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1.
Refractive index and density measurements have been carried out on three nO.m liquid crystalline compounds, namely, 4O.2, 4O.3 and 1O.10 belonging to the N-(p-n-alkoxybenzylidene)-p-n-alkylaniline series. From the data, the orientational order parameter has been estimated using Vuks and Neugebauer local field models. Furthermore, the orientational order parameter has been calculated directly from refractive index data employing the Vuks scaling factor method, Neugebauer f(B) parameter, effective geometry parameter and a method proposed by Kuczyński et al. It is observed that order parameter values estimated from different methods agree well near the nematic–isotropic transition and diverge as the nematic phase attains equilibrium. The temperature gradient of refractive indices and the nematic crossover temperatures have also been estimated for these compounds. The results obtained are compared and discussed. 相似文献
2.
3.
Refractive index and density measurements of two cyano nematogens, namely p-hexyloxybenzylidene p-aminobenzonitrile and p-octyloxybenzylidene p-aminobenzonitrile have been carried out. From these data, orientational order parameter S has been estimated using different methods. Principal polarizabilities have been calculated using the well-known Vuks isotropic and Neugebauer anisotropic models. Polarizability anisotropy has been estimated using Lippincott δ-function, molecular vibration, Haller's extrapolation and Vuks scaling methods. Using these values, the orientational order parameter S has been estimated at different temperatures in their nematic phases. The values obtained have been compared and discussed. Further, using the experimental refractive index data, the nematic crossover temperatures have also been estimated for these compounds. 相似文献
4.
Some years ago we developed an automatized reflectometric method to measure the surface azimuthal anchoring energy of nematic
liquid crystals on an optically isotropic substrate. This method provides a high accuracy and sensitivity but requires the
use of wedge glass plates and a sufficiently high anisotropy of the intensity reflectivity coefficients. This latter condition
restricts greatly the number of possible substrates that can be investigated with this technique. Here we develop a new reflectometric
method which offers comparable or better accuracy and sensitivity but does not require wedge plates and high anisotropy of
the reflectivity coefficients. The method is fully automated and provides a direct measurement of the azimuthal director angle.
The experimental procedure exploits the dependence of the reflectivity tensor on the surface director orientation. The measurement
of the azimuthal angle does not require any knowledge of the optical parameters of the nematic material and of the optically
isotropic substrate, and provides an absolute accuracy better than 0.2° in the whole range 0-360° and a sensitivity better than 0.1°. This reflectometric method can be also used with weakly anisotropic substrates as well as thin rubbed polymeric layers.
In this latter case, the effective uncertainty in the measurement of the director azimuthal angle depends on the substrate
anisotropy. A simple and direct experimental procedure to estimate this uncertainty is proposed.
Received 8 January 2002 and Received in final form 27 February 2003 / Published online: 15 April 2003
RID="a"
ID="a"e-mail: faetti@df.unipi.it 相似文献
5.
EPR study of Dy
3 +
ions in DyBa
2
Cu
3
O
6 + x 总被引:1,自引:0,他引:1
V. Likodimos N. Guskos J. Typek M. Wabia 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(2):143-147
Concentrated polycrystalline DyBa2Cu3O6+x compounds are studied by X-band EPR spectroscopy. A broad resonance line due to the highly anisotropic EPR spectrum of Dy3+ ions is identified on several specimens at low temperatures. Powder simulation of the EPR spectra complies with the ground
Kramers doublet predicted by crystal field analysis of Dy3+ ions. Calculations of the second and fourth moments of the resonance lines due to the dipole-dipole interactions of Dy3+ indicate the presence of substantial exchange narrowing of the dipolar-broadened EPR linewidth.
Received 3 June 2001 相似文献
6.
Y. W. Yao F. G. Wu Z. L. Hou Y. Y. Liu 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(4):353-360
The transmission and reflection coefficients of two-dimensional semi-infinite solid-solid phononic crystal systems and fluid-fluid
phononic waveguide structures have been investigated. The numerical results show that the transmission spectra for longitudinally
and transversally polarized incident waves are different, and the spectra of the transmission and reflection coefficients
of the semi-infinite system agree well with the band structure. The numerical results show that when a guided wave incident,
localized modes are excited, and different polarities have different coupling efficiencies with the incident guided wave.
At the same time, far from the cutoff frequency, the guided wave couples out of semi-infinite waveguide highly efficiently. 相似文献
7.
