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2.
The investigation of the specific heat of a RbDy(WO 4) 2 single crystal at temperatures 0.2–2.5 K and in magnetic fields up to 2 T are reported. The temperature dependence of the
specific heat near T
N=0.818 K is compared with the predictions for different models. The 2 D Ising model describes satisfactorily C( T) below T
N, while for T> T
N none of the theoretical models agree with the behavior of C( T) of RbDy(WO 4) 2. The H- T phase diagram for H∥ c is complicated and possesses a triple point, where regions of existence of three magnetic phases converge. The magnetic ordering
is analyzed from the standpoint of the Jahn-Teller nature of the structural phase transitions occurring in RbDy(WO 4) 2 at higher temperatures. It is shown that the form of the phase diagram depends on the direction of the vector H, for the general case of an arbitrary direction of H, two phase transitions can occur with increasing field.
Fiz. Tverd. Tela (St. Petersburg) 41, 491–496 (March 1999) 相似文献
3.
The goal of this paper is to show somewhat unexpected globally pathologic properties in universes described by a class of static planary symmetric exact solutions with G
6-group of motion. In order to achieve this aim, the Killing vectors, the null geodesics and the Penrose diagrams corresponding to different expressions of g
44=– e
2f(z), with f( z) solutions of Einstein's equations, have been employed. Finally, woking in a particular gauge, we focus on the behaviour of the radiating electromagnetic modes and derive the observable components of E and B and the expressions of the essential component of the Umov-Poynting vector. 相似文献
4.
Single crystals of [( R)-C 5H 14N 2][Cu(SO 4) 2(H 2O) 4]·2H 2O ( 1) were grown through the slow evaporation of a solution containing H 2SO 4, ( R)-C 5H 12N 2 and CuSO 4·5H 2O. These crystals spontaneously transform to [( R)-C 5H 14N 2] 2[Cu(H 2O) 6](SO 4) 3 ( 2) over the course of four days at room temperature. The same single crystal on the same mounting was used for the determination of the structure of ( 1) and the unit cell determination of ( 2). A second single crystal of the transformed batch has served for the structural determination of ( 2). Compound 1 crystallizes in the noncentrosymmetric space group P2 1 (No. 4) and consists of trimeric [Cu(SO 4) 2(H 2O) 4] 2? anions, [( R)-C 5H 14N 2] 2+ cations and occluded water molecules. Compound 2 crystallizes in P2 12 12 (No. 18) and contains [Cu(H 2O) 6] 2+ cations, [SO 4] 2? anions and occluded water molecules. The thermal decompositions of compounds 1 and 2 were studied by thermogravimetric analyses and temperature-dependent X-ray diffraction. 相似文献
5.
A one parameter quantum deformation S
μ
L(2, ℂ) of SL(2, ℂ) is introduced and investigated. An analog of the Iwasawa decomposition is proved. The compact part of this decomposition
coincides with S
μ
U(2), whereas the solvable part is identified as a Pontryagin dual of S
μ
U(2). It shows that S
μ
L(2, ℂ) is the result of the dual version of Drinfeld's double group construction applied to S
μ
U(2). The same construction applied to any compact quantum group G
c
is discussed in detail. In particular the explicit formulae for the Haar measures on the Pontryagin dual G
d
of G
c
and on the double group G are given. We show that there exists remarkable 1-1 correspondence between representations of G and bicovariant bimodules (“tensor bundles”) over G
c
. The theory of smooth representations of S
μ
L(2, ℂ) is the same as that of SL(2, ℂ) (Clebsh-Gordon coefficients are however modified). The corresponding “tame” bicovariant bimodules on S
μ
U(2) are classified. An application to 4 D
+ differential calculus is presented. The nonsmooth case is also discussed. 相似文献
6.
N-(1-Anthryl)-2,4,6-trimethyl-pyridinium ( I), N-(2-anthryl)-2,4,6-trimethyl-pyridinium ( II) and 10-(1-anthryl)-1,2,3,4,5,6,7,8-octahydro-acridinium cations ( III) with anomalously high fluorescence Stokes shift have been investigated. Fluorescence kinetics analysis at various temperatures showed that in the range 293–77 K, the radiative deactivation rate constants ( kf) increase by 5.5 to 30 times. The low-temperature time-resolved emission spectra of I–III were found to be consistent with the model: A A* B* where A * is the local excited twisted form and B * is the relaxed more planar, bent conformer of the molecule. The rate constants of the excited relaxed state formation ( k1) and back reaction ( k–1) of compounds studied were estimated. 相似文献
7.
