共查询到20条相似文献,搜索用时 31 毫秒
1.
N. M. Olekhnovich A. V. Pushkarev Yu. V. Radyush 《Journal of Applied Spectroscopy》2009,76(4):518-522
A technique for analysis of the electric modulus spectrum of dielectric ceramics based on the elimination of the direct current
conductivity (σ
dc
) contribution has been developed. Expressions are given for the real (M′
ac
) and imaginary (M′′
ac
) parts of the complex electrical modulus related only to the dielectric polarization and not containing the contribution
of σ
dc
. The frequency dependence of M′′
ac
and the M′′
ac
– M′
ac
diagram for BiMg1/2Ti1/2O3 and BiMg1/2Zr1/2O3 perovskite ceramics are analyzed. 相似文献
2.
M. V. Gorev E. V. Bogdanov I. N. Flerov A. G. Kocharova N. M. Laptash 《Physics of the Solid State》2010,52(1):167-175
The thermal expansion along the principal crystallographic axes of the (NH4)2WO2F4 and (NH4)2MoO2F4 oxyfluorides has been studied. The anomalous behavior of α
i
(T) due to the phase transitions has been revealed at T
1 = 271.4 K and T
2 ≈ 180 K for the molybdate and at T
1 = 201.5 K and T
2 ≈ 161 K for the tungstate. The quantities dT/dp and dT/dσ
i
, which characterize the dependence of the phase transition temperatures on the hydrostatic and uniaxial pressures, have been
determined from analyzing the results of studies of the thermal expansion and heat capacity with the use of the Pippard relations.
The p-T and α
i
-T phase diagrams reflect different characters of the influence of the pressure on the stability of the initial and distorted
phases of the oxyfluorides. The magnitudes of the extensive and intensive barocaloric effects determined in the vicinity of
the structural phase transitions are as follows: ΔS
BCE varies from approximately −10 to −17 J/mol K and ΔT
AD ≈ 8−17 K for the molybdate and ΔS
BCE varies from approximately −10 to −17 J/mol K and ΔT
AD ≈ 8−13 K for the tungstate. 相似文献
3.
P. A. Loiko K. V. Yumashev N. V. Kuleshov A. A. Pavlyuk 《Applied physics. B, Lasers and optics》2012,106(3):663-668
The thermo-optic coefficients, dn/dT, were determined for pure and Yb(20 at.%)-doped monoclinic KY(WO4)2 crystals for light polarized along the optical indicatrix axes (N
p,N
m and N
g) in the wavelength range of 0.36–1.06 μm by a laser beam deviation method. The absolute values of thermo-optic coefficients
satisfy the relation |dn
p/dT|>|dn
g/dT|>|dn
m/dT| and increase with the wavelength increasing. In the long-wavelength range, all the dn/dT values are negative: dn
p/dT=−14.6, dn
m/dT=−8.9, dn
g/dT=−12.4 [10−6 K−1] for pure KY(WO4)2 at 1.06 μm. The dependency of thermo-optic coefficients on the wavelength was modeled using an approach that takes into account
contribution of volumetric thermal expansion and change of electronic bandgap with temperature. Large volumetric expansion
of KY(WO4)2 plays a key role in the observed negative dn/dT values. Electronic bandgap and its temperature coefficient were determined for KY(WO4)2 crystals from thermo-optic dispersion curves as E
g=4.8–5.0 eV and −dE
g/dT=0.7–1.1×10−4 eV/K. Athermal propagation directions were calculated for KY(WO4)2 crystals at the wavelength of 1.06 μm for light polarizations E∥N
m and N
p. 相似文献
4.
P. Contucci M. Degli Esposti C. Giardinà S. Graffi 《Communications in Mathematical Physics》2003,236(1):55-63
Let {E Σ (N)} ΣΣN be a family of |Σ N |=2 N centered unit Gaussian random variables defined by the covariance matrix C N of elements c N (Σ,τ):=Av(E Σ (N)E τ (N)) and the corresponding random Hamiltonian. Then the quenched thermodynamical limit exists if, for every decomposition N=N 1 +N 2 , and all pairs (Σ,τ)Σ N ×Σ N :
where π k (Σ),k=1,2 are the projections of ΣΣ N into Σ Nk . The condition is explicitly verified for the Sherrington-Kirkpatrick, the even p-spin, the Derrida REM and the Derrida-Gardner GREM models. 相似文献
5.
