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1.
The joint probability density functions of the normalized structure amplitudes of the structure and the model (i.e.,y
N andy
p
c
) are derived for triclinic crystals containing heavy atoms (1, 2 and many) by taking the model to consist of the heavy atoms
and a part of the light atoms in the unit cell. These functions are derived for the two cases where the model is completely
correct (i.e., the related case) and where the model is completely wrong (i.e., the unrelated case) in terms of the fractional contributions to the local mean intensity from the heavy atoms and all known
atoms (i.e., σ
1h
/2
and σ
1
2
) as parameters. These functions are then used to obtain the theoretical local values of 〈y
N〉 and 〈|y
N
n
− σ
1
n
(y
P
c
)
n
|〉,n=1, 2. A method of using these results to compute the theoretical overall values ofR(F) andR(I) for the related and unrelated cases is briefly described. A comparison of the observed values of these indices with their
theoretical values for the related and unrelated cases would help in determining the correctness of the proposed trial structure.
Contribution No. 548 相似文献
2.
Measurements have been made of the Hall coefficientR of some alloys of silver in palladium over the temperature range 1°K to 120°K. The alloys contain between ∼1 and ∼10 at.-%
silver. Values ofR were also obtained at room temperature and these were in good agreement with earlier published work. The values ofR are negative in all the alloys, and |R| increases both on reducing the temperature and increasing the silver concentration,c. Below ∼10°K, |R| becomes independent of temperature but shows a linear dependence onc, increasing by a factor of 2.5 over the concentration range measured.
This increase is too great to be accounted for in terms of band structure changes alone, so we have examined the effects of
anisotropic impurity scattering. To a first approximation it can be shown thatR is proportional to an anisotropy parameterA, defined asA=〈τ
2(k)〉/〈τ(k)〉2, whereτ(k) represents the relaxation time of an electron in a statek, and 〈〉 is an average over the Fermi surface. In palladium we assume that the majority of the current is carried by the s-electrons.
In the presence of silver impurities these electrons can be scattered into s-states or d-states with relaxation times given
byτ
ss
α1/c(1−c) andτ
sd
α1/c
2(1−c) respectively. FollowingPlate we have assumed thatτ
ss is isotropic and thatτ
sd is anisotropic, leading to an overall anisotropic relaxation time for impurity scattering. We then find the parameterA increases approximately linearly with silver content, in accordance with our experimental results. 相似文献
3.
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
4.
M. I. Daunov I. K. Kamilov A. B. Magomedov 《Journal of Experimental and Theoretical Physics》1997,84(2):309-316
We use the data on the pressure (up to P=1.5 GPa) and field (up to H=17 kOe) dependence of the Hall coefficient and the resistivity at 77.6 and 300 K in p-CdSnAs2〈Cu〉 to calculate the effective kinetic characteristics of the charge carriers, the density and mobility of the conduction
electrons and the holes of the deep acceptor and valence bands, in an interval of excess-acceptor densities N
ext ranging from 1010–1017 cm−3. We establish that in a heavily doped semiconductor with a deep impurity band at the tail of the density of states of the
intrinsic band, with unequal donor and acceptor densities, a a heavily doped and fully compensated semiconductor state is
realized under hydrostatic compression. The threshold value of the pressure that initiates the transition into such a state,
P
c, depends on the extent to which the impurity band is populated. In p-CdSnAs2〈Cu〉 at N
ext=N
A, where N
A is the density of deep acceptors, and T⩽77.6 K the value of P
c amounts to 10−4 GPa. As the population of the deep acceptor band grows, P
c increases and in the limit becomes infinite. We discuss the special features of the electrophysical properties of p-CdSnAs2〈Cu〉 arising from the absence of an energy gap between the states of the conduction band and those of the deep acceptor band.
Zh. éksp. Teor. Fiz. 111, 562–574 (February 1997) 相似文献
5.
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
6.
