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1.
The dependence of the electric field gradients (EFG) in Hafnium-Hydride systems as a function of the composition H/Hf in the
cubic δ and tetragonal ε phases were investigated using the time-dependent perturbed angular correlation (TDPAC) technique,
with181Ta as the nuclear probe. Two EFGs were found in the ε phase, indicating the existence of two major symmetries surrounding
the Ta probe. The results indicate that the trend of the EFGs, in the ε phase, are due to the changes in the lattice parametersa
o,c
o as hydrogen is added to the Hf-H system. In the δ phase, only one major symmetry was found. Both phases are characterized
by broad frequency distributions and large anisotropies. 相似文献
2.
A mean-field theory for domain structures in random multiblock copolymer melts is developed. We focus on the finite molecular
weight effects resulting in a competition between macroscopic phase separation and microdomain formation in the system. We
identify an essential parameter N
ε controlling the phase behavior of the system, where N is the number of blocks per chain and ε is the composition asymmetry parameter (= the difference between the mean copolymer
composition and its critical value). The phase diagram involving N
ε and the reduced temperature as variables is obtained. The regions of coexistence of two or more phases are identified. We
show that a superstructure formation on cooling is always pre-empted by a macroscopic phase separation of the macroscopically
homogeneous (disordered) system yielding two homogeneous phases: H
0↦H
1 + H
2. The third (lamellar) phase separates on further cooling. Then hexagonal and body-centred-cubic phases take over if N
ε
1. As the Flory interaction parameter χ increases further, the standard transitions BCC↦HEX↦LAM take place.
Received 13 July 2001 相似文献
3.
Observation of relaxation modes in room temperature ferroelectric liquid crystal mixtures 总被引:1,自引:0,他引:1
The dielectric measurements in SmC* and SmA phases of a room temperature ferroelectric liquid crystal mixture FLC-6980 in
the cells of different thickness in planer alignment have been carried out in the frequency range 100 Hz to 1 MHz. A relaxation
mode (called NRM) whose dielectric increment is less than the Goldstone mode has been observed in the SmC* phase. This mode
appears due to the surface effect. Goldstone mode and the soft mode was observable in the vicinity of SmC*-SmA transition
temperature (T
C*A). The dielectric parameters of the Goldstone mode, new mode and the soft mode have been studied as a function of frequency
and temperature. The calculated values for fNRM, δεNRM and distribution parameter αNRM are found to be 325 kHz, 6 and 0.156 for 5μm thick planer cell at 37°C. It is seen that in the vicinity of theT
C*A, soft mode obeys the Curie-Weiss law given by mean field theory. The results have been compared with materials of large spontaneous
polarization. 相似文献
4.
Infrared asymptotic behavior of a scalar field, passively advected by a random shear flow, is studied by means of the field
theoretic renormalization group and the operator product expansion. The advecting velocity is Gaussian, white in time, with
correlation function of the form μ d(t-t¢) / k^d-1+x\propto\delta(t-t') / k_{\bot}^{d-1+\xi}, where k
⊥=|k
⊥| and k
⊥ is the component of the wave vector, perpendicular to the distinguished direction (‘direction of the flow’)—the d-dimensional generalization of the ensemble introduced by Avellaneda and Majda (Commun. Math. Phys. 131:381, 1990). The structure functions of the scalar field in the infrared range exhibit scaling behavior with exactly known critical
dimensions. It is strongly anisotropic in the sense that the dimensions related to the directions parallel and perpendicular
to the flow are essentially different. In contrast to the isotropic Kraichnan’s rapid-change model, the structure functions
show no anomalous (multi)scaling and have finite limits when the integral turbulence scale tends to infinity. On the contrary,
the dependence of the internal scale (or diffusivity coefficient) persists in the infrared range. Generalization to the velocity
field with a finite correlation time is also obtained. Depending on the relation between the exponents in the energy spectrum
E μ k^1-e\mathcal{E} \propto k_{\bot}^{1-\varepsilon} and in the dispersion law w μ k^2-h\omega\propto k_{\bot}^{2-\eta}, the infrared behavior of the model is given by the limits of vanishing or infinite correlation time, with the crossover
at the ray η=0, ε>0 in the ε–η plane. The physical (Kolmogorov) point ε=8/3, η=4/3 lies inside the domain of stability of the rapid-change regime; there is no crossover line going through this point. 相似文献
5.