Th. Brückel D. Hupfeld J. Strempfer W. Caliebe K. Mattenberger A. Stunault N. Bernhoeft G.J. McIntyre 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(4):475-490
We report on X-ray resonance exchange and neutron scattering of metallic GdS. At the LII and L III absorption edges of Gd, resonance enhancements of more than two orders of magnitude over the non-resonant magnetic scattering
are observed. Polarisation analysis proves that these enhancements are due to dipolar transitions from the 2p to the 5d states. The branching ratio between the LII and L III edges of 2.5 suggests a polarisation of the 5d electrons in the ground state. The antiferromagnetic order is of type II in the fcc lattice. Single crystal diffraction of
hot neutrons suggests that the spin direction lies within the (111) planes with a value for the sublattice magnetisation of
6.51(3) . The critical exponent for the sublattice magnetisation has a value of β = 0.38(2) in agreement with a pure Heisenberg model.
Above T
N, a sharp component persists in the critical diffuse scattering. Lattice distortions give indications for two additional low-temperature
phase transitions at about 49 K and 32 K. We argue that these transitions are not connected to spin reorientations and discuss
the possible influence of fourth-order exchange interactions.
Received 19 November 1999 and Received in final form 12 December 2000 相似文献
8.
L. Zhang W. Kleemann J. Dec R. Wang M. Itoh 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(2):163-171
The dielectric permittivity ε′ - i
of SrTi 18O 3 (STO18) is studied under a dc electric field E as a function of the temperature, T. In ε′
vs.
T, a double-peak is found when 0 < E < 30 KV/m. While the peak at high-T is attributed to the smeared ferroelectric phase transition, the low-T one is induced by domain wall motion. The transverse Ising model including an external homogeneous and quenched random-fields
is successfully used to describe both the smeared phase transition and the domain wall response in the low-T domain state. The calculations are in good agreement with the experimental results.
Received 4 January 2002 / Received in final form 25 March 2002 Published online 19 July 2002 相似文献
9.
D. Hupfeld W. Schweika J. Strempfer W.A. Caliebe U. Köbler K. Mattenberger G.J. McIntyre F. Yakhou Th. Brückel 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):273-289
We report on an investigation of the magnetic properties of Gd
x
Eu
1 - x
S mixed crystals with compositions in the range of 0.6 <
x
< 1. For the two samples Gd
0.8
Eu
0.2
S and Gd
0.73
Eu
0.27
S a long-range antiferromagnetic order was observed at low temperatures. Element-specific measurements exhibited a different
temperature dependence of the reduced sublattice magnetisation of the two magnetic species. A model calculation and Monte
Carlo simulations revealed that the different temperature dependence is due to frustration effects. These frustration effects
lead to a breakdown of the long-range order for higher europium contents. For the Gd
0.67
Eu
0.33
S-sample we were able to observe a short-range antiferromagnetic order with correlation lengths of a few 10? with X-ray resonance exchange scattering.
Received 25 April 2001 and Received in final form 3 December 2001 相似文献
10.
T. Renk 《The European Physical Journal A - Hadrons and Nuclei》2001,11(3):251-255
Following a prior analysis of measured pp elastic differential cross-sections, the impact parameter representation in terms of profile functions is calculated from
two different parametrizations of single diffractive dissociation data. The derivative of this quantity, with respect to the
collision energy squared s, measures the growth rate of the reaction's blackness. Its distribution in impact parameter space allows detailed insight
into the growth pattern of the total diffractive cross-section and the approaching unitarity limit. Comparing the results
with the elastic case, the different mechanisms of unitarization of two parametrizations are discussed.
Received: 19 January 2001 / Accepted: 11 July 2001 相似文献
11.
J. Souletie Y. Tabata T. Taniguchi Y. Miyako 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(1):43-46
The usual scaling equations at a phase transition, employed out of their usual validity range, with Tc a negative constant, fit properties observed in correlated electron systems with unmatched accuracy. We illustrate this behavior
with our data in Ce(Ru1-xRhx)2Si2 for x
= 0.4 and 0.5 and comment these results and what they imply physically.
Received 22 June 1998 and Received in final form 29 September 1998 相似文献
12.
V.A. Pashchenko A. Sulpice F. Mila P. Millet A. Stepanov P. Wyder 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(4):473-476
We report on the magnetic susceptibility and electron spin resonance measurements on polycrystalline samples of the vanadium
oxide VOSb2O4, a quasi-one-dimensional S
= 1/2 Heisenberg system. The susceptibility vanishes at zero temperature, but there is no cusp at the onset of the susceptibility
drop, and the ESR linewidth exhibits an increase characteristic of a phase transition at a much lower temperature. We show
that this behaviour is consistent with the formation of a pseudo-gap in a spin-Peierls system in the adiabatic limit.
