共查询到20条相似文献,搜索用时 15 毫秒
1.
A. Steyerl B.G. Yerozolimsky A.P. Serebrov P. Geltenbort N. Achiwa Yu.N. Pokotilovski O. Kwon M.S. Lasakov I.A. Krasnoshchokova A.V. Vasilyev 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(3):299-304
Ultracold neutrons (UCN) are lost from traps if they are quasi-elastically scattered from the wall with an energy gain sufficient
to exceed the Fermi potential for the wall. Possible mechanisms of a quasi-elastic energy transfer are, for instance, scattering
from hydrogen diffusing in an impurity surface layer or on surface waves at a liquid wall. Using two different experimental
methods at the UCN source of the Institut Laue-Langevin we have investigated both the energy-gain and the energy-loss side
of quasi-elastic UCN scattering on Fomblin grease coated walls. For Fomblin oil and similar new types of oil we report up-scattering
data as a function of temperature and energy transfer. These low-temperature oils may be used in an improved measurement of
the neutron lifetime, which requires extremely low wall reflection losses.
Received 13 March 2002 Published online 31 July 2002 相似文献
2.
Chord length distributions describe size, shape and spatial arrangement of geometrical objects (particles). The chord length
distribution is in principle proportional to the second derivative of the correlation function of small-angle scattering.
It is calculable from a relative measurement of the scattering intensity I(h). In structure research, the characterization of numerous particle systems can be achieved by comparing experimental chord
distributions with theoretical ones, provided the latter are available with sufficiently high precision for a lot of fundamental,
universal shapes. Both sides of this concept are exemplified: – the step from a relative measurement of the scattering intensity
of an isotropic two-phase sample to the chord length distribution (errors in and in , limited h-interval, corresponding to the region (1-2) nm < r in real space, must be observed); as well as the geometric matter of calculation of chord distributions as fingerprints for
basic geometric figures, including the non-convex case.
Received 15 March 1999 and Received in final form 26 April 2000 相似文献
3.
R. Lefort B. Toudic J. Etrillard F. Guillaume P. Bourges R. Currat T. Breczewski 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(1):51-57
The diffraction pattern of n-alkane/urea inclusion compounds is known to contain a broad diffuse scattering related to the
molecular form factor of the alkane species, indicating individual rotational and/or translational disorder of these molecules.
Inelastic coherent neutron scattering reveals for the first time the entirely dynamical character of the alkane molecular
disorder around room temperature. This observation fully agrees with a recent model of the coherent scattering cross section
of totally uncorrelated motions. In the ordered phase this diffuse scattering remains, but elastic, and very low energy molecular
vibrational modes are evidenced. These observations are discussed in relation with previous incoherent neutron scattering
results.
Received 9 February 2001 and Received in final form 1st August 2001 相似文献
4.
A. Michels J. Weissmüller 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(1):57-65
This paper presents a calculation of the magnetic small-angle neutron scattering cross-section resulting from a dilute ensemble
of superparamagnetic particles exhibiting uniaxial magnetic anisotropy. We focus on the two experimentally relevant scattering
geometries in which the incident neutron beam is perpendicular or parallel to an applied magnetic field, and we discuss several
orientations of the anisotropy axes with respect to the field. Magnetic anisotropy has no influence on the magnetic small-angle
neutron scattering when the particles are mobile, as is the case e.g. in ferrofluids, but, when the particles are embedded
in a rigid non-magnetic matrix and the orientations of the anisotropy axes are fixed, significant deviations compared to the
case of negligible anisotropy are expected. For the particluar situation in which the anisotropy axes are parallel to the
applied field, closed-form expressions suggest that an effective anisotropy energy or anisotropy-energy distribution can be
determined from experimental scattering data.
Received 8 November 2001 相似文献
5.
