| 1. |
- Liu, Haibin, et al.
(författare)
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Asymmetric oxidation of sulfides with hydrogen peroxide catalyzed by a vanadium complex of a new chiral NOO-ligand
- 2009
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Ingår i: Catalysis communications. - : Elsevier BV. - 1566-7367 .- 1873-3905. ; 11:4, s. 294-297
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Tidskriftsartikel (refereegranskat)abstract
- A new chiral NOO-tridentate ligand (8R)-2-(2-hydroxyphenyl)-4-methyl-5,6,7.8-tetrahydro-quinolin-8-ol (1) bearing a rigid tetrahydroquinoline framework was prepared and applied in the vanadium-catalyzed asymmetric oxidation of aryl methyl sulfides with H2O2 as oxidant. Less toxic acetone was found to be the proper solvent for the enantioselective oxidation of sulfides. Under the optimal condition, the asymmetric oxidation of aryl methyl sulfides in acetone catalyzed by VO(acac)(2)/1 at 0 degrees C gives good to high yields (80-95%) of sulfoxides with enantioselectivity up to 77% ee.
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| 2. |
- Fu, Ying, et al.
(författare)
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Energy band structure and spectral gain characteristics of dilute-nitride zinc blende InGaNAs quantum wells embedded in GaAs and GaNAs barriers
- 2006
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 100:7
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Tidskriftsartikel (refereegranskat)abstract
- The spectral gain characteristics of dilute-nitride zinc blende InxGa1-xNyAs1-y quantum wells embedded in GaNy1As1-y1 barriers have been investigated experimentally and theoretically. Two samples, both with the gain peak at 1300 nm, were studied for comparison. One has a high nitrogen concentration in the quantum well with the surrounding barriers being pure GaAs. The other has a lower and uniform nitrogen concentration in the quantum well and the barriers (GaNAs barriers). Measurements show the redshift of the gain peak induced by the incorporation of nitrogen and difference in the spectral gain characteristics. The energy band structures and spectral gain characteristics are analyzed theoretically using the standard eight-band k center dot p theory. It is shown that the introduction of nitrogen atoms in the GaAs barriers reduces the barrier height for the central quantum well so that the energy sublevels in the conduction band becomes condensed. The condensation of the conduction-band energy sublevels reduces the peak gain and makes the gain spectrum narrower, in agreement with measurements.
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| 3. |
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| 4. |
- Hou, Ying, et al.
(författare)
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Carrier wave-packet transport under the influence of charged quantum dot in small-area resonant tunneling diodes
- 2008
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 93:13, s. 132108-
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Tidskriftsartikel (refereegranskat)abstract
- It was shown experimentally that charging InAs quantum dots (QDs) embedded in a small-area GaAs/AlAs double-barrier resonant tunneling diode (RTD) effectively modified the carrier transport properties of the RTD. By adopting and comparing the one-dimensional plane-wave and three-dimensional (3D) wave-packet transport theories we show that the electron transports in the QDRTD device are in the form of 3D wave packets, which are strongly affected by the 3D long-range Coulomb potential induced by charged InAs QDs. This explains well experimental data and indicates that the 3D wave-packet transport model is more appropriate for the QDRTD device.
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| 5. |
- Hou, Ying, et al.
(författare)
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Effects of series and parallel resistances on the current-voltage characteristics of small-area air-bridge resonant tunneling diode
- 2008
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 104:7
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Tidskriftsartikel (refereegranskat)abstract
- We have studied experimentally and theoretically the effects of series and parallel resistances on the current-voltage (I-V) characteristics of the resonant tunneling diode (RTD) in the format of a small-area freestanding air bridge. It has been shown by standard quantum mechanical considerations that the I-V characteristics consists of a simple resonant current peak (without bistability) and the voltage at the current peak is quite low, whereas experiments show not only a much high current-peak voltage, but also the bistability. Furthermore, experimental peak-to-valley ratio is in general quite low. By analyzing material and device structures, it has been demonstrated that the series resistance in the RTD contacts shifts the peak in current to higher voltage, it also creates the experimentally observed bistability effect in the region of the tunneling resonance. The parallel resistance induces a leakage current and reduces the peak-to-valley ratio. We have further performed similar analyses to many RTD structures reported in the literature and the conclusions remain the same.
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| 6. |
- Liu, Hai-Bin, et al.
(författare)
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Synthesis of 3-aryl-5-t-butylsalicylaldehydes and their chiral Schiff base compounds
- 2007
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Ingår i: Synthetic Communications. - : Informa UK Limited. - 0039-7911 .- 1532-2432. ; 37:19-21, s. 3815-3826
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Tidskriftsartikel (refereegranskat)abstract
- Six meta-substituted salicylaldehyde compounds have been prepared in 68-90% yields by the Suzuki-Miyaura coupling reaction using 3-bromo-5-t-butylsalicylaldehyde (la) and arylboronic acids (2a-f) as reactants. Among the obtained products, 3-(4-fluorophenyl)-5-t-butylsalicylaldehyde (3b), 3-(4-methylphenyl)-5-t-butylsalicylaldehyde (3d), 3-(1-naphthyl)-5-t-butylsalicylaldehyde (3e), and 3-(2-naphthyl)-5-t-butylsalicylaldehyde (3f) have not been reported so far. A series of new Schiff base ligands (L1-L10) were obtained in 51-89% yields from these salicylaldehyde derivatives.
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| 7. |
- Liu, Haibin, et al.
