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1.
The depolarisation ratio for the Raman-active phenyl stretching mode has been measured over the whole of the mesophase range,
and the orientational order parameters deduced, in the uniaxial nematic liquid crystal octylcyanobiphenyl (8CB). Linearly
polarised light was incident normally on a homogeneously aligned sample and a χ2 minimisation routine performed on the 360° depolarisation ratio profile. The order parameters 〈P
200〉 and 〈P
400〉 , together with the differential polarisability ratio, r , are used as fitting parameters and measured as a function of temperature. Interestingly, we show that the value for r , conventionally measured in the isotropic phase and assumed to remain constant, has a clear temperature dependence, ranging
from -0.032±0.008 in the isotropic phase through to -0.245±0.015 at the nematic-to-smectic A phase transition. The measured
order parameters 〈P
200〉 and 〈P
400〉 varied from 0.35- 0.55±0.02 and 0.180- 0.245±0.02 , respectively, across the 8 ° C wide nematic phase range. The values of both 〈P
200〉 and 〈P
400〉 are in excellent agreement with theory, but it is noteworthy that 〈P
400〉 shows a much better quantitative match than has been reported in previous work. Crucially the temperature dependence of
r is shown to be a contributing factor in the low 〈P
400〉 values that have been conventionally reported from Raman scattering measurements. The potential for fitting the entire angular
depolarisation ratio distribution in liquid crystalline systems that are described by more order parameters, specifically
biaxial materials, is discussed. 相似文献
2.
N. K. Deepak 《Pramana》2010,74(3):421-440
The channelling and scattering yields of 1 MeV α-particles in the 〈100〉, 〈110〉 and 〈111〉 directions of silicon implanted with bismuth and ytterbium have been simulated using
N-body model. The close encounter yield from dopant atoms in silicon is determined from the flux density, using the Bontemps
and Fontenille method. All previous works reported in literature so far have been done with computer programmes using a statistical
analytical expression or by a binary collision model or a continuum model. These results at the best gave only the transverse
displacement of the lattice site from the concerned channelling direction. Here we applied the superior N-body model to study the yield from bismuth in silicon. The finding that bismuth atom occupies a position close to the silicon
substitutional site is new. The transverse displacement of the suggested lattice site from the channelling direction is consistent
with the experimental results. The above model is also applied to determine the location of ytterbium in silicon. The present
values show good agreement with the experimental results. 相似文献
3.
The redistribution of the electronic polarization in deuterium atoms is analyzed theoretically and the various polarization
moments are shown to influence the magnetic resonance signal of deuterium. The analysis gives expressions that relate the
amplitudes of the magnetic resonance signals for various Zeemann sublevels of the D atom to the electronic and nuclear polarizations
of these atoms and their nuclear alignment. Experimental data on the optical orientation and spin exchange in a D-Cs mixture
are used to determine the electronic and nuclear orientation and nuclear alignment of the D atoms, which are found to be 〈S
z〉=0.1, 〈I
z〉=0.27, and 〈Q
zz=0.027.
Zh. Tekh. Fiz. 67, 22–26 (January 1997) 相似文献
4.
S N Vaidya 《Pramana》1979,12(1):23-32
A theory of melting based on vacancy model is formulated. The polymer solution theory is used for derivation of the melting
equation for a two-species model of melting solid. Under simplifying assumptions the analysis leads to a simple correlation
betweenT
m and 〈v〉, the average energy of interaction between the vibrating atoms. Pseudopotential method is used for calculating 〈v〉 for the alkali metals lithium, sodium, potassium and rubidium at temperatureT
m. The calculated values ofT
m〈v〉 are in accord with those expected from our model. Application to the high pressure melting curves of solids is also discussed. 相似文献
5.
Michael O’Carroll 《Journal of statistical physics》2012,146(4):864-869
We consider general d-dimensional lattice ferromagnetic spin systems with nearest neighbor interactions in the high temperature region (β≪1). Each model is characterized by a single site apriori spin distribution taken to be even. We also take the parameter α=〈s
4〉−3〈s
2〉2>0, i.e. in the region which we call Gaussian subjugation, where 〈s
k
〉 denotes the kth moment of the apriori distribution. Associated with the model is a lattice quantum field theory known to contain a particle
of asymptotic mass −lnβ and a bound state below the two-particle threshold. We develop a β analytic perturbation theory for the binding energy of this bound state. As a key ingredient in obtaining our result we show
that the Fourier transform of the two-point function is a meromorphic function, with a simple pole, in a suitable complex
spectral parameter and the coefficients of its Laurent expansion are analytic in β. 相似文献
6.