An electron paramagnetic resonance (EPR) line shape simulation for nitroxide spin probes in the motional narrowing region
was carried out assuming axially symmetricg andA tensors and with different anisotropies of rotationN (=R
∥/R
⊥) whereR
∥ andR
⊥ are, respectively, elements of the diffusion tensor along and perpendicular to its principal axisz′. In addition, it was assumed that the principal axes of the diffusion tensor coincide with the molecular axes. Each of three
casesz′=x,z′=y andz′=z, which result from cyclic permutations of the molecular axesx, y andz with thez′,y′ andx′ axes of the diffusion tensor, yields its typical EPR spectrum characterized by the relative intensities of the low-, center-
and high-field lines. The parameter δ defined by and calculable from the intensities of the three lines was found to vary
linearly withN for thez′=x andz′=y cases and, as anticipated, to be practically constant at a value of 1 for thez′=z case. This suggested a method for estimatingN for a probe from its EPR spectrum. Experimental spectra over a narrow temperature range (1°C) in the vicinity of the nematic-to-isotropic
transition (about 34.6°C) ofN-(4-n-butylbenzilidene)-4-amino-2,2,6,6-tetramethylpiperidine-1-oxide at a mole fraction of 1·10−3 in 4-n-pentyl-4′-cyanobiphenyl showed a pattern of peak heights characteristic of thez′=x case with δ values that gave, neglecting effects of the mean field, higher and lowerN values in the nematic and isotropic regions, respectively. Analysis of other similar systems in the literature gave similar
results. 相似文献
7.
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
8.
J. K. Baria 《Czechoslovak Journal of Physics》2004,54(4):469-485
A model pseudopotential depending on an effective core radius but otherwise parameter free is used to study the interatomic
interactions, phonon dispersion curves (inq and r-space analysis), phonon density of states, mode Grüneisen parameters, dynamical elastic constants (C
11,C
12 andC
44), bulk modulus (B), shear modulus (C′), deviation from Cauchy relation (C
12–C
44), Poisson’s ratio (σ), Young’s modulus (Y), behavior of phonon frequencies in the elastic limit independent of the direction (Y
1), limiting value in the [110] direction (Y
2), degree of elastic anisotropy (A), maximum frequencyω
max, mean frequency 〈ω〉, 〈ω
2〉1/2=(〈ω〉/〈ω
−1〉)1/2, fundamental frequency 〈ω
2〉, and propagation velocities of the elastic constants in Cu, Ag, Au, Ni, Pd, and Pt. The contribution of s-like electrons
is calculated in the second-order perturbation theory for the model potential while that of d-like electrons is taken into
account by introducing repulsive short-range Born-Mayer like term. Very recently proposed screening function due to Sarkar
et al. has been used to obtain the screened form factor. The theoretical results are compared with experimental findings wherever
possible. A good agreement between theoretical investigations and experimental findings has proved the ability of our model
potential for predicting a large number of physical properties of transition metals. 相似文献
9.
We revisit the problem of a two-dimensional polymer ring subject to an inflating pressure differential. The ring is modeled
as a freely jointed closed chain of N monomers. Using a Flory argument, mean-field calculation and Monte Carlo simulations, we show that at a critical pressure,
pc ∼ N-1, the ring undergoes a second-order phase transition from a crumpled, random-walk state, where its mean area scales as 〈A〉 ∼ N, to a smooth state with 〈A〉 ∼ N2. The transition belongs to the mean-field universality class. At the critical point a new state of polymer statistics is
found, in which 〈A〉 ∼ N3/2. For p ≫ pc we use a transfer-matrix calculation to derive exact expressions for the properties of the smooth state. 相似文献
10.
Jun Song Hong-Yi Fan Ye-Jun Xu Jun Zhou 《International Journal of Theoretical Physics》2011,50(6):1946-1952
By employing the technique of an integral within an ordered product (IWOP) of operators we recast the complex wavelet transform
to a matrix element of the two-mode squeezing-displacing operator U
2(μ,σ) between the mother wavelet vector 〈ψ| and the two-mode quantum state vector |f〉 to be transformed, i.e., we propose that 〈ψ|U
2(μ,σ)|f〉 can be considered as a new kind of spectra for analyzing |f〉, this may have some potential applications in quantum information and calculation. As an example, we numerically calculate
wavelet-transform spectrum for the Bell states, which may play a role of distinguishing them one from another. 相似文献
11.