A. Schalchli-Plaszczynski L. Auvray 《The European physical journal. E, Soft matter》2002,7(4):339-344
We study by small-angle neutron scattering the vesicle-to-micelle transition induced by anchoring diblock copolymers on the
surfactant membranes. Vesicles are made using the ternary system SDS (sodium dodecyl sulfate)/octanol/PS-POE (polystyrene-polyoxyethylene),
chosen as a model of more complex biological systems. The anchored polymer chains destabilize the membranes and lead to the
formation of mixed polymer-surfactant micelles. We show that there is no influence of the polymer mass on the membranes destabilization.
We compare this experimental result with recent theoretical predictions concerning the polymer-grafted membranes. We have
a good agreement with predictions involving membrane curvature effects, and also with predictions focusing on more local deformations
of membranes created by the grafted chains.
Received 12 June 2001 and Received in final form 18 March 2002 相似文献
6.
Structure and properties of some glass-forming liquid alloys 总被引:1,自引:0,他引:1
U. Dahlborg M. Calvo-Dahlborg P.S. Popel V.E. Sidorov 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(4):639-648
Some physical properties (kinematic viscosity, surface tension and magnetic susceptibility) of some Fe-based metallic melts
of easily glass-forming alloys have been measured during heating and subsequent cooling. The results indicate that molten
liquid metallic alloys undergo a number of structural transformations ranging from the initial microheterogeneous state formed
after melting up to the true solution state. Studies by small angle neutron scattering on a eutectic SnPb melt confirm this
conclusion in that two families of different sizes have been seen, one in the range 1 to 2 nm and one of size larger than
100 nm. Both kind of particles have relatively sharp interfaces and the size of the smaller particles is found to depend on
temperature.
Received 25 February 1999 and Received in final form 28 October 1999 相似文献
7.
E.S. Clementyev K. Conder A. Furrer I.L. Sashin 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(4):465-467
We provide here experimental data on the phonon density-of-states of MgB2 obtained by the inelastic neutron scattering technique. The measurements were performed for the natural boron-based magnesium
diboride with use of a time-of-flight neutron spectrometer. Several phonon bands were observed in the phonon spectrum at energies
of about 33, 55, 82 and 99 meV. We show that the cut-off energy of the density-of-states occurs at around 105 meV which is
much higher than expected so far from heat-capacity data and partially explains the high T
c
value observed for MgB2. The characteristic phonon energies are indicative of an intermediate coupling regime in this compound. We conclude that
a much needed neutron experiment aimed at the study of the isotopic effect in the phonon density-of-states of MgB2 is conceivable.
Received 19 March 2001 相似文献
8.
Rivière C Wilhelm C Cousin F Dupuis V Gazeau F Perzynski R 《The European physical journal. E, Soft matter》2007,22(1):1-10
The internal structure of biological vesicles filled with magnetic
nanoparticles is investigated using the following complementary analyses:
electronic transmission microscopy, dynamic probing by magneto-optical
birefringence and structural probing by Small Angle Neutron Scattering
(SANS). These magnetic vesicles are magnetic endosomes obtained via a
non-specific interaction between cells and anionic magnetic iron oxide
nanoparticles. Thanks to a magnetic purification process, they are probed at
two different stages of their formation within HeLa cells: (i) adsorption of
nanoparticles onto the cellular membrane and (ii) their subsequent
internalisation within endosomes. Differences in the microenvironment of the
magnetic nanoparticles at those two different stages are highlighted here.
The dynamics of magnetic nanoparticles adsorbed onto cellular membranes and
confined within endosomes is respectively 3 and 5 orders of magnitude slower
than for isolated magnetic nanoparticles in aqueous media. Interestingly,
SANS experiments show that magnetic endosomes have an internal structure
close to decorated vesicles, with magnetic nanoparticles locally decorating
the endosome membrane, inside their inner-sphere. These results, important
for future biomedical applications, suggest that multiple fusions of
decorated vesicles are the biological processes underlying the endocytosis
of that kind of nanometric materials. 相似文献
9.