Wenwei Ge Hong Liu Xiangyong Zhao Xiaobing Li Xiaoming Pan Di Lin Haiqing Xu Xiangping Jiang Haosu Luo 《Applied Physics A: Materials Science & Processing》2009,95(3):761-767
In this paper, a single crystal of 0.96Na0.5Bi0.5TiO3-0.04BaTiO3 with dimensions of Φ 30×10 mm was grown by the top-seeded-solution growth method. X-ray powder diffraction results show that the as-grown crystal
possesses the rhombohedral perovskite-type structure. The dielectric, piezoelectric and electrical conductivity properties
were systematically investigated with 〈001〉, 〈110〉 and 〈111〉 oriented crystal samples. The room-temperature dielectric constants
for the 〈001〉, 〈110〉 and 〈111〉 oriented crystal samples are found to be 650, 740 and 400 at 1 kHz. The (T
m, ε
m) values of the dielectric temperature spectra are almost independent of the crystal orientations; they are (306°C, 3718),
(305°C, 3613) and (307°C, 3600) at 1 kHz for the 〈001〉, 〈110〉 and 〈111〉 oriented crystal. The optimum poling conditions were
obtained by investigating the piezoelectric constants d
33 as a function of poling temperature and poling electric field. For the 〈001〉 and 〈110〉 crystal samples, the maximum d
33 values of 146 and 117 pC/N are obtained when a poling electric field of 3.5 kV/mm and a poling temperature of 80°C were applied
during the poling process. The as-grown 0.96Na0.5Bi0.5TiO3-0.04BaTiO3 crystal possesses a relatively large dc electrical conductivity, especially at higher temperature, having a value of 1.98×10−11 Ω−1⋅m−1 and 3.95×10−9 Ω−1⋅m−1 at 25°C and 150°C for the 〈001〉 oriented crystal sample. 相似文献
7.
Sugui Tian Yong Su Lili Yu Huichen Yu Shu Zhang Benjiang Qian 《Applied Physics A: Materials Science & Processing》2011,104(2):643-647
Microstructure of [011] oriented single crystal nickel-base superalloy consists of the cubical γ′ phase embedded coherently in the γ matrix, and arranged regularly along 〈100〉 orientations. After tensile creep, the cubical γ′ phase in the alloy is transformed into the strip-like rafted structure along [001] direction under the ordering transformation
free-energy and strain energy change. And the directional growing of γ′ phase is attributed to the atoms Al and Ta into (001) plane to form the stable stacking mode. 相似文献
8.
K. Heilig 《Hyperfine Interactions》1987,38(1-4):803-816
The changes of the mean-square nuclear charge radii have been re-evaluated [3] on an equivalent basis, using all available
data from optical spectroscopy. The steps of evaluation are discussed and the results are presented in a number of diagrams,
showing the course of 〈r
2〉 fromN=20 toN=152 and showing details of δ〈r
2〉 相似文献
9.
The method of transmission electron microscopy is used to study the dislocation structure in single crystals of the Ni
3
Fe ordered alloy for different degrees of strain. The [1812], [011], [111] and [001] single crystal orientations are examined.
The superdislocation splitting (r) is measured for different degrees of strain, distributions of r are constructed, and their
average values 〈r〉 are estimated. The 〈r〉-ε curves are constructed. With the use of the experimental r values, the effective
energy of antiphase boundaries ζ* is estimated.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 51–56, January, 2006. 相似文献
10.
O. A. Dushina V. M. Molochnikov A. A. Paereliy N. I. Mikheev V. V. Lemanov 《Thermophysics and Aeromechanics》2010,17(3):323-335
The PIV technique was used to measure the instantaneous vector fields of flow velocity and vorticity behind a thin cross-flow
rib installed in a channel with laminar, transient, or turbulent flow. The data were treated statistically to determine the
fields of mean longitudinal flow velocity and the correlations of pulsating velocity components 〈u′ν′〉 and 〈u′u′〉. Some features of the flow structure developing under conditions of laminar-turbulent transition behind the rib have been
revealed. 相似文献
11.
