A series
of novel steroidal derivatives with a substituted 1,3,4-oxadiazole
structure was designed and synthesized, and the target compounds were
evaluated for their insecticidal activity against five aphid species.
Most of the tested compounds exhibited potent insecticidal activity
against Eriosoma lanigerum (Hausmann), Myzus persicae, and Aphis citricola. Compounds 20g and 24g displayed the highest
activity against E. lanigerum, showing
LC50 values of 27.6 and 30.4 μg/mL, respectively.
Ultrastructural changes in the midgut cells of E. lanigerum were detected by transmission electron microscopy, indicating that
these steroidal oxazole derivatives might exert their insecticidal
activity by destroying the mitochondria and nuclear membranes in insect
midgut cells. Furthermore, a field trial showed that compound 20g exhibited effects similar to those of the positive controls
chlorpyrifos and thiamethoxam against E. lanigerum, reaching a control rate of 89.5% at a dose of 200 μg/mL after
21 days. We also investigated the hydrolysis and metabolism of the
target compounds in E. lanigerum by
assaying the activities of three insecticide-detoxifying enzymes.
Compound 20g at 50 μg/mL exhibited inhibitory action
on carboxylesterase similar to the known inhibitor triphenyl phosphate.
The above results demonstrate the potential of these steroidal oxazole
derivatives to be developed as novel pesticides.
A widely tunable single-longitudinal-mode (SLM) ytterbium-doped fiber laser is experimentally demonstrated, which is achieved by combining a fiber Lyot filter and a saturable absorber in a ring cavity. Stable SLM operation from 1045 nm to 1076 nm is obtained by properly adjusting the polarization state. The output power reaches 7.5 dBm with a fluctuation of less than 2 dB. The optical signal-to-noise ratio is 42.5 dB with a fluctuation of less than 6 dB in this wavelength range.
A mid-infrared fiber optical parametric oscillator is proposed and designed based on a three-hole As(2)S(5) suspended-core fiber (SCF). The eigenmodes of the SCF are depicted and the pump condition for single-mode operation is analyzed. The zero-dispersion wavelength is shifted to 2 μm by tuning the core diameter of the SCF. Using the degenerate four-wave mixing coupled-wave equations, a tuning range of the idler wavelength from 2 to 5 μm and a maximum conversion efficiency of 19% are numerically predicted in a 0.1-m-long SCF pumped by a 2.7 W thulium-doped fiber laser.
Abstract.A three-hole As2S5 suspended-core fiber with a zero-dispersion wavelength of 2 μm is proposed to construct a mid-infrared (MIR) fiber optical parametric oscillator (FOPO). The numerical model of the MIR FOPO is established and a tuning range from 2 to 5 μm for the idler light is predicted.
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