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1.
Abstract An optical autoclave for phase studies on mixtures in the temperature range from 80 to 373 K and for pressures up to 200 MPa is described. The cell is fitted with sapphire windows and employs magnetic stirring. Measurements are performed according to the synthetical (e.g. by visual observation) or analytical method (e.g. by sampling and online gaschromatography). Results for the crystallization and fluid phase equilibria of the binary systems nitrogen + trifluoromethane and argon + trifluoromethane from 110 K to 230 K and up to 200 MPa are presented and discussed in comparison with other N 2- and CHF 3-systems. 相似文献
2.
The purpose of this research is to study the effect of doping Gd into
Pb(Zr 0.52Ti 0.48)O 3 ceramics prepared by solid state reaction.
X-ray diffraction patterns show that all PGZT samples are of tetragonal
structure and the highest doping should be no more than 2 mole % Gd at
which the unreacted oxides start to appear. The electron spin resonance
(ESR) spectra of PGZT's indicate that Gd 3+ can enter both A site of the
perovskite structure instead of only A site as widely believed. The ESR
peaks resonance shift towards low fields as the concentration is higher,
which is due to the change in crystal field experienced by Gd 3+ ions.
At x =0.001, 0.005 and 0.01 dopings, two sets of powder ESR signals arising
from Gd 3+ (4f 7, spin 7/2) ions at A site. The first set shows some
fine structure having strong absorption peaks centered at 76.26 mT (g =
8.550). The second is a seven-peak spectrum centered at 206.01 mT (g =
3.165), which belongs to the Gd 3+ ions at B sites. Furthermore, the
overlapped ESR strong absorption peaks from 309.17 mT to 314.49 mT (g =
2.2818-2.1087) belong to Gd 3+ of unreacted Gd 2O 3. The local
environments of Gd 3+ ions were verified from the calculated ESR spectra
using appropriate spin Hamiltonian parameter, i.e. gyromagnetic tensor
g, zero-field splitting D and hyperfine tensor
A. 相似文献
3.
Abstract When tracing the fluxes of N compounds (especially N oxides) and carbon dioxide in the system soil-atmosphere and applying 15N and 13C, it is necessary to simultaneously determine both the concentration of the substances and their isotopic composition. GC separation (packed column) was coupled to a mass spectrometer by a special interface. Variable sample volumes can be delivered by changing the split by means of the interface in front of the MS. Thus, both the concentration of a gaseous compound and its 15N content can be measured. Supplying sample volumes in a range between 5 μl and 5 ml, it is possible to measure both components of high content (e.g., nitrogen) and at the lower ppm(v)-content (e.g., dinitrogen oxide) in the air. Measurements of N 2, N 2O, NO and CO 2 are demonstrated, too. 相似文献
4.
The purpose of this paper is to review and to extend, wherever possible, the Kramers-Kronig relations, sum rules, and symmetry properties for the electrodynamic transport tensors of a linear plasma medium. For complete generality, we consider both nonrelativistic and relativistic plasmas with and without external magnetic fields. Our study is carried out first within the framework of classical electrodynamics. We then exploit the statistical-mechanical fluctuation-dissipation theorem to further obtain the Onsager symmetry relations and Kubo sum-rule frequency moments. Of special significance is the emergence of a variety of new Kramers-Kronig formulae and f-sum rules for the inverse dispersion tensor.Nomenclature
E(k, )
electric field intensity
-
Ê(k, )
electric field in absence of plasma particles,
-
( k, )
electric field due to the plasma particles (= E- Ê)
-
B(k, )
magnetic induction
-
D(k, )
electric induction
-
H(k, )
magnetic field strength
-
B
0
constant external magnetic field
-
A
0
vector potential corresponding to B
0
-
( k, ), j( k, co)
charge and current densities due to the plasma particles
-
( k, ), J( k, )
charge and current densities of the external agency
- ( k, , B
0)
dielectric tensor of the plasma medium in the presence of B 0
- ( k, , B
0)
diamagnetic tensor
-
( k, co, B
0)
( k, , B
0) – 1, electric polarizability tensor
- ( k, , B
0)
magnetic polarizability tensor
- ( k, , B
0)
ordinary conductivity tensor
-
( k, , B
0)
external conductivity tensor
- D( k, , B
0)
n 2T–( k, , B
0), dispersion tensor, where T=1- kk is the transverse projection tensor ( k being the unit vector in the direction of k) and n = kc/ the index of refraction
-
n 2T – 1, = vacuum wave operator (value of D in vacuum)
-
1/2( +
), Hermitian part of
- ^
1/2( – ), Anti-Hermitian part of a
- ,
real and imaginary parts of a