M. Zwilling P. C. Schmidt Alarich Weiss 《Applied Physics A: Materials Science & Processing》1978,16(3):255-269
X-ray and neutron diffraction experiments and optical studies were done on several alloys of the quasibinary series Li2Ag2−x
In
x
, Li2Cd2−x
In
x
, and Li2Zn2−x
Cd
x
. Within a wide region the alloys crystallize homogenous in an NaTl-type structure (1≦x≦1.5 for Li2Ag2−x
In
x
; 0.6≦x≦1 for Li2Cd2−x
In
x
; 1.2≦x≦1.6 for Li2Zn2−x
Cd
x
). Most of the alloys investigated are colored and the color changes continuously as a function ofx. Measurements of the reflectivityr and the dielectric constants (ɛ1 and ɛ2) were done in the energy range 1.5 eV≦E≦3.3 eV by the method of elliptical analysis. In this energy range the curvesr(E) have minima which shift with increasingx to lower energy values. Calculations of the energy bands of LiAg, LiIn, LiCd, and Li2AgIn on the basis of the augmented plane wave method and the determination of the joint density show that the optical data
can be interpretated on the assumption of interband transitions between the valence and the conduction bands and of transitions
between the 4d-bands of silver and the energy states at the Fermi level. 相似文献
6.
Munetaka Takeuchi Yasuo Kameda Yasuhiro Umebayashi Sari Ogawa Takaaki Sonoda Shin-ichi Ishiguro Miho Fujita Mitsuru Sano 《Journal of Molecular Liquids》2009,148(2-3):99-108
Self-diffusion coefficients of Li+ DLi+, PF6− DPF6− and solvent propylene carbonate (PC) DPC in LiPF6−PC solutions were determined at 298 K by the pulse gradient spin echo (PGSE) NMR technique over the salt concentration range of 0.1–3.0 M (M = mol dm– 3). The order of the diffusion coefficients was found to be DLi+ < DPF6− < DPC over the concentration range examined, and they were monotonically decreased with increasing the salt concentration. Haven ratio Λ/ΛNMR, where Λ and ΛNMR represent the ionic conductivity measured electrochemically and that estimated via the Nernst-Einstein equation using the diffusion coefficient, respectively, was evaluated as the measure of the ion–ion interaction in the LiPF6–PC solutions. Though Λ/ΛNMR values for LiPF6-solutions decrease with increasing the salt concentration, they were greater than those for LiBF4–PC solutions over the whole concentration range examined, which indicates that the ion pair formation ability of PF6– ion is weaker than that of the BF4– ion. The smaller value of the ionic conductivity for the highly concentrated LiPF6–PC solution (above 2.0 M) than that of the LiBF4-solutions can be attributed to the more rapidly increased viscosity relative to the LiBF4-solution. Classic molecular dynamics (MD) simulations for the respective LiPF6 and LiBF4-solution of 0.5 and 1.0 M were also carried out based on the effective pair potentials. Diffusion coefficients, ionic conductivity and Haven ratio for these solutions were calculated from MD trajectories, and they qualitatively agree with those evaluated by experiments. Pair correlation functions gLiO(r) (for Li+–O (PC) pair) and gLiPF6(r) (for Li+–PF6– pair) or gLiBF4(r) (for Li+–BF4– pair) revealed that the lithium ion weakly forms the contact ion pairs with PF6–, whilst strongly with BF4–, which supports the present experimental results. Moreover, the simulation results show that both anions in the contact ion pairs predominantly take the monodentate form, which is in contrast to the multidentate coordination predicted by ab initio calculation in gas phase. 相似文献
7.
E. L. Korotyaev 《Russian Journal of Mathematical Physics》2011,18(4):427-439
The Jacobi operator (Jf)
n
= a
n−1
f
n−1 +a
n
f
n+1 + b
n
f
n
on ℤ with real finitely supported sequences (a
n
− 1)
n∈ℤ and (b
n
)
n∈ℤ is considered. The inverse problem for two mappings (including their characterization): (a
n
, b
n
, n ∈ ℤ) → {the zeros of the reflection coefficient} and (a
n
, b
n
, n ∈ ℤ) → {the eigenvalues and the resonances} is solved. All Jacobi operators with the same eigenvalues and resonances are
also described. 相似文献
8.