Theoretical expressions of 〈y
N〉, 〈|y
N − σ1
y
P
c
|〉 and 〈|y
N
2
−σ
1
2
(y
P
c
)2|〉 (wherey
N andy
P
c
are the normalized structure amplitudes of the structure and the model respectively) are derived in terms of the heavy atom
contributionσ
1
2
for monoclinic and orthorhombic crystals containing a few (i.e., 1 or 2) heavy atoms of the same kind per asymmetric unit by taking the heavy atom part alone as the model. Results are obtained
for both the related and unrelated cases. The local values of 〈y
N〉 and 〈|y
N
n
− σ
1
n
(y
P
c
)
n
|〉, (n=1, 2) calculated from these expressions can be used to calculate the overall values of the conventionalR-indicesR(F) andR(I) for the related and unrelated cases. These overall values could be used to check the correctness of heavy atoms located
in the structure.
Contribution No. 550 相似文献
12.
The possibility of resonance during elastic intravalley scattering in n-type semiconductors is investigated in connection with the crossing (due to anisotropy of the effective mass) of the energy
levels of excited states of a shallow donor as functions of the magnetic field. The hybridization of states of different frequencies
in the vicinity of a crossing is attributed to the emergence of a nonzero dipole moment of the excited impurity atom and,
accordingly, a long-range potential, which creates carrier-transport anomalies. The lower part of the donor spectrum is calculated
as a function of the magnetic field in Si with B∥〈001〉 and in Ge with B∥〈111〉 or B∥〈110〉. A crossing occurs in Ge in the field range 9.9 T<B<16.7 T and in Si in the field range 10.5 T<B<37.7 T. The characteristic longitudinal relaxation time and the transverse conductivity, which are determined by scattering
at excited donors in the presence of the hybridization of states, are calculated.
Zh. éksp. Teor. Fiz. 112, 975–1010 (September 1997) 相似文献
13.
We investigate numerically and analytically the statistics of Markov chains on so-called braid (B
n
) and locally free (ℒℱ
n
) groups. Namely, we compute the mean length 〈μ〉 and the variance 〈μ2〉−〈μ〉2 of the shortest word which remains after applying of all group relations to the randomly generatedN-letter word (Markov chain). We express the conjecture (numerically justified) that the mean value 〈μ〉 for the random walk
on the groupB
n
(n≫1) coincides with high accuracy with the same value for the random walk on the “locally free group weth errors” if the number
of errors is of order of 20%. 相似文献
14.
D. M. Sedrakyan D. A. Badalyan V. M. Gasparyan A. Zh. Khachatryan 《Journal of Experimental and Theoretical Physics》1997,84(2):317-321
We find the dependence of the ensemble-averaged resistance, 〈ρ
L〉, of a one-dimensional chain consisting of periodically spaced random delta-function potentials of the chain length L, the incident-electron energy, and the chain disorder parameter w. We show that generally the 〈ρ
L〉 vs L dependence can be written as a sum of three exponential functions, two of which tend to zero as L℩∞. Hence the asymptotic expression for 〈ρ
L〉 is always an exponential function of L. Such an expression for 〈ρ
L〉 means that the electronic states are indeed localized and makes it possible (which is important) to find the dependence
of the localization radius on the incident-electron energy and the force with which an electron interacts with the sites of
the chain. We also derive a recurrence representation for 〈ρ
L〉, which proves convenient in numerical calculations.
Zh. éksp. Teor. Fiz. 111, 575–584 (February 1997) 相似文献
15.
The study reported in this paper contributes to better understanding the thermal oxidation effect on structural and optical
properties of polycrystalline silicon heavily in situ P-LPCVD films. The deposits, doped at levels 3×1019 and 1.6×1020 cm−3, have been elaborated from silane decomposition (400 mTorrs, 605°C) on monosilicon substrate oriented 〈111〉. The thermal
oxidation was performed at temperatures: 850°C during 1 hour, 1000, 1050, and 1100°C during 15 minutes. The XRD spectra analysis
pointed out significant 〈111〉 texture evolution, while in the case of 〈220〉 and 〈311〉 textures, the intensities are practically
invariant (variations fall in the uncertainty intervals). The optical characterizations showed that refractive index and absorption
coefficient are very sensitive to the oxidation treatment, mainly when the doping level is not very high. We think that atomic
oxygen acts as defects passivating agent leading to carriers’ concentration increasing. Besides, the optical behavior is modeled
in visible and near infrared, by a seven-term polynomial function n
2=f(λ
2), with alternate signs, instead of theoretically unlimited terms number from Drude’s model. It has been shown that fitting
parameters fall on Gaussian curves like they do in the theoretical model. 相似文献
16.
