共查询到20条相似文献,搜索用时 31 毫秒
1.
A.J. Jin M.R. Fisch M.P. Mahajan K.A. Crandall P. Chu C.-Y. Huang V. Percec R.G. Petschek C. Rosenblatt 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(2):251-255
Magnetic and electrical Freedericksz measurements were performed on the second generation monodendritic liquid crystal G2(OH). The deduced elastic constants were found to be exceptionally anisotropic: the splay elastic constant K11 is more than an order of magnitude larger than the bend elastic constant K33, and the twist constant K22 is approximately twice K33. The results are discussed in terms of molecular conformations.
Received: 23 February 1998 / Revised and Accepted: 26 May 1998 相似文献
2.
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
3.
Increasing rewriting speed of optical rewritable e-paper by selecting proper liquid crystals
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Effect of interaction between liquid crystal (LC) and photoalignment material on speed of optical rewriting process is investigated. The theoretical analysis shows that smaller frank elastic constant K22 of liquid crystal corresponds to larger twist angle, which gives rise to larger rewriting speed. Six different LC cells with the same boundary conditions (one substrate is covered with rubbed polyimide (PI) and other with photo sensitive rewritable sulfuric dye 1(SD1)) are tested experimentally under the same illumination intensity (450 nm, 80 mW/cm2). The results demonstrate that with suitable liquid crystal, LC optical rewriting speed for e-paper application can be obviously improved. For two well known LC materials E7 (K22 is larger) and 5CB (K22 is smaller), they require 11 s and 6 s corresponding to change alignment direction for generating image information. 相似文献
4.
Min Pan Zheng Huang HuanFeng Ma WeiRong Qiang LianFu Wei Long Wang Yong Zhao 《中国科学G辑(英文版)》2009,52(7):993-996
The lattice parameters, band structure, density of state and elastic constant of RE-doped CeO2 (RE=Sm, Gd, Dy), the buffer material for coated HTS conductors, are calculated using the plane-wave method with pseudopotentials
based on the density functional theory (DFT) of first-principle. The rule and mechanism of the effect of rare earth impurity
on the critical thickness of the CeO2 buffer layer are investigated. It is found that, in the range of the calculation, the changes of the lattice volume V and elastic constant E* of CeO2 with the impurity are mainly determined by the increased electrons δn
e of the system. The relationship of the elastic constant E* and increased electrons δn
e is established. It is indicated that the critical thickness of the CeO2 single buffer layer doped with Sm, Gd, and Dy may be enhanced by 22%, 43% and 33%, respectively.
Supported by the Youth Scientific Research Project of Southwest Jiaotong University (Grant No. 2007Q017), the National Natural
Science Foundation of China (Grant No. 50588201), and the Ministry of Science and Technology of China (Grant No. 2007CB616906) 相似文献
5.
A critical twist angle, above which twist can relax homogeneously, has been observed in the liquid crystals MBBA and 5CB. The results suggest that (2K22 ? K33) increases through zero on heating and at Tc becomes equal to K11. 相似文献
6.
A. V. Semirov D. A. Bukreev V. O. Kudryavtsev A. A. Moiseev A. A. Gavrilyuk A. L. Semenov G. V. Zakharov 《Technical Physics》2009,54(11):1586-1590
The effect of temperature and elastic tensile stresses on the magnetoimpedance of an amorphous Vitrovac 6025Z (Fe4CO67Mo1.5Si16.5B11) foil is studied. Two temperature ranges (20–70 and 70–220°C) in which the effect of elastic tensile stresses on the magnetoimpedance
has different characters are detected. The existence of these two temperature ranges is shown to be caused by a change in
the sign of a magnetostriction constant at 70°C. 相似文献
7.
