共查询到20条相似文献,搜索用时 562 毫秒
1.
Grimau M Laredo E Sánchez F López-Carrasquero F Báez ME Bello A 《The European physical journal. E, Soft matter》2004,15(4):383-393
A series of poly(
-n-alkyl
-L-aspartates) which are nanophase self-assembled comb-like polymers has been studied by dielectric spectroscopy in a broad frequency range ( 10-23×106 Hz), with n-alkyls side chains of various lengths, 10n18. In every member of the series the same relaxations were identified after the decomposition of the experimental isothermal trace in up to three peaks with relaxation times distributions. The strength, width and average relaxation time for all the relaxation modes were determined for each material. Besides the local low temperature, Arrhenius modes, two relaxation modes,
and
, present a cooperative character whose dynamics are not affected by the side chains melting. The
relaxation is a polyethylene-like glass transition of the amorphous side chains and its dynamics is strongly dependent on the n value due to the increasing restrictions imposed by the self-assembled confinement. The strength of the
relaxation mode increases as the lateral chains loose their 2D order. The restricted chopstick motion of the rigid rods is thought to be the origin of the
mode; this motion is hindered at temperatures where the cage size decreases as a result of the increasing disorder with temperature. 相似文献
2.
We present here a theoretical study of the early kinetics of the microphase separation in crosslinked polymer blends, made of two incompatible polymers A and B, dissolved in a common good solvent. Use is made of an extended blob model used previously for the investigation of the static properties of such a transition. We are interested in the variation of the relaxation rate,
, versus the wave number q, in the vicinity of the spinodal temperature. We first show that kinetics is entirely dominated by local motions, which are of Rouse type. Slow motions are absent, because of the permanent presence of crosslinks. Second, we find that the characteristic frequency,
(q ) =
, increases with increasing wave number q according to a sixth power law, that is
(q )
q6{-9/4}, where is the overall monomer volume fraction. Therefore, the swelling of strands due to the excluded-volume forces leads to a renormalization of the characteristic frequency by a multiplicative factor scaling as {-9/4}. The main conclusion is that the presence of a good solvent necessitates relaxation rates less important than those relative to crosslinked mixtures in the molten state. 相似文献
3.
M. Diehl A. Manashov A. Schäfer 《The European Physical Journal A - Hadrons and Nuclei》2006,29(3):315-326
We analyze the moments of the isosinglet generalized parton distributions H, E,
,
of the nucleon in one-loop order of heavy-baryon chiral perturbation theory. We discuss in detail the construction of the
operators in the effective theory that are required to obtain all corrections to a given order in the chiral power counting.
The results will serve to improve the extrapolation of lattice results to the chiral limit. 相似文献
4.
We study soft hadron production in relativistic heavy-ion collisions in a wide range of reaction energy, 4.8 GeV <
< 200 GeV, and make predictions about yields of particles using the statistical hadronization model. In fits to experimental
data, we obtain both the statistical parameters as well as physical properties of the hadron source. We identify the properties
of the fireball at the critical energy threshold, 6.26 GeV <
< 7.61 GeV, marking for higher energies the hadronization of an entropy-rich phase. In terms of the chemical composition,
one sees a phase which at low energy is chemically under-saturated, and which turns into a chemically over-saturated state
persisting up to the maximum accessible energy. Assuming that there is no change in physical mechanisms in the energy range
15 >
≥200 GeV, we use continuity of particle yields and statistical parameters to predict the hadron production at
= 62.4 GeV, and obtain total yields of hadrons at
= 130 GeV. We consider, in depth, the pattern we uncover within the hadronization condition, and discuss possible mechanisms
associated with the identified rapid change in system properties at
. We propose that the chemically over-saturated 2 + 1 flavor hadron matter system undergoes a 1st-order phase transition. 相似文献
5.