- R( r, t)
dissipated power per unit volume of plasma
-
U
total energy absorbed by the plasma
- R( k, )
E *( k, ) · ( k, , b
0) · E( k, ) corresponding spectral energy density
- W( r, t)
1/2 0E 2(r, 0 + (l/2 0) B 2( r, t), field energy density
- W( k, )
1/2 0E *k, ) · E( k, ) + (l/2 0) B
*( k, ) · B( k, ), energy content in a certain domain of ( k, )-space for a single mode
-
x
i, p
i, v
i
coordinate, momentum, and velocity of ith electron
-
i
[1–( i
2/c 2)] –1/2
-
X
j, P
j, V
j
coordinate, momentum, and velocity of jth ion
- { A
q}, {E q}
field coordinates and momenta
- j k( t), J
k( t)
perturbations in the microscopic electron and ion current densities due to the presence of the small external vector potential agency â( r, t) = (1/L 3) â k( t) exp i
k · r
-
Liouville distribution function = 0 +
- 0
macrocanonical distribution function characterizing the equilibrium state of the system in the infinite past
-
small perturbation due to A
- H 0
Hamiltonian of equilibrium system which includes interaction
-
H
Hamiltonian for the interaction between the system and the small external perturbing agency A
- 0 = d R() 0
expectation value of any quantity over the equilibrium ensemble (d R is an element of hypervolume in -phase space)
- G(12)
two-particle distribution function
- F(1)
one-particle distribution function
- g(¦x 2 – x 1 ¦)
[G(12)/F(1)F(2)] – 1, pair correlation function
-
N
total number of electron in volume L 3
-
n
0
equilibrium density (of electrons)
-
–1
temperature (in energy units)
- 0
(n 0e 2/m 0) 1/2, equilibrium electron plasma frequency
- c
¦ e ¦– B
0/m, electron frequency
-
–1
(
0/n 0e 2) 1/2, Debye length
-
0
(n 0Ze 2/M 0) 1/2, equilibrium ion plasma frequency
-
c
ZeB 0/M, ion cyclotron frequency 相似文献
5.
ABSTRACT The optical spectra and electron spin resonance (ESR) g factor of Ni 2+-doped sodium phosphate glasses are uniformly studied on the basis of both the complete (energy matrix) diagonalization procedure (CDP) and the two spin-orbit coupling parameters model. The bond length of Ni 2+-O 2? of Ni 2+-doped sodium phosphate (Na 2O · P 2O 5) glasses has been determined by fitting their optical spectra and ESR g factor to the experimental values. Theoretical results are in good agreement with experimental data. 相似文献
6.
Abstract The dynamics of C and N in terrestrial ecosystems are not completely understood and the use of stable isotopes may be useful to gain further insight in the pathways of CO 2 emissions and leaching of dissolved organic carbon (DOC) and nitrogen (DON) during decomposition of litter. Objectives were (i) to study the decomposition dynamics of Calamagrostis epigeios, a common grass species in forests, using 13C-depleted and 15N-enriched plants and (ii) to quantify the effect wood ash addition on the decomposition and leaching of DOC and DON. Decomposition was studied for 128 days under aerobic conditions at 8°C and moisture close to field capacity in a spodic dystric Cambisol with mor-moder layer. Variants included control plots and additions of (i) Calamagrostis litter and (ii) Calamagrostis litter plus 4 kg ash m ?2. -
Decomposition of Calamagrostis resulted in a CO2 production of 76.2 g CO2–C m?2 (10% of added C) after 128 days and cumulative DOC production was 14.0 g C m?2 out of which 0.9g C m?2 was Calamagrostis-derived (0.1% of added C). The specific CO2 formation and specific DOC production from Calamagrostis were 6 times higher (CO2) and 4 times smaller (DOC) than those from the organic layer. The amount of Calamagrostis-derived total N (NH4 +, NO3 ?, DON) leached was 0.7g N m?2 (4.8% of added N). Cumulative DON production was 0.8g N m?2 which was slightly higher than for the control. During soil passage, much of the DOC and DON was removed due to sorption or decomposition. DOC and DON releases from the mineral soil (17cm depth) were 6.3g C m?2 and 0.5g N m?2. Addition of ash resulted in a complete fixing of CO2 for 40 days due to carbonatisation. Afterwards, the CO2 production rates were similar to the variant without ash addition. Production of DOC (98.6g C m?2) and DON (2.5g N m?2) was marked, mainly owing to humus decay. However, Calamagrostis-derived DOC and Culamagrostis-derived total N were only 3.9g C m?2 (0.5 YO of added C) and 0.5g N m?2 (3.4% of added N). The specific DOC production rate from the organic layer was 6 times higher than that from Cularnagrostis. The results suggest that with increasing humification from fresh plant residues to more decomposed material (OF and OH layers) the production ratio of DOC/CO2-C increases. Addition of alkaline substances to the forest floor can lead to a manifold increase in DOC production. 相似文献
7.