The structural, mechanical, electronic and thermoelectric properties of the low temperature orthorhombic perovskite phase of CH3NH3PbI3 have been investigated using density functional theory (DFT). Elastic parameters bulk modulus B, Young’s modulus E, shear modulus G, Poisson’s ratio ν and anisotropy value A have been calculated by the Voigt–Reuss–Hill averaging scheme. Phonon dispersions of the structure were investigated using a finite displacement method. The relaxed system is dynamically stable, and the equilibrium elastic constants satisfy all the mechanical stability criteria for orthorhombic crystals, showing stability against the influence of external forces. The lattice thermal conductivity was calculated within the single-mode relaxation-time approximation of the Boltzmann equation from first-principles anharmonic lattice dynamics calculations. Our results show that lattice thermal conductivity is anisotropic, and the corresponding lattice thermal conductivity at 150 K was found to be 0.189, 0.138, and 0.530 Wm?1K?1 in the a, b, and c directions. Electronic structure calculations demonstrate that this compound has a DFT direct band gap at the gamma point of about 1.57 eV. The electronic transport properties have been calculated by solving the semiclassical Boltzmann transport equation on top of DFT calculations, within the constant relaxation time approximation. The Seebeck coefficient S is almost constant from 50 to 150 K. At temperatures 100 and 150 K, the maximal figure of merit is found to be 0.06 and 0.122 in the direction of the c-axis, respectively. 相似文献
8.
V. G. Kytin B. M. Bulychev A. V. Krechetov E. A. Konstantinova V. A. Kulbachinskiĭ R. A. Lunin 《Journal of Experimental and Theoretical Physics》2007,105(1):250-252
A series of new heterofullerides with compositions Rb2MC60, K2MC60, and KM2C60 (M = Mg, Be) have been synthesized. Measurements of the temperature dependences of the magnetic susceptibility in the temperature interval from 4.2 to 300 K reveal a superconducting transition in heterofullerides K2MgC60, KMg2C60, K2BeC60, and Rb2BeC60 at temperatures T c = 13–22 K. The electron states with uncompensated spin are studied by the electron paramagnetic resonance technique. The contributions of conduction electrons and localized electrons to the paramagnetic susceptibility are extracted. 相似文献
9.
Polymer composite comprising polyvinylidene fluoride (PVDF) and potassium hexatitante (K2Ti6O13) was synthesized by solution casting. The effect of K2Ti6O13 on surface, thermal, and electrical properties of polymer composite were investigated. The addition of K2Ti6O13 with polymer leads to thermal degradation and transition of polymer composite from semi-crystalline to amorphous phase. The optimum results of contact angle for different loading wt% of K2Ti6O13 were directly correlated with the surface morphology. Our experimental results confirmed the incorporation of K2Ti6O13 in polymer by SEM micrographs. The evaluated dielectric properties (ε' = 424; tan δ = 2.14 at 130 °C and 100 Hz frequency for 20 wt% loading of K2Ti6O13) for polymer composite are higher in compared to pure polymer. The enhancement in dielectric constant and changing the surface properties of polymer composite can be used for the development of electrochemical storage device applications. 相似文献
10.
K. Araki T. Goto Y. Nemoto T. Yanagisawa B. Lüthi 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(3):257-259
The temperature dependence of the elastic constants in
Tb3Ga5O12 was measured and analysed with a simple crystal
field model. The magneto-elastic coupling constants have been deduced from
this experiment. The coupling constant gΓ5, related to the
c44 mode, is anomalously large. These coupling constants are important
for the interpretation of the phonon Hall effect. 相似文献
11.
In G-rich DNA, it is well known that the form changes from single-strand DNA to G-quadruplex due to cations. In this study, we analyze the diffusion coefficient and fluorescence intensity obtained by fluorescence correlation spectroscopy for short G-rich DNA of the (G3T1)4 sequence labeled as 5-Carboxytetramethylrhodamine (TAMRA) with variation of the K+ ion concentration. At a K+ ion concentration of more than 200 mM, the single-strand DNA was changed to the G-quadruplex. The size of the G-quadruplex decreased to 86% than the size of the single strand DNA at K+ ion concentration of 0 M. The size of the G-quadruplex and the fluorescence intensity of TAMRA attached to the DNA were constant with an increase in the K+ ion concentration between 200 and 800 mM. This means that the size of the DNA and the fluorescence intensity of the TAMRA are not affected by the K+ ion concentration at the G-quadruplex structure because the binding structure of DNA and TAMRA dye leads to stability at a concentration of less than 100 mM K+. Based on our short G-rich DNA results, longer G-rich DNA is analyzed for the diffusion coefficient of the DNA and the fluorescence intensity variation of fluorescence dye attached to the DNA. 相似文献
12.