L. Saviot E. Duval J.F. Jal A.J. Dianoux 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(4):661-666
Relaxations in amorphous bis-phenol A polycarbonate are studied by neutron scattering, as a function of temperature below
the glass transition. Two different processes are observed. One is very fast, with a characteristic time (∼ 0.3 ps), that
is independent of temperature and momentum transfer. Conversely the other is slower, with a time which is dependent on temperature
and momentum transfer. The very fast localized anharmonic motion is interpreted by the overdamping of low-frequency vibrational
modes, by nearby dynamic holes. The slower relaxation is thermally activated and momentum transfer dependent. It corresponds
to molecular group motions and possibly to the short-time regime of the segmental relaxation.
Received 29 February 2000 and Received in final form 13 June 2000 相似文献
10.
W. Essafi F. Lafuma C.E. Williams 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(2):261-266
We show experimentally that Manning counterion condensation also leads to a renormalization of the charge density at high
concentrations of highly charged, flexible, hydrophilic polyelectrolytes. Investigations by small angle neutron and X-ray
scattering of semi-dilute solutions of poly(acrylamide-co-sodium-2-acrylamido-2-methylpropane sulfonate) at different charge densities above the condensation threshold, show that
the scattering function is invariant with the charge density.
Received 16 June 1998 相似文献
11.
Aqueous solutions of a well-defined poly(N-isopropylacrylamide-co-sodium 2-acrylamido-methylpropanesulfonate) (NIPAM/NaAMPS in a 95/5 molar ratio) have been investigated by means of small-angle
neutron scattering (SANS) and rheological experiments as a function of temperature ( 25°
C
T
60°
C) and polymer concentration ( 0.5wt%
C
12wt%). The solutions remain optically transparent and isotropic over the whole temperature range, in contrast with the homopolyNIPAM
which precipitates above its lower critical solution temperature (LCST = 32°
C). Upon addition of salt, the systems undergo a micro-macrophase separation. At temperatures above 45°
C, the SANS spectra exhibit a sharp peak at a scattering wave vector, q
max, which increases slightly with temperature. At high temperature ( T∼ 60°
C), the scattered intensity follows a power law I(q) ∼q
-4 in the asymptotic regime, characteristic of two-density media with sharp interfaces, and q
max is found to vary with polymer concentration as q
max∼C
0.22. Estimates of the typical sizes give values between 40 ? and 200 ?. These results provide a strong evidence of a thermally
induced microphase separation, which is corroborated by the very sharp increases of the viscosity (over 2 decades) and of
the stress relaxation time of the solutions, occurring in the temperature range where the scattering peak is observed. The
results are discussed and compared with the theoretical models proposed for weakly charged polyelectrolytes in a poor solvent.
Received 1 October 2001 相似文献
12.
Neutron scattering from equilibrium-swollen networks 总被引:1,自引:0,他引:1
Sukumaran SK Beaucage G Mark JE Viers B 《The European physical journal. E, Soft matter》2005,18(1):29-36
Small-angle neutron scattering measurements were performed on end-linked poly (dimethylsiloxane) (PDMS) networks swollen to
equilibrium with d-benzene. Comparison was made with equivalent concentration PDMS solutions. Equilibrium-swollen networks
consistently displayed a linear scattering regime at low q followed by a good-solvent-like scaling regime at high q in agreement with the predictions of the Gel Tensile Blob (GTB) model. Data are fit using the unified function modified for
the GTB model (3-parameter fit). Equilibrium-swollen networks display a base structural size, the gel tensile-blob size, ξ,
that was found to be independent of the molecular weight between crosslinks for the series of molecular weights studied, consistent
with the predictions of the model. The length of the extended tensile structure, L, can be larger than the length of the fully extended network strand. The predicted scaling relationship for L, L ∼ Q1/2Navg, where Navg = (1/fNc2+1/4Ne2
, Q is the equilibrium swelling ratio, Nc is the molecular weight between crosslinks, Ne is the entanglement molecular weight and f is the crosslink functionality is in agreement with experimental results for the networks studied. 相似文献
13.