A.A. Boulbitch P. Tolédano 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(3):355-362
The behaviour of the antiferroelectric SmCA liquid crystal phase under applied electric field is discussed theoretically. The phase diagram involving the SmA, SmCA and SmC
A
* phases is worked out and shown to exhibit a Lifshitz critical point. The deformation of the bilayer structures induced by
the field transforms the SmCA phases into a ferrielectric phase whose specific configuration is described.
Received: 23 October 1997 / Revised: 8 April 1998 / Accepted: 14 July 1998 相似文献
6.
We found an exact expression for the Flory radius R
F of Gaussian polymers placed in an external periodic field. This solution is expressed in terms of the two parameters η and
a that describe the reduced strength of an external field and the period of the field to the polymer gyration radius ratio,
respectively. R
F is found to be a decaying function of η for any values of a . Provided that the gyration radius is of the order of the period of an external field or less, the ground-state (GS) approximation
of the exact result for R
F is shown to give qualitatively incorrect results. In addition to the “ground-state” contribution, the exact solution for
R
F contains an additional term that is overlooked by the GS approximation. This term gives rise to the fact that R
F as a function of η exhibits power law behavior (rather than exponential decay obtained from the GS result) once η exceeds
the threshold value ηcon . 相似文献
7.
Simultaneous calculation of the dipole moment μj and the relaxation time τj of a certain number of non-spherical rigid aliphatic polar liquid molecules (j) in non-polar solvents (i) under 9.8 GHz electric
field is possible from real ε′ij and imaginary ε″ij parts of the complex relative permittivity ε*ij. The low frequency and infinite frequency permittivities ε0ij and ε∞ij measured by Purohitet al [1,2] and Srivastava and Srivastava [3] at 25, 35 and 30°C respectively are used to obtain static μs. The ratio of the individual slopes of imaginary σ″ij and real σ′ij parts of high frequency (hf) complex conductivity σ*ij with weight fractionsw
jatw
j → 0 and the slopes of σ″ij— σ′ij curves for differentw
js [4] are employed to obtain τjs. The former method is better in comparison to the existing one as it eliminates polar-polar interaction. The hf μjs in Coulomb metre (C m) when compared with static and reported μs indicate that μs s favour the monomer formations which combine to form dimers in the hf electric field. The comparison among μs shows that
a part of the molecule is rotating under X-band electric field [5]. The theoretical μtheos from available bond angles and bond moments of the substituent polar groups attached to the parent molecules differ from
the measured μjs and μs to establish the possible existence of mesomeric, inductive and electromeric effects in polar liquid molecules. 相似文献
8.
S. To Y. H. Zhu W. B. Lee X. M. Liu Y. B. Jiang G. Y. Tang 《Applied Physics A: Materials Science & Processing》2009,96(4):939-944
Phase transformations of an electropulsing-treated ZA22 alloy were studied after tensile deformation by using scanning electron
microscopy and transmission electron microscopy. It was found that electropulsing tremendously accelerated phase transformations
consequentially in the two stages: (a) quenching from supersaturated state approaching the final stable state, i.e., α+ε→T′+η, and (b) up-quenching from the final stable state to a higher temperature state, i.e., T′+η→α+ε. The mechanism of electropulsing-induced phase transformation is discussed from the point of view of Gibbs free energy, and
electropulsing kinetics. 相似文献
9.
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
10.
István Lagzi 《Pramana》2005,64(2):291-298
Formation of 1D Liesegang patterns was studied numerically in precipitation and reversible complex formation of precipitate
scenarios in an electric field. The Ostwald’s supersaturation model reported by Buki, Kárpáti-Smidróczki and Zrínyi (BKZ model)
was extended further. In the presence of an electric field the position of the first and the last bands (X
n) measured from the junction point of the outer and the inner electrolytes can be described by the functionX
n =a
1τ
n
1/2
+a
2τn +a
3, where τn is the time elapsed until the nth band formation,a
1,a
2 anda
3 are constants. The variation of the total number of bands with different electric field strengths (ε) has a maximum. For
higher ε one can observe a moving precipitation zone that becomes wider due to precipitation and reversible complex formation. 相似文献
11.