Theoretical expressions for the local values of six types of unnormalized R-indices are derived for an imperfectly related incomplete model of a crystal (centrosymmetric and non-centrosymmetric) with
truncated data which is characterized by a truncation limit y
t. These indices depend on the parameters σ
1, D and y
t. In the situations of practical interest (i.e., σ
1
2
>0·3 and y
t<0·2) R-indices for the centro-symmetric case decrease as y
tincreases while these for the non-centro-symmetric case remain more or less constant.
Contribution No. 569 相似文献
12.
D. E. Feldman 《JETP Letters》1999,70(2):135-140
The random field and random anisotropy N-vector models are studied with the functional renormalization group in 4−ε dimensions. The random anisotropy Heisenberg (N=3) model has a phase with an infinite correlation length at low temperatures and weak disorder. The correlation function
of the magnetization obeys a power law 〈m(r
1)m(r
2)〉∼|r
1−r
2|− 0.62ε. The magnetic susceptibility diverges at low fields as χ∼H
−1+0.15ε. In the random field N-vector model the correlation length is finite at arbitrarily weak disorder for any N>3.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 2, 130–135 (25 July 1999)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
13.
In this paper certain correspondences have been shown among various formulations of coupled-cluster theories for many electron
closed-shell systems. Specifically it is shown that (i) the energy functional using unitary ansatz of the form exp (T−T
+) is exactly sameorder by order inT with the size-consistent energy functional 〈ψ|H|ψ〉/〈ψ|ψ〉 recently obtained by us in coupled-cluster framework; (ii) in the framework of unitary ansatz of the form exp (T−T
+), both non-variational and variational approaches lead to identical equations upto any given order inT andT
+ inT∼T
2 approximation; (iii) variational procedure using our size-consistent energy functional or using the functional obtained in
the framework of unitary ansatz (as envisaged by Kutzelnigg) leads to energy in both cases, inT∼T
2 approximation, for a total of quadratic powers inT andT
+, same as Cizek’s linearised coupled pair many electron theory energy; (iv) in case of practical calculation of the energy
through the variational procedures using our size-consistent energy functional and the functional in unitary ansatz framework,
there is a loss of upper bound. 相似文献
14.
The statistics of energy levels for a disordered conductor are considered in the critical energy window near the mobility
edge. It is shown that, if the critical wave functions are multifractal, the one-dimensional gas of levels on the energy axis
is compressible, in the sense that the variance of the level number in an interval is 〈 (δN)2〉∼χ〈N〉 for 〈N〉≫1. The compressibility, χ=η/2d, is given exactly in terms of the multifractal exponent η =d−D
2 at the mobility edge in a d-dimensional system.
Pis’ma Zh. éksp. Teor. Fiz. 64, No. 5, 355–360 (10 September 1996)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
15.
The wave mechanics of two impenetrable hard core particles in a 1-D box is analyzed. Each particle in the box behaves like
an independent entity represented by a macro-orbital (a kind of pair waveform). While the expectation value of their interaction, 〈 V
HC
(x) 〉, vanishes for every state of two particles, the expectation value of their relative separation, 〈 x 〉, satisfies 〈 x 〉≥λ/2 (or q ≥ π/d, with 2d=L being the size of the box). The particles in their ground state define a close-packed arrangement of their wave packets (with
〈 x 〉= λ/2, phase position separation Δϕ = 2π and momentum |q
o| = π/d) and experience a mutual repulsive force (zero point repulsion) f
o
=h
2/2md
3 which also tries to expand the box. While the relative dynamics of two particles in their excited states represents usual
collisional motion, the same in their ground state becomes collisionless. These results have great significance in determining
a correct microscopic understanding of widely different many-body systems. 相似文献
16.
The momenta and rapidity characteristics of the particles produced in 50 GeV/c
π
−-collision with emulsion nuclei have been studied with an emulsion stack exposed under a pulsed magnetic field. The longitudinal
rapidity plots suggest that leading pion is attenuated strongly when passing through a heavy nucleus. The average net charge
〈N
s
+
−N
s
−
〉 produced in the final state of the reaction rises rapidly from a negative to a positive value atN
h
⩽1 and attains a constant value⋍0.60±0.08 at allN
h
⩾7. 相似文献
17.