We present small angle neutron scattering measurements on binary aqueous solutions of some short-chain amphiphiles (diols,
triols, glycols and diglycols) at room temperature. The spectra were analysed in terms of the Teubner-Strey phenomenological
formula which allows to obtain a measure for the amphiphilicity strength of each system (amphiphilicity factor f
a). In some systems, however, other models, valid for micellar solutions, give also a good representation of the spectra. As
a result, we find that, independently of the type of hydrophilic group side (oxydrilic or oxirane), these systems cover the
entire accessible amphiphilicity scale ( -1 < f
a < 1). Some disordered systems ( f
a > 1) presumably are able to form micelle-like aggregates.
Received 12 June 2002 Published online: 16 April 2003
RID="a"
ID="a"e-mail: giovanni.darrigo@uniroma1.it 相似文献
14.
Gotter M Sottmann T Baciu M Olsson U Wennerström H Strey R 《The European physical journal. E, Soft matter》2007,24(3):277-295
Time-resolved small-angle neutron scattering (TR-SANS) was employed to observe temperature-induced phase transitions from
the sponge (L
3 to the lamellar ( L
α phase, and vice versa, in the water-oil (n -decane)-non-ionic surfactant ( C12E5 system using both bulk and film contrast. Samples of different bilayer volume fractions φ and solvent viscosities η were
investigated applying various amplitudes of temperature jump ΔT . The findings of a previous 2H -NMR study could be confirmed, where the lamellar phase formation was determined to occur through a nucleation and growth
process, while it was concluded that the L
3 -phase develops in a mechanistically different and more rapid manner involving uncorrelated passage formation. Likewise,
the kinetic trends of the nucleation and growth transition (decreased transition time with increase of φ and ΔT were witnessed once again. Additionally, NMR and SANS data that demonstrate a strong dependency of that process on solvent
viscosity η are presented. Contrariwise, it is made evident via both SANS and NMR results that the L
α -to-L
3 transition time is independent (within experimental sensitivity) of the varied parameters (φ , ΔT , η . Unusual scattering evolution in one experiment, originating from a highly ordered lamellar phase, intriguingly hints
that a major rate determining factor is the disruption of long-range order. Furthermore, the bulk contrast investigations
give insight into structure peak shifts/development during the transitions, while the film contrast experiments prove the
bilayer thickness to be constant throughout the phase transitions and show that there is no evidence for a change in the short-range
order of the bilayer structure. The latter was considered possible, due to the different topology of the L
3 and L
α phases. Lastly, an unexpected yet consistent appearance of anisotropic scattering is detected in the L
3 -to- L
α transitions. 相似文献
15.
Chen SH Mallamace F Faraone A Gambadauro P Lombardo D Chen WR 《The European physical journal. E, Soft matter》2002,9(3):283-286
We detect in a tri-block co-polymer micellar system an ergodic-to-nonergodic-to-ergodic transition, as a function of temperature,
in a range of concentrations, by photon correlation measurements. The shear viscosity is also shown to jump two order of magnitude
at these transition temperatures. Surprisingly, the structure factor as measured by small angle neutron scattering shows a
marked narrowing at the structural arrest state. Rationalization of these results with the existence of an attractive branch
in the phase diagram of an attractive colloid system predicted by mode coupling theory is made.
Received 9 Aprile 2002 相似文献
16.
17.
Holderer O Frielinghaus H Monkenbusch M Allgaier J Richter D Farago B 《The European physical journal. E, Soft matter》2007,22(2):157-161
The dynamical properties of bicontinuous microemulsions have been studied with neutron spin echo spectroscopy around length
scales corresponding to the correlation peak q0. Comparison of samples with different contrasts for neutrons shed light on the two modes dominated either by variation of
the oil/water difference or surfactant concentration in the hydrodynamic regime. The results have been compared to theoretical
predictions of the relaxation rates of bicontinuous microemulsions by Nonomura and Ohta [M. Nonomura, T. Ohta, J. Chem. Phys.
110, 7516 (1999)]. The influence of modification of the surfactant layer bending constants in the microemulsion by addition of
homopolymers (polyethylenepropylene: PEPX and polyethyleneoxide: PEOX, X=5 kg/mol), dissolved in the oil phase and water, has been investigated. 相似文献
18.