In this paper, we research the dynamical evolution and quasinormal modes of nonminimal derivative coupling scalar field in
Reissner-Nordstr?m spacetime with a global monopole. We also find that Hawking radiation behavior near the event horizon is
similar to the scalar field case. In the whole spacetime, the conclusions show that weak coupling field will affect the dynamical
behavior delicately, but the strong coupling constant η results in the deformation of dynamical evolution curve. When η > η
c
, the black hole system will not be stable. The break from the global monopole also intensely affect the dynamical behavior
of this black hole spacetime. Furthermore, the break will promote the instability of the coupling field. 相似文献
12.
A. I. Burkhanov K. P. Guzhakovskaya L. I. Ivleva 《Bulletin of the Russian Academy of Sciences: Physics》2011,75(10):1399-1402
The dielectric nonlinearity in an SBN-75 single crystal doped with 0.01 at % Cr was investigated in the vicinity of a diffuse
phase transition by studying the reverse dielectric dependences ε′(E
=). The influence of illumination and exposure (aging) on the behavior of ε′(E
=) was demonstrated. A reduction in the dielectric memory effect after sample illumination was detected. 相似文献
13.
Ali Akbar Ashkarran Azam Iraji?zad Seyed Mohammad Mahdavi Mohammad Mahdi Ahadian Mohammad Reza Hormozi?Nezhad 《Applied Physics A: Materials Science & Processing》2009,96(2):423-428
The microstructural (XRD and SEM) and dielectric behavior of Pb(Zr0.54Ti0.46)O3 (PZT 54/46) ceramic system with donor (La, Nb and La+Nb) doping was studied. For all Nb-doped PZT samples, only one (tetragonal) phase was found, which confirms the compositional
shifts near the morphotropic phase boundary. For La- and La+Nb-doped samples, there are two (rhombohedral and tetragonal)
phases. Dielectric characteristic behavior (1/ε) for La- and La+Nb-doped PZT was associated with two-phase transitions: Ferro–Ferro at low temperature and Ferro–Para at Curie temperature.
For Nb-doped samples, only one phase transition is observed, which indicates the presence of a single ferroelectric phase. 相似文献
14.
W. Huang R. Richert 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,66(2):217-221
We investigate the nonlinear dielectric effects in a polar viscous liquid, propylene carbonate, by analyzing the voltage and
current traces obtained for a sinusoidal electric field at a frequency of 1 kHz and field amplitudes as high as 162 kV/cm.
The main source of non-linear behavior results from the energy absorbed from the field and is understood quantitatively. However,
there is a qualitative difference in the behavior of the field induced change, Δε′′(E), and the third harmonic amplitude of the current, I3ω. Although both Δε′′(E) and I3ω are considered reliable measures of non-linear behavior, we show here that the third harmonic signal reflects only those
non-linear responses that are instantaneous on the time scale of the test frequency. 相似文献
15.
The laser light scattering technique for non-invasivein situ simultaneous measurements on elastic constants and viscosity coefficients of nematic liquid crystals is introduced. By measuring
the autocorrelation function of the scattered light from nematic liquid crystals at different scattering angles, the splay
and twist elastic constantsK
11 andK
22 are obtained from the amplitudes of the autocorrelation function, and the viscosity coefficients ofη
Splay andη
Twist are determined using the viscoelastic ratiosK
11/η
Splay andK
22
η
Twist from the telaxation parameters of the two modes. 相似文献
16.
The solidified microstructure of bulk undercooled Ag40Cu30Ge30 alloy consists of three parts: primary (Ge) phase, the complex structure of (Ag + Ge) and (Ag + ε
2) pseudobinary eutectics, and (Ag + Ge + ε
2) ternary eutectic. In comparison, the pseudobinary eutectic no longer appears in an alloy droplet solidified in a drop tube.
