, and thus its luminosity. Because the oscillation feeds mass-energy into the target
species, the large mass-squared difference between the species (
) implies a huge amount of energy to be given off as gravitational waves (
erg s-1), due to anisotropic but coherent
flow over the oscillation length. This asymmetric
-flux is driven by both the spin-magnetic and the universal spin-rotation coupling. The novel contribution of this paper stems from (1) the new computation of the anisotropy parameter
-0.01, and (2) the use of the tight constraints from neutrino experiments as SNO and KamLAND, and the cosmic probe WMAP, to compute the gravitational-wave emission during neutrino oscillations in supernovae core collapse and bounce. We show that the mass of the sterile neutrino
that can be resonantly produced during the flavor conversions makes it a good candidate for dark matter as suggested by Fuller et al. , Phys. Rev. D 68, 103002 (2003). The new spacetime strain thus estimated is still several orders of magnitude larger than those from
diffusion (convection and cooling) or quadrupole moments of neutron star matter. This new feature turns these bursts into the more promising supernova gravitational-wave signals that may be detected by observatories as LIGO, VIRGO, etc., for distances far out to the VIRGO cluster of galaxies.Received: 26 November 2003, Revised: 26 February 2004, Published online: 3 June 2004 相似文献
18.
We compute the one-loop
-functions describing the renormalisation of the coupling constant
and the frequency parameter
for the real four-dimensional duality-covariant non-commutative
-model, which is renormalisable to all orders. The contribution from the one-loop four-point function is reduced by the one-loop wavefunction renormalisation, but the
-function remains non-negative. Both
and
vanish at the one-loop level for the duality-invariant model characterised by
. Moreover,
also vanishes in the limit
, which defines the standard non-commutative
-quantum field theory. Thus, the limit
exists at least at the one-loop level.Received: 19 March 2004, Published online: 5 May 2004 相似文献
19.
Measurements of the time-dependent CP-asymmetry in the decay
and its charge conjugate by the BELLE and BABAR collaborations currently yield
and
, characterizing the direct and mixing-induced CP-asymmetries, respectively. We study the implication of these measurements on the CKM phenomenology taking into account the available information in the quark mixing sector. Our analysis leads to the results that the ratio |P
c
/T
c
| involving the QCD-penguin and tree amplitudes and the related strong phase difference
in the
decays are quite substantial. Using the isospin symmetry to constrain |P
c
/T
c
| and
, where
parameterizes the penguin-induced contribution, we present a fit of the current data including the measurements of
and
. Our best-fits yield
,
,
,
, and
. At 68% C.L., the ranges are
,
,
,
and
. Currently en vogue dynamical approaches to estimate the hadronic matrix elements in
decays do not provide a good fit of the current data.Received: 5 April 2004, Published online: 14 July 2004A.Ya. Parkhomenko: On leave of absence from Department of Theoretical Physics, Yaroslavl State University, Sovietskaya 14, 150000 Yaroslavl, Russia. 相似文献
20.
In the SUSY SO(10) GUT context, we study the exclusive processes
. Using the Wilson coefficients of the relevant operators including the new operators
which are induced by neutral Higgs boson (NHB) penguins, we evaluate some possible observables associated with these processes like the invariant mass spectrum (IMS), lepton pair forward-backward asymmetry (FBA), lepton polarization asymmetries etc. In this model the contributions from Wilson coefficients
, among new contributions, are dominant. Our results show that the NHB effects are sensitive to the FBA,
, and
of
decay, which are expected to be measured in B factories, the deviation of
in
can reach 0.1 from SM, which could be seen in B factories, and the average of the normal polarization
can reach several percent for
and it is 0.05 or so for
, which could be measured in the future super B factories and provide useful information to probe new physics and discriminate different models.Received: 30 October 2004, Published online: 9 March 2005 相似文献