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951.
952.
The binding of heterobidentate P∧S ligands introduces metal-centered chirality to the planar chiral parent complex Ru(η6:η1-NMe2C6H4C6H4PCy2)Cl2. Observed diastereomeric ratios for the kinetic product vary dramatically depending upon ring size of the chelate formed with the P∧S ligand. The complexes epimerize very slowly to thermodynamic product ratios that are substantially different from the kinetic product ratios. 相似文献
953.
A route to the total synthesis of koumine has been suggested. Five 4-substituted 1, 2-d hydropyridine derivatives, which are supposed to be a conjugated diene of Diels-Alder reaction to produce the isoquinuclidine ring of koumine, have been synthesized. Only two of them were found to be able to undergo the Diels-Alder reaction. The stereochemistry of the reaction product has also been examined. 相似文献
954.
955.
J. Mass M. Avella J. Jimnez M. Callahan E. Grant K. Rakes D. Bliss B. Wang 《Superlattices and Microstructures》2007,42(1-6):306
Understanding the luminescence of ZnO is very important for some applications. In spite of the many studies carried out, there are still some points concerning the origin of some of the luminescence emissions in ZnO crystals that require additional study; in particular, the role of extended defects remains to be a matter of controversy. We present here a cathodoluminescence analysis of the defects generated by Vickers indentation in hydrothermal HTT crystals. Special emphasis was paid to the luminescence band peaking around 3.3 eV. The origin of this band is a matter of controversy, since it has been related to different causes, extended defects being one of the candidates for this emission. The CL images were acquired around crystal defects. It is observed that the 3.3 eV emission is enhanced around the crystal defects; though it is also observed, but weaker, out of the defect regions, which suggests that there exist two luminescence emissions peaking very close to 3.3 eV. The two emissions, one related to structural defects and the other to the LO phonon replica of the free excitonic band, appear very close each other and their relative intensity should determine the shape of the spectrum. 相似文献
956.
王登银 《数学物理学报(B辑英文版)》2007,27(2):317-328
All parabolic subgroups and Borel subgroups of PΩ(2m 1, F) over a linear-able field F of characteristic 0 are shown to be complete groups, provided m > 3. 相似文献
957.
N. Chai W.D. Kulatilaka S.V. Naik N.M. Laurendeau R.P. Lucht J.P. Kuehner S. Roy V.R. Katta J.R. Gord 《Applied physics. B, Lasers and optics》2007,88(1):141-150
We report the application of electronic-resonance-enhanced coherent anti-Stokes Raman scattering (ERE-CARS) for measurements
of nitric oxide concentration ([NO]) in three different atmospheric pressure flames. Visible pump (532 nm) and Stokes (591 nm)
beams are used to probe the Q-branch of the Raman transition. A significant resonance enhancement is obtained by tuning an
ultraviolet probe beam (236 nm) into resonance with specific rotational transitions in the (v’=0, v”=1) vibrational band of
the A2Σ+–X2Π electronic system of NO. ERE-CARS spectra are recorded at various heights within a hydrogen-air flame producing relatively
low concentrations of NO over a Hencken burner. Good agreement is obtained between NO ERE-CARS measurements and the results
of flame computations using UNICORN, a two-dimensional flame code. Excellent agreement between measured and calculated NO
spectra is also obtained when using a modified version of the Sandia CARSFT code for heavily sooting acetylene-air flames
(φ=0.8 to φ=1.6) on the same Hencken burner. Finally, NO concentration profiles are measured using ERE-CARS in a laminar,
counter-flow, non-premixed hydrogen-air flame. Spectral scans are recorded by probing the Q1 (9.5), Q1 (13.5) and Q1 (17.5) Raman transitions. The measured shape of the [NO] profile is in good agreement with that predicted using the OPPDIF
code, even without correcting for collisional effects. These comparisons between [NO] measurements and predictions establish
the utility of ERE-CARS for detection of NO in flames with large temperature and concentration gradients as well as in sooting
environments.
PACS 07.88.+y; 42.62.Fi; 42.65.Dr 相似文献
958.
959.
X.P. Hu X. Wang Z. Yan H.X. Li J.L. He S.N. Zhu 《Applied physics. B, Lasers and optics》2007,86(2):265-268
High power red light was generated from a periodically-poled stoichiometric LiTaO3 (PPSLT) by single-pass frequency doubling of a diode-side-pumped, Q-switched Nd:YAG laser at 1319 nm. An average power of
2.4 W of the 660 nm red light was obtained at the fundamental power of ∼5.4 W with the conversion efficiency up to 44.4% and
with low fluctuation down to 2%. The high efficiency and stability at the red output indicate that it is a practical method
to construct a reliable compact red laser.
PACS 42.70.Mp; 42.79.Nv; 42.55.Xi 相似文献
960.
S.-Y. Lee T.-H. Kim D.-I. Suh E.-K. Suh N.-K. Cho W.-K. Seong S.-K. Lee 《Applied Physics A: Materials Science & Processing》2007,87(4):739-742
We demonstrate GaN nanowire (NW) current rectifiers which were formed by assembling n-GaN nanowires on a patterned p-Si substrate
by means of alternating current (ac) dielectrophoresis. The dielectrophoresis was accomplished at a frequency of 10 kHz with
three different ac bias voltages (5, 10, and 15 Vp–p), indicating that the number of aligned GaN nanowires increased with increasing ac bias voltage. The n-GaN NW/p-Si diodes
showed well-defined current rectifying behavior with a forward voltage drop of 1.2–1.5 V at a current density of 200 A/cm2. We observed that the GaN NW diode functioned well as a half-wave rectifier.
PACS 71.20.Nr; 73.40.Cg; 73.40.Ei; 73.40.Kp 相似文献