Empirical formula suggested by Kita and Koizumi for evaluation of relaxation intensity in a limited range of frequency around
the relaxation frequency for the Cole-Cole type distribution has been tested for poly butyl acrylate (PBA), Poly butyl methacrylate
(PBMA) and poly isobutyl methacrylate (PiBMA).
The relaxation intensity Δε is expressed in terms ofε″
M
, the dielectric loss maxima andW, the frequency separation for half, two thirds or three quarters ofε″
M
, in the form Δε=ε″
M
/[(C
1/W)+C
2+C
3
W], where the numerical constantsC
1,C
2,C
3 are given for the respective type of relaxation. 相似文献
9.
I.O. Troyanchuk N.V. Tereshko A.N. Chobot M.V. Bushinsky K. Brner 《Physica B: Condensed Matter》2009,404(21):4185-4189
The Bi1−xAxFe1−xTixO3 (A—Ca, Sr, Pb, Ba) and BiFe1−xTixO3+δ systems have been studied using X-ray, neutron powder diffraction and magnetization measurements in a magnetic field up to 14 T. It was found that all Bi1−xAxFe1−xTixO3 solid solutions are rhombohedral up to x=0.3. In the case of BiFe1−xTixO3+δ the rhombohedral distortion preserved up to x=0.11. A homogeneous weakly ferromagnetic state was found for Bi1−xCaxFe1−xTixO3 (0.15≤x≤0.25) and BiFe1−xTixO3+δ (0.06≤x≤0.11), probably due to magnetoelectric interactions, whereas Bi1−xAxFe1−xTixO3 (A—Sr, Pb, Ba) compounds above doping level x>0.1 seem to be collinear antiferromagnets. 相似文献
10.
In the heat-bath Glauber dynamics for the Ising model on the lattice, physicists believe that the spectral gap of the continuous-time
chain exhibits the following behavior. For some critical inverse-temperature β
c
, the inverse-gap is O(1) for β < β
c
, polynomial in the surface area for β = β
c
and exponential in it for β > β
c
. This has been proved for
\mathbbZ2{\mathbb{Z}^2} except at criticality. So far, the only underlying geometry where the critical behavior has been confirmed is the complete
graph. Recently, the dynamics for the Ising model on a regular tree, also known as the Bethe lattice, has been intensively
studied. The facts that the inverse-gap is bounded for β < β
c
and exponential for β > β
c
were established, where β
c
is the critical spin-glass parameter, and the tree-height h plays the role of the surface area.
In this work, we complete the picture for the inverse-gap of the Ising model on the b-ary tree, by showing that it is indeed polynomial in h at criticality. The degree of our polynomial bound does not depend on b, and furthermore, this result holds under any boundary condition. We also obtain analogous bounds for the mixing-time of
the chain. In addition, we study the near critical behavior, and show that for β > β
c
, the inverse-gap and mixing-time are both exp[Θ((β − β
c
)h)]. 相似文献
11.
12.
The emission spectrum of the PSe radical is reported for the first time. Seventy-eight reddegraded bands in the region 4000–6500 Å have been measured and assigned to the A2Π-X2Π transition of PSe. Isotope shifts observed for some bandheads have been utilized in deriving the vibrational numbering. The molecular constants have been determined as (in units of cm−1): ω′ = 406.9, ω′eχ′e = 1.3, ω″ = 556.9, ω″eχ″e = 1.3, and Te = 19477.3 for the 2Π1/2 states; and ω′e = 402.4, ω′eχ′e = 1.5, ω″e = 556.8, ω″eχ″e = 1.6, and Te = 19178.0 for the 2Π3/2 states. 相似文献
13.