(författare)
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Influence of substituents in the salicylaldehyde-derived Schiff bases on vanadium-catalyzed asymmetric oxidation of sulfides
- 2008
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Ingår i: Applied organometallic chemistry. - : Wiley. - 0268-2605 .- 1099-0739. ; 22:5, s. 253-257
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Tidskriftsartikel (refereegranskat)abstract
- A series of chiral Schiff bases (L-1-L-5) with different substituents in the salicylidenyl unit were prepared from condensation of 3-aryl-5-tert-butylsalicylaldehyde derivatives and optically active amino alcohols. Bromination of 3-phenyl-5-tert-butylsalicylaldehyde gave an unexpected product 3-(4-bromophenyl)-5-bromosalicylaldehyde, from which the corresponding Schiff base ligands L-6 and L-7, derived from (S)-valinol and (S)-tert-leucinol, respectively, were prepared. Ligands L-1-L-7 were applied to the vanadium-catalyzed asymmetric oxidation of aryl methyl sulfides. Under the optimal conditions, the oxidation of the thioanisole with H2O2 as oxidant in CH2Cl2 catalyzed by VO(acac)(2)-L-1-L-7 gives good yields (74-83%) with moderate enantioselectivity (58-77% ee). Ligand L-7, containing a 4-bromophenyl group on the 3-position and a Br atom on the 5-position of the salicylidenyl moiety, displays an 80-90% ee for vanadium-catalyzed oxidation of methyl 4-bromophenyl sulfide and methyl 2-naphthyl sulfide.
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| 8. |
- Normand, Philippe, et al.
(författare)
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Genome characteristics of facultatively symbiotic Frankia sp. strains reflect host range and host plant biogeography.
- 2007
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Ingår i: Genome Research. - : Cold Spring Harbor Laboratory. - 1088-9051. ; 17:1, s. 7-15
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Tidskriftsartikel (refereegranskat)abstract
- Soil bacteria that also form mutualistic symbioses in plants encounter two major levels of selection. One occurs during adaptation to and survival in soil, and the other occurs in concert with host plant speciation and adaptation. Actinobacteria from the genus Frankia are facultative symbionts that form N2-fixing root nodules on diverse and globally distributed angiosperms in the "actinorhizal" symbioses. Three closely related clades of Frankia sp. strains are recognized; members of each clade infect a subset of plants from among eight angiosperm families. We sequenced the genomes from three strains; their sizes varied from 5.43 Mbp for a narrow host range strain (Frankia sp. strain HFPCcI3) to 7.50 Mbp for a medium host range strain (Frankia alni strain ACN14a) to 9.04 Mbp for a broad host range strain (Frankia sp. strain EAN1pec.) This size divergence is the largest yet reported for such closely related soil bacteria (97.8%–98.9% identity of 16S rRNA genes). The extent of gene deletion, duplication, and acquisition is in concert with the biogeographic history of the symbioses and host plant speciation. Host plant isolation favored genome contraction, whereas host plant diversification favored genome expansion. The results support the idea that major genome expansions as well as reductions can occur in facultative symbiotic soil bacteria as they respond to new environments in the context of their symbioses.
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| 9. |
- Wang, Chao-Jie, et al.
(författare)
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Clinicopathological significance of microRNA-31, -143 and -145 expression in colorectal cancer
- 2009
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Ingår i: Disease Markers. - 0278-0240 .- 1875-8630. ; 26:1, s. 27-34
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Tidskriftsartikel (refereegranskat)abstract
- We are just beginning to understand how microRNAs (miRNAs) are involved in tumor-related processes in humans. Applying real-time RT-PCR, we investigated the miR-31, miR-143 and miR-145 expression in 98 primary CRC specimens, along with the corresponding normal mucosa specimens, and analyze the relationship of their expression with clinicopathological features. Our results showed the miR-31 expression was up-regulated in CRC compared to normal mucosa (p = 0.001). Furthermore, miR-31 expression was positively related to advanced TNM stage (p = 0.026) and deeper invasion of tumors (p = 0.024). MiR-145 was down-regulated in both colon (p = 0.001) and rectal (p = 0.012) cancer. MiR-143 was only down-regulated in colon cancer (p = 0.023) but not in rectal cancer (p = 0.351). There was no relationship of miR-143 and miR-145 expression with other clinicopathological features (p > 0.05), except that the miR-145 expression was related to cancer site (p = 0.03). In conclusion, the miR-31 overexpression may be involved in the development and progression of CRC. The miR-143 and miR-145 may play a certain role in the development of colon and/or rectal cancers but not in progression of the disease.
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| 10. |
- Wang, Sheng-Jun, 1981-, et al.
(författare)
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Influence of synaptic interaction on firing synchronization and spike death in excitatory neuronal networks
- 2008
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Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - New York : American Physical Society through the American Institute of Physics. - 1063-651X .- 1095-3787. ; 78:6, s. 061906-
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the influence of efficacy of synaptic interaction on firing synchronization in excitatoryneuronal networks. We find spike death phenomena: namely, the state of neurons transits from the limit cycleto a fixed point or transient state. The phenomena occur under the perturbation of an excitatory synapticinteraction, which has a high efficacy. We show that the decrease of synaptic current results in spike deaththrough depressing the feedback of the sodium ionic current. In the networks with the spike death property thedegree of synchronization is lower and insensitive to the heterogeneity of neurons. The mechanism of theinfluence is that the transition of the neuron state disrupts the adjustment of the rhythm of the neuronsoscillation and prevents a further increase of the firing synchronization.
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