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81.
82.
本文根据Brouwer映射度的理论和微分拓扑的基本方法推广了Lusternik_Schnirelmann定理 相似文献
83.
Lang J Sloop DJ Lin TS 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2005,176(2):4731-256
We report a new technique to map the orientational anisotropy of paramagnetic systems without physically changing the crystal orientations in near zero-field (NZF) pulsed EPR experiments. By implementing three sets of orthogonal coils around the sample, we are ble to create a magnetic vector up to 2 mT in any three-dimensional orientation in space. In NZF region, the hyperfine tensor elements are comparable to the electronic Zeeman interaction energy, thus very rich spectral patterns can be obtained by "dialing" in a magnetic field vector without moving the sample. The technique further allows us to examine the site symmetry of organic crystals and powdered solids doped with chromophores which can be photo-excited to the triplet state by laser light. The technique is exemplified in the study of pentacene in p-terphenyl crystals. 相似文献
84.
85.
In order to gain insight into the formamide molecule, seven tautomers and twelve transition states are found after being modeled by the density function theory of Becke's three-parameter hybride (B3LYP) type and ab initio Möller–Plesset second-order perturbation (MP2)-type methods. The isomerization phenomena between enol-keto tautomers and transition states via internal rotation or the proton transfer process are surveyed. A localized analysis is also introduced to ascertain the bond character caused by the delocalization of electrons, which will force the formamide tautomers to become planar. The trans effect in the molecule increases molecular stability. 相似文献
86.
Subunit rotation models activation of serotonin 5-HT<Subscript>3AB</Subscript> receptors by agonists
The N-terminal extracellular regions of heterooligomeric 3AB-type human 5-hydroxytryptamine receptors (5-HT3ABR) were modelled based on the crystal structure of snail acetylcholine binding protein AChBP. Stepwise rotation of subunit A by 5 degrees was performed between -10 degrees and 15 degrees to mimic agonist binding and receptor activation. Anticlockwise rotation reduced the size of the binding cavity in interface AB and reorganised the network of hydrogen bonds along the interface. AB subunit dimers with different rotations were applied for docking of ligands with different efficacies: 5-HT, m-chlorophenylbiguanide, SR 57227, quinolinyl piperazine and lerisetron derivatives. All ligands were docked into the dimer with -10 degrees rotation representing ligand-free, open binding cavities similarly, without pharmacological discrimination. Their ammonium ions were in hydrogen bonding distance to the backbone carbonyl of W183. Anticlockwise rotation and contraction of the binding cavity led to distinctive docking interactions of agonists with E129 and cation-pi interactions of their ammonium ions. Side chains of several further amino acids participating in docking (Y143, Y153, Y234 and E236) are in agreement with the effects of point mutations in the binding loops. Our model postulates that 5-HT binds to W183 in a hydrophobic cleft as well as to E236 in a hydrophilic vestibule. Then it elicits anticlockwise rotation to draw in loop C via pi-cation-pi interactions of its ammonium ion with W183 and Y234. Finally, closure of the binding cavity might end in rebinding of 5-HT to E129 in the hydrophilic vestibule. 相似文献
87.
For a dense G-set of parameters, the irrational rotation algebrais shown to contain infinitely many C*-subalgebras satisfyingthe following properties. Each subalgebra is isomorphic to adirect sum of two matrix algebras of the same (perfect square)dimension; the Fourier transform maps each summand onto theother; the corresponding unit projection is approximately central;the compressions of the canonical generators of the irrationalrotation algebra are approximately contained in the subalgebra.2000 Mathematics Subject Classification 46L80, 46L40, 46L35. 相似文献
88.
A theoretical model has been developed to account for certain features of both newly observed and previously reported CH3-bending subbands between 1450 and 1570 cm−1 in the high-resolution Fourier transform infrared spectrum of CH3OH [Can. J. Phys. 79 (2001) 435]. The features include (i) an apparent inversion of the rotationless E-A torsional splitting with respect to the ground state, i.e., the A state located above the E state, (ii) a pronounced upward slope in the K-reduced torsion-vibration energy pattern for the subband origins, and (iii) unexpected A1/A2 inversion of the K=2A and K=3AJ-rotational levels that led to ambiguity in identifying the vibrational mode as or . The model is an effective internal coordinate Hamiltonian constructed in G6 molecular symmetry with the CH3-bends coupled to each other and to torsion and including a- and γ-type Coriolis coupling. With this model, 33 out of 36 experimental upper-state K-term values for newly assigned , and ν10 subbands plus previous ν4 subbands have together been fitted successfully, employing 9 adjustable parameters and 17 fixed parameters to give a standard deviation of 0.14 cm−1. The Pγ Coriolis term appears to be the leading cause of the upward shift in the K-reduced energies. When J-dependence is introduced via a rotational Hamiltonian including b- and c-type Coriolis terms in addition to molecular asymmetry, the observed A1/A2 inversion of the K=2A and 3A rotational levels can also be reproduced. Predictions using the fitted K-rotation-torsion-vibration Hamiltonian show an interesting Coriolis-induced crossover and mixing of the ν5 and ν10 torsion-vibration energy patterns. These predictions played a role in identifying two of the new ν5 subbands in the crossing region, thereby helping to validate the model. 相似文献
89.
The rotational spectra of o-fluorotoluene and its seven 13C isotopic species were recorded in the frequency range from 4 to 20 GHz with employment of pulsed molecular beam Fourier-transform microwave (MB-FTMW) spectrometers. The analysis of the spectra in the two lowest states of methyl internal rotation (torsional ground state, A and E species) was based on a asymmetric frame-rigid symmetric top Hamiltonian with inclusion of centrifugal distortion terms, yielding structural rotational constants, as well as the threefold barrier V
3 to internal rotation and the angle(a,i) between the principal moment of inertia a axis and the internal rotor axis i. The rotational constants of all eight isotopomeres were used to derive the seven 13C r
s
coordinates of the molecule. 相似文献
90.
Two-center nuclear attraction integrals over Slater type orbitals with integer and noninteger principal quantum numbers in nonlined up coordinate systems have been calculated by means of formulas in our previous work (T. Özdoan and M. Orbay, Int. J. Quant. Chem. 87 (2002) 15). The computer results for integer case are in best agreement with the prior literature. On the other hand, the results for noninteger case are not compared with the literature due to the scarcity of the literature, but also compared with the limit of integer case and good agreements are obtained. The proposed algorithm for the calculation of two-center nuclear attraction integrals over Slater type orbitals with noninteger principal quantum numbers in nonlined-up coordinate systems permits to avoid the interpolation procedure used to overcome the difficulty introduced by the presence of noninteger principal quantum numbers. Finally, numerical aspects of the presented formulae are analyzed under wide range of quantum numbers, orbital exponents and internuclear distances. 相似文献