Once the undercooling exceeds 225 K and the cooling rate is greater than 2×103 K s−1, the microstructure of the solidified droplet is totally composed of anomalous ternary eutectic. In both cases, the primary
(Ge) phase exhibits various faceted growth morphologies at different undercoolings, such as columnar block, long dendrite,
equiaxed dendrite and rod-like crystal. Some refined side branches grow from the equiaxed (Ge) dendritic branches composed
of {111} twins, which is ascribed to the rapid epitaxial growth of (Ag + Ge) pseudobinary eutectic from the (Ge) dendritic
branches. Moreover, both the primary (Ge) phase and the (Ge) phase in the (Ag + Ge) pseudobinary eutectic are effective heterogeneous
nuclei for the (Ag+ε
2) pseudobinary eutectic. As undercooling increases, the (Ge) phase in the (Ag + Ge+ε
2) ternary eutectic transforms from faceted to non-faceted phase, while the independent nucleation and growth of the (Ag) and
ε
2 phases in the ternary eutectic displaces their previous cooperative growth. These growth kinetics transitions result in the
formation of anomalous ternary eutectic. 相似文献
17.
Ruiting Sun Xiaoli Wang Jing Shi Le Wang 《Applied Physics A: Materials Science & Processing》2011,104(1):129-133
New perovskite solid solution ceramics of (1−x)BaTiO3-xBi(Mg1/2Ti1/2)O3 ((1−x)BT-xBMT, x≤0.09) were synthesized by the solid-state reaction technique. X-ray diffraction studies have revealed a stable single perovskite
structure for all samples. Dielectric measurements were carried out at different frequencies and temperatures. The polarization
evolutions with temperatures were measured to investigate the ferroelectric properties. All the compositions show features
of ferroelectrics with diffuse phase transition, though the temperature T
m
of their dielectric constant maximum ε
m
is frequency dependent. The dielectric constant peak ε(T) of (1−x)BT-xBMT ceramics become broad with increasing BMT content. During the temperature range of ε(T) peak summit, (1−x)BT-xBMT ceramics present quasi-linear dielectric phenomenon under high electric field with very high dielectric constant. 相似文献
18.
The static conductivity σ(E) and photoconductivity (PC) at radiation frequencies ħω=10 and 15 meV in Si doped with shallow impurities (density N=1016−6×1016 cm−3, ionization energy ε1≃45 meV) with compensation K=10−4−10−5 in electric fields E=10–250 V/cm are measured at liquid-helium temperatures T. Special measures are taken to prevent the high-frequency part of the background radiation (ħω>16 meV) from striking the
sample. It is found that the conductivity σ(E) is due to carrier motion along the D
− band, which is filled with carriers under the influence of the field E. In fields E<E
q
(E
q
≃100–200 V/cm) the carrier motion consists of hops along localized D
− states in a 10–15 meV energy band below the bottom of the free band (energy ε=ε1); for E>E
q
carriers drift along localized D
− states with energy ε∞ε1−10 meV. An explanation is proposed for the threshold behavior of the field dependence of the photo-and static conductivities.
Pis’ma Zh. éksp. Teor. Fiz. 66, No. 4, 232–236 (25 August 1997) 相似文献
19.
The liquid to solid transformation of ternary Ag42.4Cu21.6Sb36 eutectic alloy was accomplished in an ultrasonic field with a frequency of 35 kHz, and the growth mechanism of this ternary eutectic was examined. Theoretical calculations predict that the sound intensity in the liquid phase at the solidification interface increases gradually as the interface moves up from the sample bottom to its top. The growth mode of (ε θ Sb) ternary eutectic exhibits a transition of "divorced eutectic- mixture of anomalous and regular structures-regular eutectic" along the sample axis due to the inhomogeneity of sound field distribution. In the top zone with the highest sound intensity, the cavitation effect promotes the three eutectic phases to nucleate independently, while the acoustic streaming efficiently suppresses the coupled growth of eutectic phases. In the meantime, the ultrasonic field accelerates the solute transportation at the solid-liquid interface, which reduces the solute solubility of eutectic phases. 相似文献
20.
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