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Au nanoparticles (Au NPs) have attracted much interest owing to their unique optical properties. In this paper, a facile process has been successfully developed to synthesize the SiO2/Au hybrid microspheres with a diameter of 200 nm via the galvanic replacement of SiO2/Ag hybrid microspheres and chlorauric acid (HAuCl4) solution. The as-prepared products were investigated by x-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM, JEOL-6700F), and transmission electron microscopy (TEM, JEOL 3010), respectively. As expected, the as-prepared SiO2/Au hybrid microspheres show strong chemical stability and superior catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). The SiO2/Au hybrid microspheres would be found widely used in wastewater treatment, catalytic reaction, bacteriostatic and bactericidal applications.
The high repetition rate 10 J/10 ns Yb:YAG laser system and its key techniques are reported. The amplifiers in this system have a multi-pass V-shape structure and the heat in the amplifiers is removed by means of laminar water flow. In the main amplifier, the laser is four-pass, and an approximately 8.5 J/1 Hz/10 ns output is achieved in the primary test. The far-field of the output beam is approximately 10 times the diffraction limit. Because of the higher levels of amplified spontaneous emission (ASE) in the main amplifier, the output energy is lower than expected. At the end we discuss some measures that can improve the properties of the laser system.
It is demonstrated by simulations and analysis that a wakefield driven by an ultrashort intense laser pulse in underdense plasma can emit tunable electromagnetic radiation along the laser propagation direction. The profile of such a kind of radiation is closely associated with the structure of the laser wakefield. In general, electromagnetic radiation in the terahertz range with its frequency a few times the electron plasma frequency can be generated in the moderate intensity regime. In the highly nonlinear case, a chain of radiation pulses is formed corresponding to the nonlinear structure of the wake. Study shows that the radiation is associated with the self-modulation process of the laser pulse in the wakefield and resulting transverse electron momenta from modulated asymmetric laser fields.
It is found that there is an upper-limit critical power for self-guided propagation of intense lasers in plasma in addition to the well-known lower-limit critical power set by the relativistic effect. Above this upper-limit critical power, the laser pulse experiences defocusing due to expulsion of local plasma electrons by the transverse ponderomotive force. Associated with the upper-limit power, a lower-limit critical plasma density is also found for a given laser spot size, below which self-focusing does not occur for any laser power. Both the upper-limit power and the lower-limit density are derived theoretically and verified by two-dimensional particle-in-cell simulations. The present study provides new guidance for experimental designs, where self-guided propagation of lasers is essential.
A double-slice-foil target is proposed for the generation of quasi-monoenergetic proton bunches by intense laser pulses. In this new target structure, two symmetrical solid slices are adjoined obliquely to the front side of a plane double-layer target. Two-dimensional particle-in-cell simulations show that a large number of hot electrons are pulled out from solid slices and accelerated forward by direct laser acceleration, which lead to significant enhancement of the sheath field and the produced proton beam energy as compared with the normal plane double-layer target and some other modified targets. It appears that well-collimated proton bunches with energy larger than 200 MeV can be produced at the focused laser intensity of about 1021W/cm2 with the proposed target design.
Energetic electron beam generation from a thin foil target by the ponderomotive force of an ultra-intense circularly polarized laser pulse is investigated. Two-dimensional particle-in-cell (PIC) simulations show that laser pulses with intensity of 1022–1023 Wcm−2 generate about 1–10 GeV electron beams, in agreement with the prediction of one-dimensional theory. When the laser intensity is at 1024–1025 Wcm−2, the beam energy obtained from PIC simulations is lower than the values predicted by the theory. The radiation damping effect is considered, which is found to become important for the laser intensity higher than 1025 Wcm−2. The effect of laser focus positions is also discussed.
A review is presented on our recent Vlasov-Fokker-Planck (VFP) simulation code development and applications for high-power laser-plasma interactions. Numerical schemes are described for solving the kinetic VFP equation with both electron-electron and electron-ion collisions in one-spatial and two-velocity (1D2V) coordinates. They are based on the positive and flux conservation method and the finite volume method, and these two methods can insure the particle number conservation. Our simulation code can deal with problems in high-power laser/beam-plasma interactions, where highly non-Maxwellian electron distribution functions usually develop and the widely-used perturbation theories with the weak anisotropy assumption of the electron distribution function are no longer in point. We present some new results on three typical problems: firstly the plasma current generation in strong direct current electric fields beyond Spitzer-Härm’s transport theory, secondly the inverse bremsstrahlung absorption at high laser intensity beyond Langdon’s theory, and thirdly the heat transport with steep temperature and/or density gradients in laser-produced plasma. Finally, numerical parameters, performance, the particle number conservation, and the energy conservation in these simulations are provided.