Abstract The volume of activation found for the [4+2]-Diels-Alder cyclodimerization of 1,3-butadiene leading to 4-vinylcyclohexene turned out to be substantially lower than that found for the competing [2+2]-cyclodimerization leading to trans-divinylcyclobutane (ΔΔ 0 #= ?12cm 3mol ?1). The [4+2]-cyclodimerization of Z, Z-1,4-dideuterio-l,3-butadiene shows only 3 % loss of stereochemistry at 1 bar and <1 % at 6.8–8.0 kbar. These findings show good evidence for a stereospecific pericylic Diels-Alder mechanism competing with a small amount of nonstereospecific stepwise reaction which is almost completely suppressed at high pressure. The volumes of activation and reaction for the various dimerization pathways of 1,3-butadiene are calculated by a Monte-Carlo computer simulation. The good agreeement between experimental and simulated data confirms the hypothesis that configurational effects (e.g. different packing of cyclic and acyclic states) are important for the explanation of activation and reaction volumes. 相似文献
8.
A model for the spin-spin relaxation of glassy paramagnetic substances in external magnetic fields is developed and applied to frozen aqueous solutions of Fe(NO 3) 3. In these the ferric ions are surrounded by weakly distorted octahedral complexes of water molecules. The relaxation process is characterized by several relaxation frequencies which replace the single flip frequency of earlier approaches. In contrast to the latter, they can be calculated from the microscopic properties of the sample. The only model parameter is the ligand field coupling constant D determining the relaxational behavior. A set of Mössbauer spectra, measured under various experimental conditions, is well described by a single value of the ligand field parameter D = 2.2g B kG. Some characteristic features of the model become obvious in the spectra, e.g. the fading of certain absorption lines with increasing Fe 3+ concentration. 相似文献
10.
Abstract A 53-atomic model of T d symmetry was assumed for the PMo 12O 40 3? ion. It was succeeded to perform a complete vibrational analysis for this structure. The main force constants are reported along with the complete sets of spectroscopically active frequencies, viz.: 9A 1 (Ra) + 13E (Ra) + 22F 2(ir+Ra). The calculated values are tentatively correlated with infrared data from literature and so far unpublished Raman data. 相似文献
11.
Abstract The limitations of quantifying organic carbon (OC) or various organic substances in sediment from the integration of infrared C–H stretching bands using diffuse reflectance infrared Fourier transform (DRIFT) spectra are pointed out, both from theoretical arguments and by presenting experimental data. Such determinations are inaccurate and imprecise because (i) the band at 2930 cm ?1 is not exclusively due to CH 2 groups; (ii) there is a spectral interference from CO 3 2? absorption; and (iii) the proportion of CH 2 groups in organic matter varies for different sediments. The measurement of aliphatic C–H stretching band areas only provides an approximate measurement of aliphatic carbon bonded to hydrogen, which turns out to be a factor of about 3 to 3.5 times smaller than the OC content for Hong Kong marine sediments, depending on their nature and origin. 相似文献
12.