DFT/TDDFT calculations were carried out to investigate the electronic structures, absorption and phosphorescence properties of a series of heteroleptic Ir(III) complexes consisting of two N-heterocyclic carbene ligands and a conjugated bicyclic N,N′-heteroaromatic (N?N) ligand. On the basis of the results reported herein, we attempt to explain the experimental observations according to which complex (mpmi) 2Ir(pybi) ( 1) [Hmpmi = 1-(4-tolyl)-3-methyl-imidazole; Hpybi = 2-(pyridin-2-yl)-1H-benzo[ d]imidazole] emits green light with an extremely high-quantum phosphorescence efficiency (Φ PL ) of 79.3%, while a relatively lower Φ PL (only 11%) was measured for (fpmi) 2Ir(tfpypz) ( 2) [fpmi = 1-(4-fluorophenyl)-3-methylimdazolin-2-ylidene-C, C 2′; tfpypz = 2-(3-(trifluoromethyl)-1H-pyrazol-5-yl)pyridinato] emitting blue light by tuning the N?N ligands. Besides, we also designed (fpmi) 2Ir(pyN3) ( 3) [pyN3H = 2-(5-(trifluoromethyl)-2H-1,2,4-triazol-3-yl)pyridine] and (fpmi) 2Ir(pyN4) ( 4) [pyN4H = 2-(1H-tetrazol-5-yl)pyridine] to explore the influence of electron-withdrawing substituents on N?N ligands on the electronic and optical properties of these Ir(III) complexes. The results revealed that electron-withdrawing substituents can stabilise both HOMOs and LUMOs and induce HOMO–LUMO energy gap change. Moreover, the emission properties can be significantly tuned by introducing different N?N ligands. While new insights were gained on structural and electronic properties, the extremely high Φ PL of 1 was found to be not inherent to spin-orbital coupling effects, but determined by its large transition dipole moment ( μS 1) upon S 0– S 1 transition compared with that of 2. On the basis of these results, the designed complexes 3 and 4 are considered to be the promising candidates for blue-emitting phosphorescence materials with higher Φ PL than the complex 2. 相似文献
8.
Electron paramagnetic resonance study of the single crystals of two PROXYLs, trans-2,5-bis(4-methylphenyl)-2,5-dimethylpyrrolidine-1-oxy [(±)- 1] and trans-2-(4-methylphenyl)-2,5-dimethyl-5-phenylpyrrolidine-1-oxy [(±)- 2] was conducted. The obtained spectra were always fitted well by a single Lorentzian. The principal g-values ( g
x
, g
y
, g
z
) of (±)- 1 and (±)- 2 were determined as (2.00990, 2.00639, 2.00266) and (2.01106, 2.00742, 2.00389), respectively. The profiles of half width
at half maximum (HWHM) depending on two polar angles, θ and ϕ, were measured in all directions. The angular profiles of the
exchange interaction (| J
0|) were attempted to be estimated by dividing the experimental HWHM by the calculated total second moment ( M
2
tot) with the crystallographic data. For (±)- 1, | J
0| along the c-axis was estimated to be much larger than that along the a- or b-axis. This suggests that (±)- 1 is a one-dimensional magnet along the c-axis.
Authors' address: Yohei Noda, Electron Spin Chemistry Laboratory, Department of Chemistry, Graduate School of Science, Kyoto
University, 606-8502 Kyoto, Japan 相似文献
9.
Beam quality factor ( M2) and far-field scattering angle of LD end-pump Nd : YVO 4 laser were measured by slit-scanning method. The experimental results showed that the laser operated on a multi-mode state. The corresponding analytical treatments for slit-scanning method and M2 factor measurement also were presented in this paper. 相似文献
10.
Summary A versatile route to 40-membered library of 2-long alkyl chain substituted benzoazoles ( 1 and 2) and azole[4,5- b]pyridines ( 3 and 4) via microwave-assisted combinatorial synthesis was developed. The reactions were carried out in both monomode and multimode microwave
oven. With the latter, all reactions were performed in high-throughput experimental settings consisting of an 8×5 combinatorial
library designed to synthesize 40 compounds. Each step, from the addition of reagents to the recovery of final products, was
automated. The microwave-assisted N-long chain alkylation reactions of 2-alkyl-1 H-benzimidazole ( 1) and 2-alkyl-1 H-benzimidazole[4,5- b] pyridines ( 3) were also studied. 相似文献
11.