Ionization-induced injection into a laser-driven wakefield is studied using 2½D OSIRIS simulations. A laser propagates into a gas mixture of 99.5% helium and 0.5% nitrogen with gas density of each rising linearly from 0 to a peak, after which these remain constant. Simulations show that the process can be controlled by varying the scale length of an up-ramp, the laser intensity, and the maximum plasma density. The injection process is controlled by the bubble radius decreasing as laser propagates up the density gradient and laser self-focusing in the flat-top region. A beam with a central energy of 350 MeV and an energy spread (FWHM) of 1.62% was obtained for an up-ramp length of 135 μm, a normalized vector potential of 2, and a density of 7 × 1018cm−3 (assuming a 0.8 μm wavelength laser).
We have demonstrated and studied polymeric solid-state dye lasers (SSDLs) fabricated by three-dimensional (3D) polystyrene colloidal crystals and tert-butyl roadamine B (t-Bu RhB) doped Poly (methyl methacrylate) (PMMA) films with different film thickness. The sandwich-typed resonator cavities with different active layer thickness display single-mode lasing oscillations in the reflection bandgap of the colloidal crystals. The lasing thresholds could be optimized by changing the thickness of t-Bu RhB doped PMMA films, which is as low as 7.43 W/cm2. Adjusting active layer thickness would provide an opportunity to accelerate the development of fabricating polymeric SSDLs with low threshold.
The outcome of Plasmodium yoelii 17XL-infected BALB/c and DBA/2 mice, ranging from death to spontaneous cure, respectively, depends largely on the establishment of effective pro-inflammatory type 1 responses during the early stages of infection and associates with CD4+CD25+Foxp3+regulatory T cells (Tregs). Here, effects of Tregs were analysed on early P. yoelii 17XL infection in BALB/c and DBA/2 mice. In vivo depletion of Tregs significantly reversed the inhibited establishment of effective pro-inflammatory type 1 responses in BALB/c mice, indicating that this cell population contributed to the suppression of T-cell function in malaria. Moreover, the proportion and absolute numbers of IL-10-secreting Tregs in BALB/c mice were significantly higher than that found in DBA/2 mice by intracytoplasmic staining, and IL-10 production was correlated with the Tregs population. In addition, in vivo Tregs depletion decreased the production of IL-10 and the apoptosis of CD4+ T cells. Consistently, IL-10R blockade also had the same effect as that of Tregs depletion in P. yoelii 17XL-infected BALB/c mice. Our data demonstrate that Tregs perhaps have an important role in regulating pro-inflammatory type 1 responses in an IL-10-dependent manner and induce CD4+ T cell apoptosis during the early stage of P. yoelii 17XL infection.
Duck interleukin (IL)-18 mature protein gene was amplified by reverse transcription-polymerase chain reaction (RT-PCR) from total RNA extracted from Ma duck (Tadorna ferruginea) splenocytes. The PCR product was cloned into pGEM-T Easy vector for sequencing. The result revealed that the nucleotide sequence of duck IL-18 mature protein gene (mDuIL-18) consisted of a 513 bp band. A prokaryotic plasmid of mDuIL-18, pQE30-mDuIL18, was obtained by subcloning the encoding region of the DuIL-18 mature peptide into pQE30. pQE30-mDuIL18 transformed Escherichia coli M15. The expression of mDuIL-18 gene was identified by SDS-PAGE and Western blotting. Its molecular weight was 19.76 kDa, and could be specifically recognized by rabbit sera to chicken IL-18. The expressed products existed as inclusion bodies. After being degenerated, then renatured, the activities of the inclusion bodies were detected by methyl thiazolyl tetrazolium (MTT) assay. In ducks injected intramuscularly with mDuIL-18 protein (150 ng or 200 ng per duck) and Avian influenza virus (AIV) vaccine 2 weeks after immunization, the average titres of haemagglutination inhibition (HI) antibodies to AIV reached 7.5–7.7 log2, while those of HI antibody ranged between 6.3 and 6.6 log2 in ducks vaccinated with AIV vaccine only or with 100 ng mDuIL-18 and AIV vaccine. The results clearly showed that 150 ng mDuIL-18 per duck strengthened the in vivo immune responses induced by the inactivated oil emulsion AIV vaccine.
In the two-dimensional simulation of the interaction of an ultrashort intense laser with droplet plasma, two hot electron jets generated by resonance absorption and emitted symmetrically with respect to the laser propagation direction are observed at a low laser field amplitude such as $a_0=0.1$. However, the emission angle of electron jets cannot be explained simply with the theory of resonance absorption for planar targets. When the laser amplitude is increased to $a_0=2$, electron bunches generated by the ponderomotive force separated by a laser period are superimposed into the hot electron jets. Accelerated ions have two groups at low laser intensities, one is anisotropic and associated with hot electron jets and the other is isotropic due to hydrodynamics expansion. At high light intensities, isotropic ion acceleration is found through Coulomb explosion.
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