《Current Applied Physics》2010,10(2):561-564
The viscoelastic parameters of nematic liquid crystal (LC) E7 in both splay and twist relaxation modes are investigated as functions of pretilt angle and temperature by the technique of dynamic laser light scattering. The results show that the elastic constants of the liquid crystal in the two modes not only depend on temperature, but also depend on pretilt angle. There is a critical pretilt angle (βC) at which nematic LC begins exhibiting elastic property, and beyond which the elastic constants increase with pretilt angle, then keep constant after exceeding another angle (βS, with βS > βC). This phenomenon is observed to be universal for different nematic LC’s, and significant not only in the understanding of the molecular mechanism of exhibiting viscoelastic properties in nematic LC, but also for their practical purpose. 相似文献
13.
A. Bouhemadou Y. Al-Douri R. Khenata K. Haddadi 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,71(2):185-194
We have investigated the structural, elastic, electronic, optical and
thermal properties of c-SiGe2N4 by using the ultrasoft
pseudopotential density functional method within the generalized gradient
approximation. The calculated structural parameters, including the lattice
constant, the internal free parameter, the bulk modulus and its pressure
derivative are in agreement with the available data. The independent elastic
constants and their pressure dependence, calculated using the static finite
strain technique, satisfy the requirement of mechanical stability,
indicating that c-SiGe2N4 compound could be stable. We derive the
shear modulus, Young’s modulus, Poisson’s ratio and Lamé’s coefficients
for ideal polycrystalline c-SiGe2N4 aggregate in the framework of
the Voigt-Reuss-Hill approximation. We estimate the Debye temperature of
this compound from the average sound velocity. Band structure, density of
states, Mulliken charge populations and pressure coefficients of energy band
gaps are investigated. Furthermore, in order to understand the optical
properties of c-SiGe2N4, the dielectric function, refractive index,
extinction coefficient, optical reflectivity and electron energy loss are
calculated for radiation up to 40 eV. Thermal effects on some macroscopic
properties of c-SiGe2N4 are predicted using the quasi-harmonic
Debye model in which the lattice vibrations are taken into account. We have
obtained successfully the variations of the primitive cell volume, volume
expansion coefficient, heat capacities and Debye temperature with pressure
and temperature in the ranges of 0–40 GPa and 0–2000 K. For the first
time, the numerical estimates of the elastic constants and related
parameters, and the thermal properties are performed for
c-SiGe2N4. 相似文献
14.
E. N. Sheftel’ S. V. Komogortsev R. S. Iskhakov P. K. Sidorenko L. A. Chekanova N. S. Perov A. N. Ivanov 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(10):1449-1451
The magnetic properties (magnetization curve, ferromagnetic resonance spectrum) of nanocrystalline Fe79Zr10N11 films obtained by RF magnetron sputtering with subsequent annealing were studied experimentally, along with the fundamental
magnetic constants of these films (saturation magnetization M
S, local magnetic anisotropy energy K, and the exchange coupling constant A). The magnetic properties are discussed within the random magnetic model, which determines the correlation of the magnetic
properties with the fundamental magnetic constants and nanostructure parameters (grain size, magnetic anisotropy, and correlation
radius R
C). The exchange correlation length 2R
L
for the film magnetic microstructure was determined by correlation magnetometry. 相似文献
15.
A. K. Radzhabov E. V. Charnaya B. Mroz C. Tien Z. Tylczynski C. -S. Wur 《Physics of the Solid State》2004,46(4):775-779
Ultrasonic studies of the temperature behavior of the velocity and damping of sound for the xx and zz longitudinal and yx and zx transverse waves in K3Na(CrO4)2 have been carried out in the temperature interval 185–295 K, which includes the region of the ferroelastic phase transition. The acoustic parameters for both shear and longitudinal waves were found to have anomalies in the region of the phase transition with a Curie temperature of 235.5 K. A theoretical analysis of the softening of the elastic moduli c44 and c66 was performed on the basis of the Landau expansion in terms of the strain tensor components ?4 and (?2-?1)/2 considered as the linearly coupled primary and secondary order parameter, respectively. The absolute values of the elastic moduli c11, c33, c44, c66, c12, and c14 at 295 K were calculated. 相似文献
16.