We present detailed data and analysis of the effects of Zn substitution on the planar Cu site in YBa 2Cu 3O 6+x (YBCO 6+x) as evidenced from our 89Y NMR measurements on oriented powders. For x << 1x \ll 1 we find additional NMR lines which are associated with the Zn substitution. From our data on the intensities and temperature dependence of the shift, width, and spin-lattice relaxation rate of these resonances, we conclude that the spinless Zn 3 d 10 state induces local moments on the near-neighbour (nn) Cu atoms. Additionally, we conjecture that the local moments actually extend to the farther Cu atoms with the magnetization alternating in sign at subsequent nn sites. We show that this analysis is compatible with ESR data taken on dilute Gd doped (on the Y site) and on neutron scattering data reported recently on Zn substituted YBCO 6 + x. For optimally doped compounds 89Y nn resonances are not detected, but a large T-dependent contribution to the 89Y NMR linewidth is evidenced and is also attributed to the occurence of a weak induced local moment near the Zn. These results are compatible with macroscopic magnetic measurements performed on YBCO 6 + x samples prepared specifically in order to minimize the content of impurity phases. We find significant differences between the present results on the underdoped YBCO 6 + x samples and 27Al NMR data taken on Al 3+ substituted on the Cu site in optimally doped La 2CuO 4. Further experimental work is needed to clarify the detailed evolution of the impurity induced magnetism with hole content in the cuprates. 相似文献
14.
The material-specific electronic band structure of the electron-doped high- T
c cuprate Nd 1.85Ce 0.15CuO 4 (NCCO) is calculated in the pseudogap regime using the recently developed generalized LDA + DMFT + Σ
k
scheme. The LDA/DFT (density-functional theory within local density approximation) provides model parameters (hopping integral
values and local Coulomb interaction strength) for the one-band Hubbard model, which is solved by the DMFT (dynamical mean-field
theory). To take pseudogap fluctuations into account, the LDA + DMFT is supplied with an “external” k-dependent self-energy Σ
k
that describes interaction of correlated conducting electrons with nonlocal Heisenberg-like antiferromagnetic (AFM) spin
fluctuations responsible for the pseudogap formation. Within this LDA + DMFT + Σ
k
approach, we demonstrate the formation of pronounced hot spots on the Fermi surface (FS) map in NCCO, opposite to our recent
calculations for Bi 2Sr 2CaCu 2O 8 − δ (Bi2212), which have produced a rather extended region of the FS “destruction.” There are several physical reasons for this
fact: (i) the hot spots in NCCO are located closer to the Brillouin zone center; (ii) the correlation length ξ of AFM fluctuations
is longer for NCCO; (iii) the pseudogap potential Δ is stronger than in Bi2212. Comparison of our theoretical data with recent
bulk-sensitive high-energy angle-resolved photoemission (ARPES) data for NCCO provides good semiquantitative agreement. Based
on that comparison, an alternative explanation of the van Hove singularity at −0.3 eV is proposed. Optical conductivity for
both Bi2212 and NCCO is also calculated within the LDA + DMFT + Δ
k
scheme and is compared with experimental results, demonstrating satisfactory agreement.
The text was submitted by the authors in English. 相似文献
15.
The glass systems xCuO
.
(1 -
x)TeO 2 and xCuO
.
(1 -
x)[75TeO 2
.
25B 2O 3] with 0 <
x
? 50 mol% were investigated by means of X-ray diffraction, electron paramagnetic resonance (EPR) and a.c. magnetic susceptibility
(
) measurements, the principal aim of the investigation being the study of the structural modifications in the tellurite glasses
introduced by the addition of boron oxide. In the case of first glass system, i.e. without B 2O 3, EPR spectra of Cu 2+ ions undergo changes with the increasing concentration of CuO. At very low concentrations, spectra are due to isolated Cu 2+ ions in axially distorted octahedral sites. The EPR signal for samples with 3 ?
x
? 20 mol% can be explained as being the superposition of two EPR absorptions, one showing the hyperfine structure typical for
isolated Cu 2+ ions and the other consisting of a symmetric line typical for clustered ions. The broadening of the absorption band is due
to dipolar as well exchange interaction. The susceptibility data show that for x
> 20 mol%, the Cu 2+ ions are predominantly clustered and are coupled through antiferromagnetic exchange interaction. A comparative study of amorphous
X-ray diffraction pattern of the glasses indicates a structural modification in the TeO 2 network with increasing CuO concentration; the effect is quite visible in the samples with CuO concentrations higher than
20 mole percent. Measurements of density corroborate the conclusions drawn from the X-ray diffraction. Additionally, we show
that our data validates a model in which CuO rich regions are surrounded by a buffer boundary which separates them from the
tellurite glassy network; effect of introducing B 2O 3 can be best described as breaking these regions into smaller size regions.
