排序方式: 共有29条查询结果,搜索用时 31 毫秒
1.
2.
Drift mobility measurements in melt-grown BaTiO3 single crystal have been performed using the Spear method. The mobility of (3 ± 1) × 10?3 cm2V?1 sec?1 at room temperature is found to be thermally activated, with an activation energy of 0.15 ± 0.04 eV. Two interpretations are investigated to explain these results: trapping effects due to oxygen vacancies or small polaron hopping. 相似文献
3.
Background
Parkinson's disease, a prevalent neurodegenerative disease, is characterized by the reduction of dopaminergic neurons resulting in the loss of motor control, resting tremor, the formation of neuronal inclusions and ultimately premature death. Two inherited forms of PD have been linked to mutations in the α-synuclein and parkin genes. The parkin protein functions as an ubiquitin ligase targeting specific proteins for degradation. Expression of human α-synuclein in Drosophila neurons recapitulates the loss of motor control, the development of neuronal inclusions, degeneration of dopaminergic neurons and the ommatidial array to provide an excellent genetic model of PD.Results
To investigate the role of parkin, we have generated transgenic Drosophila that conditionally express parkin under the control of the yeast UAS enhancer. While expression of parkin has little consequence, co-expression of parkin with α-synuclein in the dopaminergic neurons suppresses the α-synuclein-induced premature loss of climbing ability. In addition directed expression of parkin in the eye counteracts the α-synuclein-induced degeneration of the ommatidial array. These results show that parkin suppresses the PD-like symptoms observed in the α-synuclein-dependent Drosophila model of PD.Conclusion
The highly conserved parkin E3 ubiquitin ligase can suppress the damaging effects of human α-synuclein. These results are consistent with a role for parkin in targeting α-synuclein to the proteasome. If this relationship is conserved in humans, this suggests that up-regulation of parkin should suppress α-synucleinopathic PD. The development of therapies that regulate parkin activity may be crucial in the treatment of PD.4.
The phase behavior of rod-plate mixtures was investigated using model systems containing unambiguously rod- and plate-shaped colloids. We find that the theoretically disputed biaxial nematic phase is unstable with respect to demixing into an isotropic and two uniaxial nematic phases. The phase behavior at very high densities is exceptionally rich and includes the coexistence of up to four different liquid crystalline phases, which stem from the coupling between the employed particle shapes and polydispersity. 相似文献
5.
P. Dougan Dr. T. Kivikas FM K. Lugnér V. Ramsay W. Stiefler 《Zeitschrift für Physik A Hadrons and Nuclei》1976,276(1):55-64
The cross-sections for deuteron photo-disintegration have been measured at nine c.m. angles from 37 to 143 degrees. The minimum and maximum photon energies have been 139 and 832 MeV respectively. The results are in agreement with earlier data above 300 MeV, but are significantly larger below 200 MeV, the discrepancies being up to 50% at the lowest energies measured. 相似文献
6.
The electronic structures of SrTiO3 crystals doped with Fe3+, Fe4+ and Fe5+ ions have been investigated using the Xα cluster approach. The ground-state eigenvalues show the lower Fe acceptor level, of t2g↓ symmetry, localized inside the SrTiO3 band gap, respectively at 2.8 eV above the valence band edge. Other acceptor levels, with eg↓ and eg↑ symmetries, appear inside the gap when the Fe nominal ionicity increases.The theoretical Xα excitation energies of O 2p-Fe 3d transitions confirms the experimental interpretations of acceptor charge transfer bands for the optical absorption spectra of SrTiO3:Fe4+ and SrTiO3:Fe5+ crystals.The large optical excitation energies compared with the thermal transitions are partly due to the O 2p band width. 相似文献
7.
8.
F.M. Michel-Calendini L. Hafid G. Godefroy H. Chermette 《Solid State Communications》1985,54(11):951-956
Molecular orbital calculations relevant to TiO68- and FeO69- clusters are carried out in the Oh and C4v symmetries in order to represent the electronic structures of pure and iron doped BaTiO3 crystals in the cubic and tetragonal phases. The spontaneous polarization Ps is computed from the ground-state electronic distributions. The band gap anisotropy and the band edge polarization potentials are calculated and compared to experiment. 相似文献
9.
10.
Célia?Fonseca?Guerra Tushar?van der?Wijst F.?Matthias?BickelhauptEmail author 《Structural chemistry》2005,16(3):211-221
We have theoretically analyzed Watson–Crick AT and GC base pairs in which purine C8 and/or pyrimidine C6 positions carry a substituent X = H, F, Cl or Br, using the generalized gradient approximation (GGA) of density functional theory at BP86/TZ2P. The purpose is to study the effects on structure and hydrogen bond strength if X = H is substituted by a halogen atom. Furthermore, we wish to explore the relative importance of electrostatic attraction versus orbital interaction in the above multiply hydrogen-bonded systems, using a quantitative bond energy decomposition scheme. We find that replacing X = H by a halogen atom has relatively small yet characteristic effects on hydrogen bond lengths, strengths and bonding mechanism. In general, it reduces the hydrogen-bond-accepting- and increases the hydrogen-bond-donating capabilities of a DNA base. The orbital interaction component in these hydrogen bonds is found for all substituents (X = H, F, Cl, and Br) to contribute about 41% of the attractive interactions and is thus of the same order of magnitude as the electrostatic component, which provides the remaining 59% of the attraction. 相似文献