Received 7 February 2001 and Received in final form 24 April 2001 相似文献
13.
A.A. Tarasenko F. Nieto L. Jastrabík C. Uebing 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,12(2):311-322
A two-dimensional lattice-gas model with square symmetry is investigated by using the real-space renormalization group (RSRG)
approach with blocks of different size and symmetries. It has been shown that the precision of the method depends strongly
not only on the number of sites in the block but also on its symmetry. In general, the accuracy of the method increases with
the number of sites in the block. The minimal relative error in determining the critical values of the interaction parameters
is equal to . Using the RSRG method, we have explored phase diagrams of both a two-dimensional Ising spin model and of a square lattice
gas with lateral interactions between adparticles. We also have investigated the influence of the attractive and repulsive
interactions on both the thermodynamic properties of the lattice gas and the diffusion of adsorbed particles over surface.
We have calculated adsorption isotherms and coverage dependences of the pair correlation function, isothermal susceptibility
and the chemical diffusion coefficient. In addition, we have included in our analysis the interaction of the activated particle
in the saddle point with its nearest neighbors. We have also used Monte Carlo (MC) technique to calculate these dependences.
Despite the fact that both methods constitute very different approaches, the correspondence of the numerical data is surprisingly
good. Therefore, we conclude that the RSRG approach can be applied to characterize the thermodynamic and kinetic properties
of systems of particles with strong lateral interactions.
Received 1st September 1998 and Received in final form 8 March 2000 相似文献
14.
G. Rakotovelo P. S. Moussounda M. F. Haroun P. Légaré A. Rakotomahevitra J. C. Parlebas 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,57(3):291-297
Progress of scanning tunneling microscopy (STM) allowed to handle various molecules adsorbed on a given surface. New concepts
emerged with molecules on surfaces considered as nano machines by themselves. In this context, a thorough knowledge of surfaces
and adsorbed molecules at an atomic scale is thus particularly invaluable. In this work, within the framework of density functional
theory (DFT), we present an electronic and structural ab initio study of a BaTiO3 (001) surface (perovskite structure) in its paraelectric phase. As far as we know the atomic and molecular adsorption of
oxygen at surface is then analyzed for the first time in the literature. Relaxation is taken into account for several layers.
Its analysis for a depth of at least four layers enables us to conclude that a reasonable approximation for a BaTiO3 (001) surface is provided with a slab made up of nine plans. The relative stability of two possible terminations is considered.
By using a kinetic energy cut off of 400 eV, we found that a surface with BaO termination is more stable than with TiO2 termination. Consequently, a surface with BaO termination was chosen to adsorb either O atom or O2 molecule and the corresponding calculations were performed with a coverage 1 on a (1×1) cell. A series of cases with O2 molecule adsorbed in various geometrical configurations are also analyzed. For O2, the most favorable adsorption is obtained when the molecule is placed horizontally, with its axis, directed along the Ba-Ba
axis and with its centre of gravity located above a Ba atom. The corresponding value of the adsorption energy is -9.70 eV
per molecule (-4.85 eV per O atom). The molecule is then rather extended since the O–O distance measures 1.829 ?. By comparison,
the adsorption energy of an O atom directly located above a Ba atom is only -3.50 eV. Therefore we are allowed to conclude
that the O–O interaction stabilizes atomic adsorption. Also the local densities of states (LDOS) corresponding to various
situations are discussed in the present paper. Up to now, we are not aware of experimental data to be compared to our calculated
results. 相似文献
15.
D. Vignolles V. N. Laukhin A. Audouard M. Nardone T. G. Prokhorova E. B. Yagubskii E. Canadell 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(1):53-60
The Shubnikov-de Haas (SdH) oscillation spectra of the
-(BEDT-TTF)4(NH4)[ Cr(C2O4)3] .DMF
organic metal have been studied in pulsed magnetic fields of up to
either 36 T at ambient pressure or 50 T under hydrostatic
pressures of up to 1 GPa. The ambient pressure SdH oscillation
spectra can be accounted for by up to six fundamental frequencies
which points to a rather complex Fermi surface (FS). A noticeable
pressure-induced modification of the FS topology is evidenced
since the number of frequencies observed in the spectra
progressively decreases as the pressure increases. Above 0.8 GPa,
only three compensated orbits are observed, as it is the case for
several other isostructural salts of the same family at ambient
pressure. Contrary to other organic metals, of which the FS can be
regarded as a network of orbits, no frequency combinations are
observed for the studied salt, likely due to high magnetic
breakdown gap values or (and) high disorder level evidenced by
Dingle temperatures as large as ≃7 K. 相似文献
16.