The mean area of a two-dimensional Gaussian ring of N monomers is known to diverge when the ring is subject to a critical pressure differential, p
c ∼ N
-1. In a recent publication (Eur. Phys. J. E 19, 461 (2006)) we have shown that for an inextensible freely jointed ring this divergence turns into a second-order transition
from a crumpled state, where the mean area scales as 〈A〉 ∼ N, to a smooth state with 〈A〉 ∼ N
2. In the current work we extend these two models to the case where the swelling of the ring is caused by trapped ideal-gas
particles. The Gaussian model is solved exactly, and the freely jointed one is treated using a Flory argument, mean-field
theory, and Monte Carlo simulations. For a fixed number Q of trapped particles the criticality disappears in both models through an unusual mechanism, arising from the absence of
an area constraint. In the Gaussian case the ring swells to such a mean area, 〈A〉 ∼ NQ, that the pressure exerted by the particles is at p
c for any Q. In the freely jointed model the mean area is such that the particle pressure is always higher than p
c, and 〈A〉 consequently follows a single scaling law, 〈A〉 ∼ N
2
f (Q/N), for any Q. By contrast, when the particles are in contact with a reservoir of fixed chemical potential, the criticality is retained.
Thus, the two ensembles are manifestly inequivalent in these systems.
An erratum to this article is available at . 相似文献
18.
Using the general formulation for obtaining chemical potentialμ of an ideal Fermi gas of particles at temperature T, with particle rest mass m0 and average density 〈N〉/V, the dependence of the mean square number fluctuation 〈ΔN
2〉/V on the particle mass m0 has been calculated explicitly. The numerical calculations are exact in all cases whether rest mass energym
0c2 is very large (non-relativistic case), very small (ultra-relativistic case) or of the same order as the thermal energy kBT. Application of our results to the detection of the universal very low energy cosmic neutrino background (CNB), from any
of the three species of neutrinos, shows that it is possible to estimate the neutrino mass of these species if from approximate
experimental measurements of their momentum distribution one can extract, someday, not only the density 〈N
v〉/V but also the mean square fluctuation 〈Δ
v
2
〉/V. If at the present epoch, the universe is expanding much faster than thermalization rate for CNB, it is shown that our analysis
leads to a scaled neutrino massm
v
instead of the actual massm
0v
. 相似文献
19.
Néstor Armesto Carlos Pajares Paloma Quiroga-Arias 《The European Physical Journal C - Particles and Fields》2009,62(1):151-157
We study the medium dependence of the multiplicity distributions in the modified leading logarithmic approximation. We focus
in the enhancement in the number of branchings as the partons travel trough a dense medium created in a heavy-ion collision.
We study the effect of a higher number of splittings in some jet observables by introducing the medium as a constant (f
med) in the splitting functions. Having as our ansatz for the quark and gluon jets mean multiplicities 〈n
G
〉=e
γ
y
and 〈n
Q
〉=r
−1e
γ
y
, we study in an analytic approach the dependence with the medium (f
med) of the anomalous dimension (γ), the multiplicity ratio (r), and so the mean multiplicities. We also obtain the higher-order moments of the multiplicity distribution, what allows us
to study its dispersion. 相似文献
20.
Néstor Armesto Carlos Pajares Paloma Quiroga-Arias 《The European Physical Journal C - Particles and Fields》2009,61(4):779-784
We study the modification of the multiplicity distributions in MLLA due to the presence of a QCD medium. The medium is introduced
through a multiplicative constant (f
med) in the soft infrared parts of the kernels of the QCD evolution equations. Using the asymptotic ansatz for mean multiplicities
of the quark and gluons, 〈n
G〉=e
γ
y
and 〈n
Q〉=r
−1e
γ
y
, respectively, we study two cases: fixed γ as previously considered in the literature, and fixed α
s
. We find opposite behaviors of the dispersion of the multiplicity distributions with increasing f
med in both cases. For fixed γ the dispersion decreases, while for fixed α
s
it increases. 相似文献