V. Yu. Topolov 《Physics of the Solid State》2003,45(7):1295-1297
A new model of the elastic matching of phases is proposed, and heterophase structures near the morphotropic phase boundary in 0.10PbTiO3-0.90Pb(Zn1/3Nb2/3)O3 crystals are studied. Unique behavior of the unit cell parameters is found to favor the elastic matching of the ferroelectric tetragonal and orthorhombic phases under the conditions of complete or partial relaxation of internal mechanical stresses at a volume concentration ratio of these phases of about 20/80% and temperatures of T=20–300 K. Interrelations between the volume concentrations of different domain (twin) types and of the coexisting phases are analyzed. 相似文献
17.
C.S. O'Hern R.D. Kamien T.C. Lubensky P. Nelson 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(1):95-102
We present an elastic model of B-form DNA as a stack of thin, rigid plates or base pairs that are not permitted to deform.
The symmetry of DNA and the constraint of plate rigidity limit the number of bulk elastic constants contributing to a macroscopic
elasticity theory of DNA to four. We derive an effective twist-stretch energy in terms of the macroscopic stretch along and relative excess twist about the DNA molecular axis. In addition to the bulk stretch and twist moduli found previously, we obtain a twist-stretch
modulus with the following remarkable properties: 1) it vanishes when the radius of the helical curve following the geometric
center of each plate is zero, 2) it vanishes with the elastic constant K23 that couples compression normal to the plates to a shear strain, if the plates are perpendicular to the molecular axis, and
3) it is nonzero if the plates are tilted relative to the molecular axis. This implies that a laminated helical structure
carved out of an isotropic elastic medium will not twist in response to a stretching force, but an isotropic material will twist
if it is bent into the shape of a helix.
Received: 4 July 1997 / Received in final form: 16 October 1997 / Accepted: 21 October 1997 相似文献
18.
The magnetic susceptibility, heat capacity, and spin-spin correlation functions of manganese oxide Pb3Mn7O15 are calculated by the Monte Carlo method. Two critical temperatures are determined: T 1 ≈ 20 K, above which a modulated structure along the hexagonal axis is formed, and T 2 ≈ 70 K, at which the long-range magnetic order disappears. The antiferromagnetic exchange interaction constant in a hexagonal plane is estimated to be J 1 ~ 7 K, and the antiferromagnetic and ferromagnetic exchange interaction constants between hexagonal planes are calculated to be J 2 ~ 3 K and K ~ 50 K, respectively. 相似文献
19.
Features of spin exchange in nitroxide biradicals in the ionic liquid bmimPF<Subscript>6</Subscript>
V. A. Tran Aleksandr I. Kokorin G. Grampp K. Rasmussen 《Applied magnetic resonance》2009,35(3):389-398
The intramolecular electron spin exchange has been studied by electron paramagnetic resonance (EPR) spectroscopy in the ionic
liquid 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6) for various nitroxide biradicals as a function of temperature and the nature of the connecting bridge between two >NO· centers. Temperature variations of the isotropic nitrogen hyperfine splitting constant a and exchange integral values |J/a| were measured from EPR spectra and analyzed. Thermodynamic parameters of the conformational rearrangements were obtained.
The spin exchange in rigid and flexible biradicals dissolved in the ionic liquid bmimPF6 was compared with that in toluene solutions. Interesting features of the spin exchange in biradicals in ionic liquid were
observed and explained as a result of the specific intramolecular conformational transitions. The first example of a rather
rigid biradical molecule becoming flexible under the influence of an ionic liquid is reported. 相似文献
20.
G. A. Komandin A. S. Prokhorov V. I. Torgashev E. S. Zhukova B. P. Gorshunov A. A. Bush 《Physics of the Solid State》2011,53(4):736-744
The spectra of complex permittivity of a Ba2Mg2Fe12O22 single crystal belonging to the family of Y-type hexaferrites have been measured over a wide temperature range (10–300 K) with the aim of determining the dynamic parameters
of the phonon and magnetic subsystems in the terahertz and infrared frequency ranges (3–4500 cm−1). A factor-group analysis of the vibrational modes has been performed, and the results obtained have been compared with the
experimentally observed resonances. The oscillator parameters of all nineteen phonon modes of E
u
symmetry, which are allowed by the symmetry of the Ba2Mg2Fe12O22 crystal lattice, have been calculated. It has been found that, at temperatures below 195 and 50 K, the spectral response
exhibits new absorption lines due to magnetic excitations. 相似文献