Summary The turbulent hydrodynamic diffusion may essentially change the kinetics of the elementary chemical reactions. The much faster
character of the turbulent diffusion and the evolution of the relative displacements of particles in the inertial range according
to the Richardson law, 〈Δr
2〉 ∞t
3, rather than 〈Δr
2〉 ∞t, remove in many cases the ?bottleneck? effects created by the molecular diffusion and seriously influences the diffusioncontrolled
processes. It changes also the Debye screening of the charged particles in the turbulent fluids and the scenario of the Turing
instability. These problems are discussed in our paper. The consideration is based and on the Obukhov's suggestion on the
Markovian character of evolution of liquid particles in turbulent flows. The role of non-Markovian corrections is also briefly
discussed.
To speed up pubblication, the authors of this paper have agreed to not receive the proofs for correction. 相似文献
17.
An expression for the fourth moment of the line profile in terms of several strain derivatives and the possibility of measuring
the ‘wavelength’ of crystal distortions (λ) for any sinusoidally varying component of the strain are available. The experimental means for evaluating such strain derivatives
in the expression for the fourth moment was earlier described. A numerical method for evaluating this wavelength and its subsequent
use to determineλ in several samples ofα-brass is presented here. The data used are taken from the earlier paper of the authors. An attempt has been made to interpret
the values ofλ and their changes with cold working and annealing in terms of lattice strain. 相似文献
18.
Devraj Singh Dharmendra K. Pandey Pramod K. Yadawa 《Central European Journal of Physics》2009,7(1):198-205
The ultrasonic attenuation in thulium monochalcogenides TmX (X=S, Se and Te) has been studied theoretically with a modified Mason’s approach in the temperature and range 100 K to 300 K
along 〈100〉, 〈110〉 〈111〉 crystallographic directions. The thulium monochalcogenides have attracted a lot of interest due to
their complex physical and chemical characteristics. TmS, TmSe and TmTe are trivalent metal, mixed valence state, and divalent
semiconductor, respectively. Coulomb and Born-Mayer potential is applied to evaluate the second- and third-order elastic constants.
These elastic constants are used to compute ultrasonic parameters such as ultrasonic velocities, thermal relaxation time,
and acoustic coupling constants that, in turn, are used to evaluate ultrasonic attenuation. A comparison of calculated ultrasonic
parameters with available theoretical/experimental physical parameters gives information about classification of these materials.
相似文献
19.
P. Zh. Aslanyan V. N. Emelyanenko G. G. Rikhkvitzkaya 《Physics of Particles and Nuclei Letters》2007,4(1):60-66
The experimental data from the 2-m propane bubble chamber have been analyzed for pC → Λ(K
s
0
)X reactions at 10 GeV/c. The estimation of experimental inclusive cross sections for Λ and K
s
0
production in the p
12C collision is equal to σΛ = (13.3 ± 1.7) mb and σ
K
s
0
= (4.6 ± 0.6) mb, respectively. The measured 〈Λ〉/〈π+〉 ratio from pC reaction is equal to (5.3 ± 0.8) × 10−2, and it is approximately two times larger than the 〈Λ〉/〈π+〉 ratio simulated by the FRITIOF model and than that of experimental pp reactions at the same energy.
The text was submitted by the authors in English. 相似文献
20.
Using the appropriate harmonic oscillator states and reasonable approximations, we construct coherent wavepackets corresponding
to the solutions of the Klein-Gordon equation for the attractive potentialV(r)=−k/r, k>0, in two and three space dimensions. We deduce the corresponding classical limit in two dimension by requiring that the
expectation value 〈r〉 of the radial variable is large. In the case of three dimensions, besides the condition of large 〈r〉, we make the uncertainty Δr=[〈r
2〉 − 〈r〉2]1/2 a minimum with respect to certain parameter of the wavepacket. We then investigate the trajectory traversed by the wavepacket
in the classical limit. We find that the classical limit of this relativistic quantal problem gives, in the leading order,
the same expression for the rate of motion of the perihelion as that given by the solution of the corresponding special relativistic
classical dynamical problem. We also briefly discuss some of the subtle aspects of the classical limit of the relativistic
quantal system, in general. 相似文献