Boltzmann-transport equation is analytically solved for two-component magnetoplasma using Chapman-Enskog analysis to include
collisional diffusion transport having anisotropies in both streaming velocity and temperature components. The modified collisional
integrals are analytically solved with flux integrals and perturbed kinetic equation to arrive at drift diffusion velocity
and resulting transport coefficients which are markedly affected by both streaming and temperature anisotropy. The early isotropic
results are recovered in the limit V
0 = 0 and T
‖ = T
⊥ which reduce to eqs (11.30) and (11.31) of [1] and eqs (2.7) and (2.13) of [2]. The electrical resistivity (η⊥) diminishes sharply in fusion temperature limit kT
⊥ = 1 keV. The shape of the curves for both electrical resistivity and thermal conductivity is rectangular hyperbolic. However,
for low thermal ratio (T
‖/T
⊥ < 1), the curves are raised up and for high thermal ratio (T
‖/T
⊥ > 1), they are lowered down the isotropic case (T
‖/T
⊥ > 1), showing comparatively diminished magnitudes of the quantities.
相似文献
14.
Given a countably infinite 0–1 matrix A without identically zero rows, let 𝒪
A
be the Cuntz–Krieger algebra recently introduced by the authors and 𝒯
A
be the Toeplitz extension of 𝒪
A
, once the latter is seen as a Cuntz–Pimsner algebra, as recently shown by Szymański. We study the KMS equilibrium states
of C
*
-dynamical systems based on 𝒪
A
and 𝒯
A
, with dynamics satisfying for the canonical generating partial isometries s
x
and arbitrary real numbers N
x
> 1. The KMSβ states on both 𝒪
A
and 𝒯
A
are completely characterized for certain values of the inverse temperature β, according to the position of β relative to
three critical values, defined to be the abscissa of convergence of certain Dirichlet series associated to A and the N(x). Our results for 𝒪
A
are derived from those for 𝒯
A
by virtue of the former being a covariant quotient of the latter. When the matrix A is finite, these results give theorems of Olesen and Pedersen for 𝒪
n
and of Enomoto, Fujii and Watatani for 𝒪
A
as particular cases.
Received: 21 November 2000 / Accepted: 31 May 2002 Published online: 22 November 2002
RID="*"
ID="*" Partially supported by CNPq
RID="**, ***" 相似文献
15.
The relaxation processes (α, β, and γ) in UHMW PE fibres drawn to different draw ratios λ have been studied by dynamic-mechanical and nuclear magnetic resonance methods. The temperature dependences of tensile loss
moduli E″ and spin-lattice relaxation times T
1 have been analyzed assuming distribution of correlation times τ according to the Davidson—Cole function. The activation energies E
a and parameters ε characterizing widths of distribution, and asymptotic value τ
0 for correlation times have been determined from experimental data for low-temperature γ-process and for high-temperature α-process. A weak β-process has been found by dynamic-mechanical method and quantitative analysis was made only for fibres with λ = 9. The temperature dependences of second moment M
2 of the broad-line NMR spectra have been analyzed according to the Gutowsky—Pake formula, which includes only a single correlation
time τ
c without distribution. In this case the activation energies E
a and values of τ
0 have been determined. 相似文献
16.
The rare t-quark decays t → cl
j
+
l
k
−
and t → cṽ
j
k
k
induced by scalar-leptoquark doublets are considered within the minimal model involving four-color quark-lepton symmetry
and the Higgs mechanism of quark and lepton mass splitting. The partial widths with respect to the decays being considered
and the total widths Γ(t → cl
+′l
−) = Σj,k Γ(t → cl
j
+
l
k
−
) and Γ(t → cl
+′l
−) = Σj,kΓ(t → cṽ
j
v
k
) with respect to, respectively, the charged leptonic and neutrino modes are calculated. It is shown that, at scalar-leptoquark
masses higher than the t-quark mass (m
S > m
t), the branching ratios for these modes are Br(t → cl
+′l
−) ≈ (3.5−0.4) × 10−5 and Br(t → cṽ′v) ≈ (7.1−0.8) × 10−5 at m
s
= 180–250 GeV and an appropriate value of the leptoquark-mixing angle (sin β ≈ 0.2) and can increase for m
S < m
t to Br(t → cl
+′l
−) ≈ 0.03−0.002 and Br(t → cl
+′l
−) ≈ 0.46−0.05 for the charged mode at m
S
= 150–170 GeV for sin β ≈ 1 and sin β ≈ 0.2, respectively. In the cases being considered, t-quark decays to pairs of charged leptons can be accessible to detection at LHC. In the last case, these decays could manifest
themselves (for example, in dilepton events) at the Tevatron as well.