Received 23 October 2000 and Received in final form 1st February 2001 相似文献
16.
This article examines results of x-ray emission spectroscopy and x-ray diffractometry of amorphous and crystalline layers of certain germanides of iron-group transition metals. Combined analysis of the K- and L-bands of Me and Ge in Me 2 (Fe, Co, Ni)Ge and data from model interpretation of radial distribution functions of atoms in amorphous layers are used to make conclusions on the character of the chemical bond and the structure of the short-range order in the materials studied. It was established that there is no significant change in the character of the chemical bond in germanides Me 2(Fe, Co, Ni)Ge in the transition from the crystalline to the amorphous state. It was also found that short-range order in the investigated amorphous layers can be described by a complex poly-structural atom distribution, i.e. it is characterized by a complex, microscopically nonuniform model of the type Me 2Ge+Me.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 39–43, January, 1986. 相似文献
17.
The oxygen deficient cobaltites LnBaCo 2O 5 (Ln = Tb, Dy, Ho) exhibit two successive crystallographic transitions at T
N
∼340 K and at T
CO
∼210 K. Whereas the first transition (P4/mmm to Pmmm) is related to the long-range antiferromagnetic ordering of the Co ions
(spin ordering), the second transition (Pmmm to Pmmb) corresponds to the long-range ordering of the Co 2+ and Co 3+ species (charge ordering) occurring in 1:1 ratio in the structure. The charge ordered (CO) state was directly evidenced by
the observation of additional superstructure peaks using neutron and electron diffraction techniques. The CO state was also
confirmed indirectly from refinement of high resolution neutron diffraction data as well as from resistivity and DSC measurements.
From the refined saturated magnetic moment values only, ∼3.7
and ∼2.7
, the electronic configuration of the Co ions in LnBaCo 2O 5 remains conjectural. Two pictures, with Co 3+ ions either in intermediate spin state ( t
5
2g
e
1
g
) or in high spin state ( t
4
2g
e
2
g
), describe equally well our experimental data. In both cases, the observed magnetic structure can be explained using the
qualitative Goodenough-Kanamori rules for superexchange. Finally, in contrast to the parent Ln = Y compound [Vogt et al. , Phys. Rev. Lett. 84, 2969 (2000)], we do not report any spin transition in LnBaCo 2O 5 (Ln = Tb, Dy, Ho).
Received 13 December 2000 相似文献
18.
Firstly, imaginary frequency-dependent dipole polarizabilities of Li in its
2
S ground state and the first
2
P excited state are calculated from a time-dependent gauge-invariant method using effective core pseudo-potentials and the
multi-configuration one-electron wave function. C 6 dispersion coefficients of the 2
s
+ 2
s and 2
s
+ 2
p dissociations are deduced and also compared with all-electron values. Then, static polarizabilities of Li 2 in its ground and first excited
1, 3
Σ
+
g,u
states are obtained at interatomic distance corresponding to the energy minimum of each state.
Received 10 May 2001 and Received in final form 14 September 2001 相似文献
19.
In this paper, we prove the following improved Vitali–Hahn–Saks measure convergence theorem: Let (L, 0, 1) be a Boolean algebra with the sequential completeness property, (G, ) be an Abelian topological group, be a nonnegative finitely additive measure defined on L, { n: n N} be a sequence of finitely additive s-bounded G-valued measures defined on L, too. If for each a L, { n(a)} n N
is a -convergent sequence, for each n N, when { (a )} convergent to 0, { n(a )} is -convergent, then when { (a )} convergent to 0, { n(a )} are -convergent uniformly with respect to n N 相似文献
20.
Within the RPA approach for T=0, the excitations of the Heisenberg spin glass system Eu
x
Sr 1–x
S are studied by numerical methods, using a continued fraction algorithm. Both the density of states g(E) and also the spectral function S( q, E) are calculated for systems with (16) 3 sites, with x=0.4, 0.5, and 0.6 (spin glass phase), and also for x0.7 (ferromagnetic phase). For q-vectors within the (1,1,1) plane, S( q, E) shows magnon peaks even in the spin glass phase, over the whole range of q. However, these peaks are quite broad, and there is considerable intensity at small energies even for large q, leading to a finite intercept of g(E) for E0. Over a large temperature range, the specific heat is approximately linear in T for x0.7. 相似文献
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