T. Striffler U. Stuhr H. Wipf H. Hahn S. Egelhaaf 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(2):245-251
By means of small-angle neutron scattering the microstructure of two nanocrystalline Pd samples (prepared by inert gas condensation)
has been studied at room temperature in a Q-range from [0pt] to [0pt] . An additional subsequent doping of the two samples with H as well as with D (concentrations < 4 at%) caused contrast variations
that provided more detailed structural information. The measured scattering intensity was modeled by a Porod contribution
from large heterogenities (e.g. pores) and a contribution from spherical grains with a log-normal distribution of their radii. To account for the presence
of grain boundaries, the grains were considered to be surrounded by a shell with a reduced Pd density and a thickness half
as large as the thickness of the grain boundaries. For the above model, the data of the H-doped, D-doped and undoped sample
were simultaneously fitted with one single set of adjustable parameters. The fits yielded for the two samples volume-weighted
mean grain radii of 10 nm and 13 nm. The values for the grain boundary thickness lie between 0.2 and 0.8 nm. Almost all of
the H- and D-atoms are, at low hydrogen concentrations, located in the grain boundaries.
Received 1 May 2000 相似文献
19.
Inoue R Kanaya T Nishida K Tsukushi I Taylor J Levett S Gabrys BJ 《The European physical journal. E, Soft matter》2007,24(1):55-60
We studied the dynamic anisotropy and heterogeniety of polystyrene thin films in glassy state with inelastic neutorn scattering. Adjusting the scattering vector to the directions parallel and perpendicular to the film surface, we observed the elastic scattering intensities as a function of temperature. It was found for the 200 A film that the elastic intesity decreased with increasing temperature more rapidly in the perpendicular direction than in the pararell direction, showing the higher mobility in the perpendicular direction. However, such dynamical anisotropy was not observed in the 1000 A film. The decrease in the mobility was observed with the film thickness in both the directions. These results were explained in terms of an interface hard layer. We also evelauated the dynamical heterogeniety from the non-Gaussian parameter A0, which increased with decreasing the film thickness, showing the increase in the dynamical heterogeneity. Assuming a simple bi-layer model consisting of the interface hard layer and the bulk-like layer, we analyzed the thickness dependence of the non-Gaussian parameter A0 and the mean square displacement (u2) to find that the hard layer has a thickness of approximately 130 A and a mean square displacement of approximately 0.018 A2 at 230 K. 相似文献
20.
A. Michels J. Weissmüller R. Birringer 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(4):533-540
Based on a micromagnetics model, we develop a method through which quantitative information on the volume-averaged mean-square
magnetostatic stray field 〈|H
b
d|2〉
v due to non-zero divergences of the magnetization M within the bulk of a ferromagnetic body can be obtained by analysis of magnetic-field-dependent small-angle neutron scattering
data. In the limit of high applied magnetic field H
a, when the direction of M deviates only sligthly from H
a, we have estimated a lower bound for 〈|H
b
d|2〉
v as a function of the external field, and we have applied the method to bulk samples of nanocrystalline electrodeposited Ni
and Co and coarse-grained polycrystalline cold-worked Ni. The root-mean-square magnetostatic stray field, which is inherent
to a particular magnetic microstructure, shows a pronounced field dependence, with values ranging from about 5 to 50mT. Even
at applied fields as large as 1.7T, the quantity μ〈|H
b
d|2〉1/2
v of nanocrystalline Co is still 24mT, which suggests that contributions to the total magnetostatic field originating from
the bulk are significant in nanocrystalline ferromagnets; therefore, 〈|H
b
d|2〉
v cannot be ignored in the interpretation of e.g. measurements of magnetization or spin-wave resonance. A comparison of 〈|H
b
d|2〉
v with the volume-averaged mean-square anisotropy field reveals that both quantities are of comparable magnitude.
Received 25 April 2002 Published online 31 October 2002
RID="a"
ID="a"e-mail: anmi@nano.uni.saarland.de 相似文献