Original Russian Text ? P.Yu. Popov, A.D. Smirnov, 2006, published in Yadernaya Fizika, 2006, Vol. 69, No. 6, pp. 1006–1016. 相似文献
17.
Bi4V2O11 exists in three phases viz. α, β, and γ. High temperature γ-phase can be stabilized to room temperature owing to its higher
conductivity by the partial substitution of metallic cations for vanadium in Bi4V2O11. Phase transitions from α → β and β → γ are composition and temperature-dependent. Mn2+-doped compounds Bi4V2−x
Mn
x
O11−
δ
(0 ≤ x ≤ 0.4) have been synthesized by solid state reaction technique and investigated by X-ray diffraction and ionic conductivity
measurement. High ionic conducting γ-phase is stabilized for x ≥ 0.2. The ionic conductivity of the series of Bi4V2−x
Mn
x
O11−
δ
samples has been measured by using ac impedance spectroscopy technique. The conductivity data do show departure from its
simple Arrhenius behavior for all of the compositions. The highest conductivity observed for x = 0.2 sample can be attributed to lower activation energy. 相似文献
18.
The fundamental properties of the AlN and GaN compounds with a wurtzite structure under external hydrostatic pressure, uniaxial
mechanical stress σ⊥ along the hexagonal axis, and biaxial mechanical stress σ⊥ in the basal plane of the unit cell have been considered in terms of first-principles calculations in the frame-work of the
density functional theory. The pressures of the phase transitions from the structures of wurtzite and zinc blende to the structure
of rock salt have been obtained. The behavior of the structural parameters, interband transitions, and positions of the charge
neutrality level has been investigated. The calculated pressure coefficients of the band gap are as follows: ∂E
g
/∂p = 40.9 meV/GPa, −∂E
g
/∂σ
| = −4.2 meV/GPa, and −∂E
g
/∂σ
⊥ = 45.2 meV/GPa for AlN and ∂E
g
/∂p = 33.0 meV/GPa, −∂E
g
/∂σ
| = 23.6 meV/GPa, and −∂E
g
/∂σ
⊥ = 9.6 meV/GPa for GaN. The pressure coefficients of the charge neutrality level in almost all cases are substantially smaller
than the corresponding values obtained for the band gap E
g
. 相似文献
19.
Piotr Śniady 《Communications in Mathematical Physics》2001,216(3):515-537
We construct a family of random matrix models for the q-deformed Gaussian random variables G
μ=a
μ+a^*μ, where the annihilation operators a
μ and creation operators $a\gwia_\nu$ fulfill the $q$-deformed commutation relation a
μ
a^*ν−q
a^*ν
a
μ=Γμν, Γμν is the covariance and 0<q<1 is a given number. An important feature of the considered random matrices is that the joint distribution of their entries
is Gaussian.
Received: 29 March 2000 / Accepted: 1 August 2000 相似文献
20.
Edward A. Desloge 《International Journal of Theoretical Physics》1976,15(5):357-363
On the basis of elementary symmetry arguments it is shown that (1) if in classical mechanics there exists a quantity λ+Σiμiυi+1/2νυ
2 that is conserved, where λ,μ
i, andν are particle parameters, then theμ
i andν are all proportional to a single parameterμ and the quantityAμ+ΣiBiμυi+C(λ+ 1/2Dμυ
2), whereD ≡ν/μ, is conserved for all values ofA, B
i, andC; (2) if in relativistic mechanics there exists a quantity λ+Σiμiυi[1−(υ
2/c
2)]−1/2+νc[1−(υ
2/c
2)]−1/2 that is conserved, then theμ
i andν are all proportional to a single parameterμ and the quantityAλ+ΣiBiμνi[1−(υ
2/c
2)]−1/2+Cμc [1−(υ
2/c
2)]−1/2 is conserved for all values ofA, B
i, andC. 相似文献