Approximately 438 pb-1 of e + e- data from the OPAL detector, taken with the LEP collider running at centre-of-mass energies of 192-209 GeV, are analyzed to search for evidence of chargino pair production,
, or neutralino associated production,
. Limits are set at the 95% confidence level on the product of the cross-section for the process
and its branching ratios to topologies containing jets and missing energy, or jets with a lepton and missing energy, and on the product of the cross-section for
and its branching ratio to jets. R-parity conservation is assumed throughout this paper. When these results are interpreted in the context of the Constrained Minimal Supersymmetric Standard Model, limits are also set on the masses of the
and
, and regions of the parameter space of the model are ruled out. Nearly model-independent limits are also set at the 95% confidence level on
with the assumption that each chargino decays via a W boson, and on
with the
assumed to decay via a Z0.Received: 15 December 2003, Revised: 16 February 2004, Published online: 23 April 2004 相似文献
6.
First measurements of
mesons production properties and their spin alignment in
charged current (CC) and neutral current (NC) interactions are presented. The analysis of the full data sample of the NOMAD
experiment is performed in different kinematic regions. For
and
mesons produced in
CC interactions and decaying into
we have found the following yields per event:
and
respectively, while for the
and
mesons produced in
interactions the corresponding yields per event are:
and
. The results obtained for the
parameter,
and
for
and
produced in
CC interactions, are compared to theoretical predictions tuned on LEP measurements in
annihilation at the
pole. For
mesons produced in
interactions the measured
parameter is
.
PACS 13.15.+g, 13.60.Le, 13.87.Fh, 13.88.+e, 14.40.Ev 相似文献
7.
8.
A. Shebeko P. Papakonstantinou E. Mavrommatis 《The European Physical Journal A - Hadrons and Nuclei》2006,27(2):143-155
The one-body and two-body density matrices in coordinate space and their Fourier transforms in momentum space are studied
for a nucleus (a nonrelativistic, self-bound finite system). Unlike the usual procedure, suitable for infinite or externally
bound systems, they are determined as expectation values of appropriate intrinsic operators, dependent on the relative coordinates
and momenta (Jacobi variables) and acting on intrinsic wave functions of nuclear states. Thus, translational invariance (TI)
is respected. When handling such intrinsic quantities, we use an algebraic technique based upon the Cartesian representation,
in which the coordinate and momentum operators are linear combinations of the creation and annihilation operators
and
for oscillator quanta. Each of the relevant multiplicative operators can then be reduced to the form: one exponential of
the set {
} times another exponential of the set {
}. In the course of such a normal-ordering procedure we offer a fresh look at the appearance of “Tassie-Barker” factors, and
point out other model-independent results. The intrinsic wave function of the nucleus in its ground state is constructed from
a nontranslationally-invariant (nTI) one via existing projection techniques. As an illustration, the one-body and two-body
momentum distributions (MDs) for the 4He nucleus are calculated with the Slater determinant of the harmonic-oscillator model as the trial, nTI wave function. We
find that the TI introduces quite important effects in the MDs. 相似文献
9.
Lu CY Chen P Ishii Y Komura S Kato T 《The European physical journal. E, Soft matter》2008,25(1):91-101
We measure the non-linear relation between the shear stress and shear rate in the lyotropic lamellar phase of C12E5 /water system. The measured shear thinning exponent changes with the surfactant concentration. A simple rheology theory of
a lamellar or smectic phase is proposed with a prediction
∼ σ3/2 , where
is the shear rate and σ is the shear stress. We consider that the shear flow passed through the defect structure causes the
main dissipation. As the defect line density varies with the shear rate, the shear thinning arises. The defect density is
estimated by the dynamic balance between the production and annihilation processes. The defect production is caused by the
shear-induced layer undulation instability. The annihilation occurs through the shear-induced defect collision process. Further
flow visualization experiment shows that the defect texture correlates strongly with the shear thinning exponent. 相似文献
10.