Polymorphism in barium gallate BaGa 2O 4 was studied using electron diffraction and high resolution electron microscopy. Three modifications of BaGa 2O 4 with structures closely related to the high-temperature α-form were observed. The phase transitions from γ-BaGa 2O 4 ( a γ = 18.6143(2) Å = 2<formula><radical><radicand>3</radicand></radical></formula> a α, c γ = 8.6544(1) Å = c α, S.G. P6 3) to β-BaGa 2O 4 ( a β = 2 a α, c β = c α S.G. P6 3) and to the new δ-polymorph having a monoclinic structure ( a δ = c α, b δ = 2 a α + b α, c δ = 2 b α and β ≈ 92°, S.G. P2 1/ c) were induced by electron beam irradiation. High resolution electron microscopy (HREM) observations allow to establish the close similarity between the structures of δ-BaGa 2O 4 and β-SrGa 2O 4. The γ→β and β→δ transitions involve a rearrangement of oxygen atoms in the BaO layers together with a tilting distortion of the tetrahedral framework. The microstructure of the δ-phase is characterised by the presence of numerous translation and orientation domains. 相似文献
13.
A systematically varied series of tetrahedral iridium clusters have been studied using a TDDFT method focusing on their electronic and nonlinear optical properties. The clusters W 2Ir 2(CO) 10(η 5-C 5H 4Me) 2 ( 1), WIr 3(μ-dppe)(CO) 9(η 5-C 5H 4Me ( 2), W 2Ir 2(μ-L)(CO) 8(η 5-C 5H 4Me) 2(L = dppe 3, dppf 4), Ir 4(μ-L)(CO) 10(L = dppm 5, dppe 6, Ph 2P(CH 2) 3PPh 2 7, Ph 2P(CH 2) 4PPh 2 8, (Ph 2P) 2CHMe 9), Ir 4(CO) 10(phen)(phen = 1,10-phenanthroline) ( 10) exhibit the first static hyperpolarizabilities of medium magnitude ( β tot ~ 10 × 10 ?30esu). The origination of β is discussed in terms of the electronic structure calculation and the expanded orbital decomposition scheme. The result suggests the origination of β for all the clusters are mainly d– d electron transitions intra metal skeleton, and d– π* electron transitions from metals to carbonyls. For cluster 5, which contains the ferrocenyl group, the main origination of β involves charge transfer from d orbitals of ferrocene to d orbirals of Ir and W. 相似文献
14.
The utilization of an ionic liquid, [bmim][BF 4] as both reaction medium and promoter for a multi-component reaction of aldehyde ( 1) and 5-amino-3-methyl-1-phenylpyrazole ( 2) with Meldrum acid ( 3) or dimedone ( 5) is studied. From this reaction, pyrazolo[3,4- b]pyridinone ( 4) and pyrazolo[3,4- b]quinolinone ( 6) derivatives were prepared in high yields. This novel procedure showed such advantages as environmentally benign nature,
enhanced efficiency, simple operation process, and mild reaction conditions. As an application, the procedure was successfully
used in the preparation of a set of pyrimidine nucleoside–pyrazolo[3,4- b]pyridine and pyrazolo[3,4- b]quinolinone hybrids with potential biological activities. 相似文献
15.
A group-theoretical analysis is performed for the complete condensation of order parameters at structural phase transitions (SPT's) in the high-temperature superconductors belonging to the D 17 4h -14/mmm space group in the high-symmetry phase. As a rule, such transformations are due to a successive softening of phonons with wave vectors k 1 = 1/2 b 3 and k 2 = 1/2 ( b 1 - b 3) belonging to the K13(X) star of the Brillouin zone of a tetragonal body-centered Bravais cell. SPT's in system La 2-x Ba x CuO 4 are considered in detail. 相似文献
16.
