The orbital scale evolution of regional climate recorded in a long sediment core from Heqing；China

IEECAS SKLLQG

Medium-spin states in Ge-70 and the role of the g(9/2) orbital

Medium-spin states of Ge-70 have been studied via the Ni-60(C-12,2p gamma)Ge-70 reaction at 45 MeV. The ground-state band and the second 0(+) band have been extended to the 12(+) and 8(+) states, respectively. Two negative-parity bands, one of which has a coupled structure and the other has a decoupled structure, have been observed additionally. Although the latter decoupled structure was known up to the (21(-)) state from a previous experiment, the part of the level scheme up to the 15(-) state has been largely modified by the present experiment. Backbendings observed in the positive- and negative-parity yrast bands have been compared with those of the neighboring even Ge isotopes. The experimental level structure has been compared with the shell-model calculations in the model space (2p(3/2), 1f(5/2), 2(p1/2), 1g(9/2)) employing two kinds of effective interactions, one of which is an extended P + QQ interaction with monopole interactions and the other is developed from a renormalized G matrix. Microscopic structures of the observed bands have been discussed with the help of the shell-model calculations.

Non-relativistic conformal symmetries in fluid mechanics

The symmetries of a free incompressible fluid span the Galilei group, augmented with independent dilations of space and time. When the fluid is compressible, the symmetry is enlarged to the expanded Schrodinger group, which also involves, in addition, Schrodinger expansions. While incompressible fluid dynamics can be derived as an appropriate non-relativistic limit of a conformally invariant relativistic theory, the recently discussed conformal Galilei group, obtained by contraction from the relativistic conformal group, is not a symmetry. This is explained by the subtleties of the non-relativistic limit.

Magnetic structure and orbital ordering in tetragonal and monoclinic KCrF3 from first-principles calculations

KCrF3 has been systematically investigated by using the full-potential linearized augmented plane wave plus local orbital method within the generalized gradient approximation and the local spin density approximation plus the on-site Coulomb repulsion approach. The total energies for ferromagnetic and three different antiferromagnetic configurations are calculated in the high-temperature tetragonal and low-temperature monoclinic phases, respectively.

Charge, orbital, and magnetic ordering in YBaFe2O5 from first-principles calculations

First principles calculations using the augmented plane wave plus local orbitals method, as implemented in the WIEN2k code, have been used to investigate the electronic and magnetic properties of YBaFe2O5, especially as regards the charge-orbital ordering. Although the total 3d charge disproportion is rather small, an orbital order parameter defined as the difference between t(2g) orbital occupations of Fe2+ and Fe3+ cations is large (0,73) and gives unambiguous evidence for charge and orbital ordering: Strong hybridization between O 2p and Fe e(g) states results in the nearly complete loss of the separation between the total charges at the Fe2+ and Fe3+ atoms.

Orbital ordering in Cs2AgF4 from first principles

First-principles calculations using the augmented plane wave plus local orbital method, as implemented in the WIEN2K code, have been used to investigate the structural, electronic, and magnetic properties of the layered perovskite Cs2AgF4. Our calculations indicate that an orthorhombic ground state for Cs2AgF4 is energetically favored over tetragonal. We also find that Cs2AgF4 should be a strong two-dimensional ferromagnet, with very weak antiferromagnetic coupling between the layers, in agreement with the experiment. More importantly, an antiferrodistortive ordering of z(2)-x(2) and z(2)-y(2) orbitals is inferred from the density of states and from a spin density isosurface analysis.

X-ray crystal structure and molecular mechanics calculations of (2,6-iso-dipropyl-phenylamide) dimethyl (tetra-methylcyclopenta-dienyl) silane titanium dichloride

Crystal and molecular structure of (2.6-dipropylphenylamide) dimethyl (tetra-methyl cyclopentadienyl) silane titanium dichloride (I) was fully characterized by X-ray diffraction. The crystal is obtained from a mixture of ether/hexane as orthorhombic. with a = 12.658 (3) Angstrom. b = 16.62 (3) Angstrom. c = 11.760 (2) Angstrom. V = 2474.2 (9) Angstrom(3). Z = 4, space group Pnma. R = 0.0399; Componud I compose of the pi-bounded ring with its dimethylsilyl-dipropyl phenyl amido group and the two terminal chloride atoms coordinated to central metal to form a so-called constrained geometry catalyst (CGC) structure. The result of molecular mechanics (MM) calculations on compound I shows that bond lengths and bond angles from the MM calculation are comparable to the data obtained from the X-ray diffraction study. The relation of the structure of CGCs and their catalytic activity by MM calculations is also discussed.

STUDY ON BONDING AND 4F ORBITAL EFFECT OF LANTHANIDE COMPOUNDS

The bonding and the 4f orbital effect of lanthanide elements at different valence state in their compounds have been studied by INDO method in this paper. The results obtained show that the bonding of lanthanide compounds is affected by many factors, such as valence state, ionic radius, ligand, coordinate number, space configuration etc. The strength of bonds composed of different ligands with lanthanide is distinctly different. The covalence of Ln-L bonds of lanthanide ions at high valence state in their compounds is larger than that at low valence state, The covalency at low coordinate number is larger than that at high coordinate number. Some lanthanide compounds with special configuration, besides sigma-bond, can form p(pi)-d(pi) dative bond with much overlap, which makes the Ln-L bond increase markedly. The effect of 4f orbitals on bonding is far less than that of 5d orbitals. The Ln 4f orbitals at 3 or 2 valence state may be considered to be essentially localized, while the contribution of 4f orbitals on bonding in 4 valent cerium compounds increases obviously, up to 1%.

EFFECT OF REPTATION ON FRACTURE-MECHANICS OF RUBBER NETWORKS

End-linked hydroxyl-terminated polybutadiene containing unattached linear polybutadiene was used to study the effect of reptating species on the fracture mechanics of rubber networks. The concentration of reptating species in the networks ranged from 0 to 100%. The fracture mechanics of the networks was described using the critical strain energy release rate in mode III testing, i.e. the tearing energy. The tearing energy was measured at room temperature using a 'trouser' specimen at a strain rate spanning five logarithmic decades. When the strain rate was as low as 10(-4) s-1, the tearing energy of the networks increased with reduction in reptating species. In this case the reptating species did not contribute to the tearing energy of the networks due to relaxation. Hence, the tearing energy increased with the number of crosslinked chains per unit volume in the networks. At a strain rate ranging from 10(-3) to 10(-1) s-1, the tearing energy of the networks was governed by local viscosity. The tearing energies of the networks containing various amounts of reptating species were superimposed to give a master curve based on the Williams-Landel-Ferry equation.

A study of a molecular mechanics field used in simulating enantiorecognition

A molecular mechanics field, Alchemy II, was utilized to model the chiral recognition between S-N-acetyl-alpha-methyl-alpha-naphthylamine and (R, S)-N-(3, 5-dinitrophrnyl)-alpha-methyl-benzeneacetamide and between beta-cyclodextrin and (R, S)-fenoprofen. Some preliminary results have: been obtained to sustain the three-point action models and the induce-fit action in enantiorecognition.