D. Elsner A. Süle P. Barneo P. Bartsch D. Baumann J. Bermuth R. Böhm D. Bosnar M. Ding M. Distler D. Drechsel I. Ewald J. Friedrich J. M. Friedrich S. Grözinger P. Jennewein S. Kamalov F. H. Klein M. Kohl K. W. Krygier H. Merkel P. Merle U. Müller R. Neuhausen Th. Pospischil M. Potokar G. Rosner H. Schmieden M. Seimetz O. Strähle L. Tiator Th. Walcher M. Weis 《The European Physical Journal A - Hadrons and Nuclei》2006,27(1):91-97
The reaction p(e, e'p)π0 has been studied at Q2 = 0.2 (GeV/c)2 in the region of W = 1232MeV. From measurements left and right of
, cross-section asymmetries ρLT have been obtained in forward kinematics ρLT(
= 20°) = (- 11.68±2.36stat±2.36sys) and backward kinematics ρLT(
= 160°) = (12.18±0.27stat±0.82sys) π0. Multipole ratios
{S1+ * M1+}/| M1+|2 and
{S0+ * M1+}/| M1+|2 were determined in the framework of the MAID2003 model. The results are in agreement with older data. The unusally strong
negative
{S0+ * M1+}/| M1+|2 required to bring also the result of Kalleicher et al. in accordance with the rest of the data is almost excluded. 相似文献
11.
H. Ðapo B. -J. Schaefer J. Wambach 《The European Physical Journal A - Hadrons and Nuclei》2008,36(1):101-110
Single-particle potentials in Hartree-Fock approximation for different hyperon-nucleon (YN channels are calculated in the framework of the effective low-momentum YN interaction
. In contrast to the nucleon-nucleon interaction, the available experimental data for the YN interaction are scarce. As a consequence, no unique YN low-momentum potential
can be predicted from the various bare potentials. The resulting momentum- and density-dependent single-particle potentials
for several different bare OBE models and for chiral effective field theory are compared to each other. 相似文献
12.
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
13.
Searches for stable, hadronizing scalar quarks and gluinos are performed using the data collected with the ALEPH detector at LEP. Gluon splitting into a gluino or a squark pair is searched for at centre-of-mass energies around the Z resonance, in the e + e-
and
processes. Stable squark pair production, and stop pair production with subsequent decays into a stable gluino,
, are also directly searched for at centre-of-mass energies from 183 to 209 GeV. Altogether, stable hadronizing stop (sbottom) quarks are excluded up to masses of 95 (92)
, and stable hadronizing gluinos are excluded up to 26.9
, at 95% confidence level. In the framework of R-parity-conserving supersymmetric models in which the gluino and the stop quark are the two lightest supersymmetric particles, a 95% C.L. lower limit of 80
is set on the stop quark mass.Received: 23 May 2003, Published online: 24 October 2003 相似文献
14.
R.A. Diaz R. Martinez C.E. Sandoval 《The European Physical Journal C - Particles and Fields》2006,46(2):403-405
We find some constraints on the flavor changing vertices of the two Higgs doublet model, from the
measurement. Although bounds from this observable have already been considered, this paper takes into account the role of
a new operator not included previously, as well as the vertices
,
and
. Using the Cheng–Sher parametrization, we find that for a relatively light charged Higgs boson (200–300 GeV), we obtain
, while the parameter
could have values up to about 50. In addition, we use bounds for
and
obtained from
at next to leading order, and study the case where the only vanishing vertex factors are the ones involving quarks from the
first family. We obtain that
is not sensitive to the change of the parameter
, while
. 相似文献
15.
R. K. Sinha A. Dhal P. Agarwal S. Kumar Monika B. B. Singh R. Kumar P. Bringel A. Neusser R. Kumar K. S. Golda R. P. Singh S. Muralithar N. Madhavan J. J. Das K. S. Thind A. K. Sinha I. M. Govil R. K. Bhowmik J. B. Gupta P. K. Joshi A. K. Jain S. C. Pancholi L. Chaturvedi 《The European Physical Journal A - Hadrons and Nuclei》2006,28(3):277-281
High-spin states in 79Rb were populated in the reaction
at E(beam) = 60 MeV. The lifetimes of the excited states of the
positive-parity yrast band and of the
negative-parity band in 79Rb were measured by the Doppler Shift Attenuation Method. The deduced transition quadrupole moments Qt are found to have a decreasing trend with rotational frequency for both the bands, consistent with those found experimentally
in neighbouring nuclei.
An erratum to this article is available at . 相似文献
16.