Y. Yuan K. Deng Y. Liu C. Tang G. Lu J. Yang X. Wang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,40(2):243-246
The ground state structures of MC3 (M = Sc, V, and Cr) and their
anions have been investigated, employing the first-principles DFT
at the B3LYP level. The calculations predict that the equilibrium
geometries of both neutral MC3 and their anions are cyclic
structures with C2v symmetry. The Mulliken charge and spin
populations of MC3 and their anions have also been calculated,
and it is found the electron charge changes mainly take place on
the M atoms from anions to neutral molecules. The low-lying
excited states for the clusters are calculated with time-dependent
DFT to assign the features of the photoelectron spectra. Our
results agree well with the available experimental and theoretical
data. 相似文献
17.
M. Castelnovo P. Sens J.-F. Joanny 《The European physical journal. E, Soft matter》2000,1(2-3):115-125
We investigate the equilibrium charge distribution along a single annealed polyelectrolyte chain under different conditions.
The coupling between the conformation of the chain and the local charge distribution is described for various solvent qualities
and salt concentration. In salt free solution, we find a slight charge depletion in the central part of the chain: the charges
accumulate at the ends. The effect is less important if salt is added to the solution since the charge inhomogeneity is localized
close to the chain ends over a distance of order of the Debye length. In the case of poor solvent conditions we find a different
charge per monomer in the beads and in the strings in the framework of the necklace model. This inhomogeneity leads to a charge
instability and a first order transition between spherical globules and elongated chains.
Received 19 March 1999 and Received in final form 2 August 1999 相似文献
18.
E. Biémont P. Palmeri P. Quinet E. Träbert C.J. Zeippen 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(1):37-44
Transitions between the five fine-structure levels in the 3s
23p
3 ground configuration of Fe XII (P-like) are of interest in astrophysics and terrestrial plasma diagnostics. The decay rates
give rise to level lifetimes in the millisecond range, which have been measured recently at a heavy-ion storage ring. While
most of the 3s
23p
23d levels are short-lived, two of these levels have no E1 decay channels and may also have millisecond lifetimes. We present
HFR and MCDF calculations of the E1, M1, E2 and M2 transition rates between the 3s
23p
3, 3s3p4 and 3s
23p
23d levels and compare the lifetime results to most recent experimental data as well as to other predictions.
Received 2 October 2001 / Received in final form 22 January 2002 Published online 28 June 2002 相似文献
19.
20.
Joanna Hetmaczyk ukasz Hetmaczyk Anna Migda‐Mikuli Edward Mikuli Aleksandra Weseucha‐Birczyska 《Journal of Raman spectroscopy : JRS》2012,43(8):1118-1125
[Ba(H2O)3](ClO4)2 between 90 and 300 K possesses two solid phases. One phase transition of the first‐order type at: = 211.3 K (on heating) and = 204.6 K (on cooling) was determined by differential scanning calorimetry. The entropy change value (ΔS ≈ 15 Jmol–1 K–1), associated with the observed phase transition, indicates a moderate degree of molecular dynamical disorder. Both, vibrational and reorientational motions of H2O ligands and ClO4– anions, in the high‐temperature and low‐temperature phases, were investigated by Fourier transform far‐infrared and middle‐infrared and Raman light scattering spectroscopies. The temperature dependences of the full‐width at half‐maximum values of the bands associated with ρw(H2O) mode, in both infrared (~570 cm–1) and Raman light scattering (~535 cm–1) spectra, suggest that the observed phase transition is not associated with a sudden change of a speed of the H2O reorientational motions. Ligands reorient fast, with correlation time of the order of several picoseconds, with a mean activation energy value Ea = 5.1 kJ mol–1 in both high and low temperature phases. On the other hand, measurements of temperature dependences of full‐width at half‐maximum values of the infrared band at ~460 cm–1, associated with δd(OClO)E mode, and Raman band at ~1105 cm–1, associated with νas(ClO)F2 mode, revealed the existence of a fast ClO4– reorientation in phase I and in phase II, with the Ea(I) and Ea(II) values equal to 8.0 and 6.5 kJ mol–1, respectively. These reorientational motions of ClO4– are slightly distorted at the TC. Fourier transform far‐infrared and middle‐infrared spectra with decreasing of temperature indicated characteristic changes at the vicinity of PT at TC, which suggested lowering of the crystal structure symmetry. All these experimental facts suggest that the discovered phase transition is associated with small change of H2O ligands and somewhat major change of ClO4– anions reorientational dynamics, and with insignificant change of the crystal structure, too. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献