Abstract In the present work, three different solid solutions whose end-members are the orthorhombic sulfates celestite (SrSO 4), barytes (BaSO 4) and anglesite (PbSO 4) are studied using FT-Raman spectroscopy. Sulfate anion symmetric internal modes have been examined in detail by means of band-shape analysis and component fitting procedures. the symmetric stretching mode v1(A1) changes its wavenumber position linearly with the cationic composition of the samples which further confirms the ideal character of the solid solutions studied. the corresponding full-width at half-height is strongly increased in the central components of the different solid solutions which can be understood as an effect of the positional disorder induced by random cationic substitution. Similar results are observed in the symmetric bending mode, v2 (E). the study of the low frequency spectral region permits one to differentiate translational modes of the sulfate anion, which changes its wavenumber position when the alkali-earth metal ion changes from rotational modes. This permits the tentative band assignment of the anglesite rotational Raman bands at 134 and 152 cm ?1, which were previously not assigned. 相似文献
17.
根据密度波理论建立了stage-2有序Li xTiS 2( x=1/8,1/6,1/4,1/3,3/8,1/2)系统的晶胞模型.采用平面波赝势方法,对stage-2有序系统和stage-1有序Li xTiS 2( x=0,1/4,1/3,1/2,2/3,3/4,1)系统进行了几何结构优化和总能量计算,并进行了对比研究.发现stage-2晶胞的参量 c( d
关键词:
xTiS2')" href="#">LixTiS2
阶梯结构
有序—无序相变
第一性原理计算 相似文献
18.
Via the solvothermal reaction between Zn(II) or Mn(II) salts and 5-(3,4-dicarboxylphenoxy)nicotinic acid (H3L) ligand, a trifunctional N,O-building block having three diverse kinds of functional groups (O-ether, N-pyridyl and COOH), two new coordination polymers (CPs) could be generated, and their chemical formulae respectively are {[Mn3(L)2(H2O)2]·4H2O} (1) and {[Zn(HL)]·NMP} (2). The complex 2 based on Zn(II) possesses high efficiency of fluorescence quenching for the nitrophenol (2,4,6-trinitrophenol, TNP; 4-nitrophenol, 4-NP; 3-nitrophenol, 3-NP; 2-nitrophenol, 2-NP) in the aqueous solution. Furthermore, the treatment activity of compounds on the atherosclerosis was assessed, and relevant mechanism was investigated. First of all, the ELISA assay was used to measure the content of the inflammatory cytokines released into the plasma. Besides, the levels of the NF-κb signaling pathway in the vascular endothelial cells were measured with real time RT-PCR. The hemolysis test was conducted in this research to measure the biocompatibility of the new compound. 相似文献
19.
Abstract The 1H‐ and 13C‐NMR spectra of some substituted stilbenes and chalcones were assigned unambiguously on the basis of a combination of homo‐ (COSY) and heteronuclear (HETCOR) two‐dimensional methods, the chemical shifts, as well as spin‐coupling constants. The A ik empirical parameters of the –O–C(S)–N(CH 3) 2, –S–C(O)–N(CH 3) 2, and –SH group were calculated to help predict the chemical shifts of substituted stilbenes, 4′‐nitrostilbenes, and chalcones. The 1H‐ and 13C‐NMR spectra have been shown to be able to differentiate between the isomers of O‐stilbenyl ( 4, 5) and S‐stilbenyl N, N‐dimethylthiocarbamates ( 7, 8) as well as O‐chalconyl ( 6) and S‐chalconyl N, N‐dimethylthiocarbamates ( 9). 相似文献
20.
Neutron-diffraction experiments reveal that ErFe 6Ga 6 forms in the tetragonal ThMn 12-type of structure (space group I 4/mmm). The Fe sublattice orders ferromagnetically below K. The Er moments order antiparallel to the Fe moments which, below about 250 K, leads to a decrease of the total magnetization.
The easy magnetization direction of ErFe 6Ga 6 is perpendicular to the c-axis in the whole temperature range. Refinement at 2 K shows that ErFe 6Ga 6 orders ferrimagnetically with Er moments of 8.5 (2) and Fe moments at the 8( j) site of 1.9 (1) and at the 8( f) site of 1.7 (1) , respectively. At room temperature, ErFe 6Ga 6 exhibits the same type of magnetic order, however with substantially lower Er moments of 1.0 (4) and Fe moments at the 8( f) site of 1.2 (2) . The Fe moments at the 8( j) site amount to 1.9 (5) /Fe.
Received 24 November 1999 and Received in final form 27 March 2000 相似文献
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