Conducting polymers as driving electrodes for Polymer-Dispersed Liquid-Crystals display devices: On the electro-optical efficiency 总被引:1,自引:0,他引:1
Roussel F Chan-Yu-King R Buisine JM 《The European physical journal. E, Soft matter》2003,11(3):293-300
Intrinsically conducting polymer (ICP) thin films are used as driving electrodes for Polymer-Dispersed Liquid-Crystals (PDLC) display devices. In order to investigate the electro-optical efficiency of these organic electrodes, three different kinds of conducting polymers, i.e. polyaniline doped with 10-camphorsulfonic acid (PANI(HCSA)), polypyrrole doped with dodecylbenzenesulfonic acid (PPY(DBSA)), and polyethylenedioxythiophene doped with polystyrenesulfonate (PEDOT(PSS)), were prepared or purchased, and coated either on glass or plastic substrates. Optical absorption studies in the UV-Vis range of the conducting polymer-coated substrates were first performed showing the presence of conducting species for the three types of polymers. The electrical characteristics of the resulting films were measured with the four-probes technique. PANI(HCSA) exhibits a higher conductivity
(
) compared to PPY(DBSA)
(
), and PEDOT(PSS)
(
). It is also shown that for a given conducting polymer, its electrical conductivity decreases when a plastic substrate is used. These observations have been related to significant morphological changes observed by scanning electron microscopy (SEM). A mixture of Norland Optical Adhesive 65 and nematic liquid-crystal E7 in the weight ratio (35:65) was used as precursor of the PDLC material. Better electro-optical responses (transmission properties, drive voltages and switching times) of PDLC films were obtained for devices prepared with (PPY(DBSA))-based electrodes. The electro-optical performances of the PDLC display devices also depend on the nature of the ICP substrate used.Received: 25 September 2002, Published online: 29 July 2003PACS:
73.61.Ph Polymers; organic compounds - 42.79.Kr Display devices, liquid-crystal devices - 82.35.Cd Conducting polymers - 42.70.Df Liquid crystals F. Roussel: rfred@purple.univ-littoral.fr 相似文献
17.
After deriving the projected stress tensor in cylindrical geometry for a fluid membrane described by the Helfrich Hamiltonian,
we calculate the average force f exerted by a thermally fluctuating nanotubule of radius R , and its standard deviation
f . We obtain f and
f in terms of the internal membrane tension , the bending rigidity , the temperature k
B
T and a molecular cutoff . We find for f a shift ∼ 1/ with respect to the mean field behavior ∼ . We obtain (
f )2 ∼ R ln(R/b) where b is a molecular length,
f being typically small compared to f . Taking into account the difference between the internal tension and the actual mechanical tension applied to the membrane from which the tubule is drawn, we discuss the amplitude of the fluctuation-induced corrections to
the average force. Our results, obtained in the harmonic approximation, hold for tubules with aspect ratio not larger than
200 , of radius significantly smaller than 100nm, that are connected to a large membrane reservoir, e.g., a giant vesicle. 相似文献
18.
A presence of a Meissner-Ochsenfeld effect in a gas of spin 1/2 fermions with an interaction
, where
is a volume of a region
in real space which is taken by thesystem and
with
,
satisfying Fermi anticommutation relations, is investigated. The effect proves to be weaker than in BCS by a factor 3/4 at T = 0, implying a greater penetration depth
of external magnetic field. V
4 is nonzero only within a thin layer of 1-fermion energies around the chemical potential .Received: 14 June 2004, Published online: 12 October 2004PACS:
74.20.-z Theories and models of superconducting state - 74.20.Fg BCS theory and its development 相似文献
19.
The reaction
is discussed within a covariant effective meson-nucleon theory. The model is adjusted to data of the subreaction
. Our focus is on di-electrons from Dalitz decays of η -mesons,
, and the role of the corresponding transition form factor
. Numerical results are presented for the intermediate-energy kinematics of HADES experiments. 相似文献
20.
We present a superfield Lax formalism of the superspace sigma model based on the target space
and show that a one-parameter family of flat superfield connections exists if the target space
is a symmetric space. The formalism has been related to the existence of an infinite family of local and non-local superfield
conserved quantities. A few examples have been given to illustrate the results. 相似文献