排序方式: 共有25条查询结果,搜索用时 31 毫秒
1.
GaN samples, containing various concentrations of carbon and doped intentionally with silicon, have been grown heteroepitaxially on sapphire using metal-organic-chemical-vapor deposition. Previous electrical and optical data, together with Density Functional calculations, have suggested that carbon is incorporated at acceptor and donor substitutional sites in this material; the relative importance of each is determined by the Fermi level position and the growth conditions. Here the luminescence behavior of these materials is examined in more detail, including spectral, temperature, and time dependences under ultraviolet light and electron beam excitation conditions. Particular attention is given to the commonly observed “yellow band” at , a blue luminescence at seen only in samples where carbon is the majority dopant, and ultraviolet bands near . Our data suggest that the latter two bands are both donor-acceptor related with the final state being the negatively charged state of a carbon atom substituting for nitrogen. In samples where carbon is the majority dopant, extended luminescence excitation at low temperatures results in large changes in the brightness of the yellow and blue luminescence bands. These effects are similar to other recent observations of luminescence metastability in high resistivity GaN, and we suggest that carbon plays a crucial role in this phenomenon. 相似文献
2.
Trent D Lund Timothy W West Lilyan Y Tian Lihong H Bu Daniel L Simmons Kenneth DR Setchell Herman Adlercreutz Edwin D Lephart 《BMC neuroscience》2001,2(1):20-13
Background
In learning and memory tasks, requiring visual spatial memory (VSM), males exhibit superior performance to females (a difference attributed to the hormonal influence of estrogen). This study examined the influence of phytoestrogens (estrogen-like plant compounds) on VSM, utilizing radial arm-maze methods to examine varying aspects of memory. Additionally, brain phytoestrogen, calbindin (CALB), and cyclooxygenase-2 (COX-2) levels were determined. 相似文献3.
4.
5.
Melissa D'Ascenzio Kathryn M. Pugh Rebecca Konietzny Georgina Berridge Cynthia Tallant Shaima Hashem Octovia Monteiro Jason R. Thomas Markus Schirle Stefan Knapp Brian Marsden Oleg Fedorov Chas Bountra Benedikt M. Kessler Paul E. Brennan 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(4):1019-1024
6.
Peter G. K. Clark Dr. Lucas C. C. Vieira Dr. Cynthia Tallant Dr. Oleg Fedorov Dr. Dean C. Singleton Dr. Catherine M. Rogers Octovia P. Monteiro James M. Bennett Dr. Roberta Baronio Dr. Susanne Müller Dr. Danette L. Daniels Jacqui Méndez Prof. Dr. Stefan Knapp Dr. Paul E. Brennan Prof. Dr. Darren J. Dixon 《Angewandte Chemie (International ed. in English)》2015,54(21):6217-6221
The bromodomain‐containing proteins BRD9 and BRD7 are part of the human SWI/SNF chromatin‐remodeling complexes BAF and PBAF. To date, no selective inhibitor for BRD7/9 has been reported despite its potential value as a biological tool or as a lead for future therapeutics. The quinolone‐fused lactam LP99 is now reported as the first potent and selective inhibitor of the BRD7 and BRD9 bromodomains. Development of LP99 from a fragment hit was expedited through balancing structure‐based inhibitor design and biophysical characterization against tractable chemical synthesis: Complexity‐building nitro‐Mannich/lactamization cascade processes allowed for early structure–activity relationship studies whereas an enantioselective organocatalytic nitro‐Mannich reaction enabled the synthesis of the lead scaffold in enantioenriched form and on scale. This epigenetic probe was shown to inhibit the association of BRD7 and BRD9 to acetylated histones in vitro and in cells. Moreover, LP99 was used to demonstrate that BRD7/9 plays a role in regulating pro‐inflammatory cytokine secretion. 相似文献
7.
8.
Boren B Hirschi JS Reibenspies JH Tallant MD Singleton DA Sulikowski GA 《The Journal of organic chemistry》2003,68(23):8991-8995
Diels-Alder reactions of vinylazepines with N-phenylmaleimide afforded exclusively the exo cycloadduct, while high endo stereoselectivity was observed, as previously reported, in analogous reactions of vinylpiperideines. This curious contrast was confirmed by X-ray analysis of cycloadducts not susceptible to epimerization. The stereoselectivity of Diels-Alder reactions of vinylazepines, vinylpiperideines, and vinylcycloalkenes exhibits surprising divergence depending on the detailed diene structure, and DFT calculations (Becke3LYP) were undertaken to shed light on these observations. The model calculations correctly predict the major stereoisomers in these reactions, though they tend to significantly underestimate the stereoselectivity. The results suggest some general considerations in predicting or controlling the stereochemistry of this class of Diels-Alder reactions. 相似文献
9.
Glasses in the Na2OSiO2Sc2O3 system have been studied by Raman and difference Raman spectroscopy. Addition of Sc2O3 to sodium silicate glasses results in new vibrational bands at 1025 cm?1 and 360 cm?1. The high frequency band is interpreted to be due to Sc+3 quasi-complexes formed by Sc+3 ions coordinated by SiO4?4 tetrahedra having non-bridging oxygens. The discrete character of the scandium-produced bands implies incipient separation of Sc+3-enriched silicate structures from purely silicate structures. 相似文献
10.
DR.G. Domairry A. Mohsenzadeh M. Famouri 《Communications in Nonlinear Science & Numerical Simulation》2009,14(1):85-95
In this paper Jeffery–Hamel flow has been studied and its nonlinear ordinary differential equation has been solved through homotopy analysis method (HAM). The obtained solution in comparison with the numerical ones represents a remarkable accuracy. The results also indicate that HAM can provide us with a convenient way to control and adjust the convergence region. 相似文献