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See detailE-b-farnesene synergizes the influence of an insecticide to improve control of cabbage aphids in China
Cui, L.L; Dong, J.; Francis, Frédéric ULg et al

in Crop Protection (2012)

Extensive use of pesticides to control insect pests can have negative effects on the environment, natural enemies and food safety. The aphid alarm pheromone, E-b-farnesene (Ebf), appears to hold strong ... [more ▼]

Extensive use of pesticides to control insect pests can have negative effects on the environment, natural enemies and food safety. The aphid alarm pheromone, E-b-farnesene (Ebf), appears to hold strong potential for controlling a wide variety of aphid pests. To understand the control potential of Ebf, we used field experiments in a factorial design to test its influence and that of the insecticide imidacloprid on populations of aphids Lipaphis erysimi (Kaltenbach) and Myzus persicae (Sulzer) on Chinese cabbage, Brassica rapa pekinensis (Brassicales: Brassicaceae). Our results showed imidacloprid treatment alone can significantly decrease aphid populations, and that combining insecticide with Ebf further reduced numbers of apterous aphids at distances of 5 m from pheromone emitters in two years of our experiments. Our results demonstrate that imidacloprid can be effective in reducing the abundance of aphids in Chinese cabbage fields, but the degree of control can be even stronger in the presence of Ebf. [less ▲]

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See detailThe functional significance of E-b-Farnesene: Does it influence the populations of aphid natural enemies in the fields?
Cui, L-L; Francis, Frédéric ULg; Heuskin, Stéphanie ULg et al

in Biological Control (2012)

Aphids cause much damage to Chinese cabbage in northern China. Over reliance on pesticides have large environmental and human health costs that compel researchers to seek alternative management tactics ... [more ▼]

Aphids cause much damage to Chinese cabbage in northern China. Over reliance on pesticides have large environmental and human health costs that compel researchers to seek alternative management tactics for aphid control. The component of aphid alarm pheromone, E-b-Farnesene (EbF), extracted from Matricaria chamomilla L., which attracts natural enemies in the laboratory, may have significant implications for the design of cabbage aphid control strategies. The purpose of this paper is to understand the effects of EbF on natural enemies to cabbage aphid control in Chinese cabbage fields. Ladybeetles on Chinese cabbage leaves in EbF released plots and Aphidiidae in EbF released yellow traps were significantly higher than those of in controls. No significant differences were detected in the interactions of different treatments and the two years for all natural enemies. More important, lower aphid densities were found in EbF released plots. Our results suggested that the EbF extracted from M. chamomilla L. could attract natural enemies to reduce cabbage aphids in the Chinese cabbage fields. [less ▲]

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See detailEquilibrium and metastable phase transitions in silicon nitride at high pressure: A first-principles and experimental study
Xu, Bin ULg; Dong, J.; McMillan, P. F. et al

in Physical Review. B, Condensed Matter and Materials Physics (2011), 84(1),

We have combined first-principles calculations and high-pressure experiments to study pressure-induced phase transitions in silicon nitride (Si 3N 4). Within the quasi-harmonic approximation, we predict ... [more ▼]

We have combined first-principles calculations and high-pressure experiments to study pressure-induced phase transitions in silicon nitride (Si 3N 4). Within the quasi-harmonic approximation, we predict that the α phase is always metastable relative to the β phase over a wide pressure-temperature range. Our lattice vibration calculations indicate that there are two significant and competing phonon-softening mechanisms in the β-Si 3N 4, while phonon softening in the α-Si 3N 4 is rather moderate. When the previously observed equilibrium high-pressure and high-temperature β → γ transition is bypassed at room temperature (RT) due to kinetic reasons, the β phase is predicted to undergo a first-order structural transformation to a denser P6̄ phase above 39 GPa. The estimated enthalpy barrier height is less than 70 meV/atom, which suggests that the transition is kinetically possible around RT. This predicted new high-pressure metastable phase should be classified as a "postphenacite" phase. Our high-pressure x-ray diffraction experiment confirms this predicted RT phase transition around 34 GPa. No similar RT phase transition is predicted for α-Si 3N 4. Furthermore, we discuss the differences in the pressure dependencies of phonon modes among the α, β, and γ phases and the consequences on their thermal properties. We attribute the phonon modes with negative Grüneisen ratios in the α and β phases as the cause of the predicted negative thermal expansion coefficients (TECs) at low temperatures in these two phases, and predict no negative TECs in the γ phase. © 2011 American Physical Society. [less ▲]

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See detailHigh-pressure study of the beta-to-alpha transition in Ga2O3
Machon, D.; McMillan, P. F.; Xu, Bin ULg et al

in Physical Review. B, Condensed Matter and Materials Physics (2006), 73(9),

The high-pressure behavior of Ga2O3 is studied up to 40 GPa using synchrotron x-ray diffraction and Raman spectroscopy in diamond anvil cells. A phase transformation from the monoclinic beta-phase (C2/m ... [more ▼]

The high-pressure behavior of Ga2O3 is studied up to 40 GPa using synchrotron x-ray diffraction and Raman spectroscopy in diamond anvil cells. A phase transformation from the monoclinic beta-phase (C2/m) is observed at a pressure above 20-22 GPa. The high-pressure polymorph is identified as the alpha-phase that is isostructural with corundum (R (3) over barc symmetry) from the x-ray diffraction data. However, considerable anion disorder is indicated by the appearance of broad bands in the Raman spectra. The experimental results are complemented by ab initio theoretical calculations of the energetics of the two structures and the lattice dynamics. [less ▲]

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See detailBlueshifted Raman scattering and its correlation with the [110] growth direction in gallium oxide nanowires
RAO, Rita Flora ULg; Rao, A. M.; Xu, Bin ULg et al

in Journal Of Applied Physics (2005), 98(9),

The Raman spectrum of gallium oxide (beta-Ga2O3) nanowires with [001] growth direction is identical to that of the bulk Ga2O3 [Y. C. Choi Adv. Mater. 12, 746 (2000)] while that of beta-Ga2O3 nanowires ... [more ▼]

The Raman spectrum of gallium oxide (beta-Ga2O3) nanowires with [001] growth direction is identical to that of the bulk Ga2O3 [Y. C. Choi Adv. Mater. 12, 746 (2000)] while that of beta-Ga2O3 nanowires with [40 (1) over bar] growth direction is redshifted by 4-23 cm(-1) [Y. H. Gao Appl. Phys. Lett. 81, 2267 (2002)]. Here we report the Raman and Fourier transform infrared spectra of beta-Ga2O3 nanowires with [110] growth direction which is blueshifted relative to the bulk spectra by similar to 10-40 cm(-1). Based on a first principles calculation of the strain dependence of Raman mode frequencies in bulk beta-Ga2O3, we correlate the observed frequency shifts to growth-direction-induced internal strains in the nanowires. (c) 2005 American Institute of Physics. [less ▲]

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