查看更多>>摘要：Dissipative soliton resonance(DSR)was previously studied in separated mode-locked fiber lasers within different dispersion regimes including anomalous,near-zero and normal dispersion.Here we propose a method to study DSR in a single mode-locked laser in these different dispersion regimes.This is achieved by virtue of a waveshaper which can control the laser dispersion readily using software,avoiding the usual tedious cutback method.We find that dispersion has a negligible effect on DSR since the pulse duration keeps constant while dispersion is varied.Moreover,we examine the dynamics of DSR on the parameters of the SA including modulation depth and saturation power,and find that the pulse duration can be changed in a large range when the saturation power is decreased.Our numerical simulations could be important to guide relative experimental studies.
查看更多>>摘要：A wavelength-interval switchable Brillouin-Raman random fiber laser(BRRFL)based on Brillouin pump(BP)ma-nipulation is proposed in this paper.The proposed wavelength-interval switchable BRRFL has a full-open cavity configu-ration,featuring multi wavelength output with wavelength interval of double Brillouin frequency shifts.Through simulta-neously injecting the BP light and its first-order stimulated Brillouin-scattered light into the cavity,the laser output exhibits a wavelength interval of single Brillouin frequency shift.The wavelength-interval switching effect can be manipulated by controlling the power of the first-order stimulated Brillouin scattering light.The experimental results show the multiwave-length output can be switched between double Brillouin frequency shift multiwavelength emission with a broad bandwidth of approximately 60 nm and single Brillouin frequency shift multiwavelength emission of 44 nm.The flexible optically controlled random fiber laser with switchable wavelength interval makes it useful for a wide range of applications and holds significant potential in the field of wavelength-division multiplexing optical communication.
查看更多>>摘要：Chalcogenide superlattices Sb2Te3-GeTe is a candidate for interfacial phase-change memory(iPCM)data storage devices.By employing terahertz emission spectroscopy and the transient reflectance spectroscopy together,we investigate the ultrafast photoexcited carrier dynamics and current transients in Sb2Te3-GeTe superlattices.Sample orientation and excitation polarization dependences of the THz emission confirm that ultrafast thermo-electric,shift and injection currents contribute to the THz generation in Sb2Te3-GeTe superlattices.By decreasing the thickness and increasing the number of GeTe and Sb2Te3 layer,the interlayer coupling can be enhanced,which significantly reduces the contribution from circular photo-galvanic effect(CPGE).A photo-induced bleaching in the transient reflectance spectroscopy probed in the range of～1100 nm to～1400 nm further demonstrates a gapped state resulting from the interlayer coupling.These demonstrates play an important role in the development of iPCM-based high-speed optoelectronic devices.
查看更多>>摘要：Thickness measurement plays an important role in the monitoring of pipeline corrosion damage.However,the require-ment for prior knowledge of the shear wave velocity in the pipeline material for popular ultrasonic thickness measurement limits its widespread application.This paper proposes a method that utilizes cylindrical shear horizontal(SH)guided waves to estimate pipeline thickness without prior knowledge of shear wave velocity.The inversion formulas are derived from the dispersion of higher-order modes with the high-frequency approximation.The waveform of the example problems is simulated using the real-axis integral method.The data points on the dispersion curves are processed in the frequency domain using the wave-number method.These extracted data are then substituted into the derived formulas.The results verify that employing higher-order SH guided waves for the evaluation of thickness and shear wave velocity yields less than 1％error.This method can be applied to both metallic and non-metallic pipelines,thus opening new possibilities for health monitoring of pipeline structures.
查看更多>>摘要：Strengthened directivity with higher-order side lobes can be generated by the transducer with a larger radius at a higher frequency.The multi-annular pressure distributions are displayed in the cross-section of the acoustic vortices(AVs)which are formed by side lobes.In the near field,particles can be trapped in the valley region between the two annuli of the pressure peak,and cannot be moved to the vortex center.In this paper,a trapping method based on a sector transducer array is proposed,which is characterized by the continuously variable topological charge(CVTC).This acoustic field can not only enlarge the range of particle trapping but also improve the aggregation degree of the trapped particles.In the experiments,polyethylene particles with a diameter of 0.2 mm are trapped into the multi-annular valleys by the AV with a fixed topological charge.Nevertheless,by applying the CVTC,particles outside the radius of the AV can cross the pressure peak successfully and move to the vortex center.Theoretical studies are also verified by the experimental particles trapping using the AV with the continuous variation of three topological charges,and suggest the potential application of large-scale particle trapping in biomedical engineering.
查看更多>>摘要：The experimental research on zero-net-mass-flux jet closed-loop active control was conducted in the wind tunnel.The mu-level method successfully detected burst events of the coherent structures.The streamwise velocity signals in the turbulent boundary layer were measured by HWA.The drag reduction rate of 16.7％is obtained comparable to that of the open-loop control and saves 75％of the input energy at the asynchronous 100 V/160 Hz control case,which reflects the advantages of the closed-loop control.The experimental findings indicate that the intensity increases in the near-wall region.The perturbation of the PZT vibrators on the skewness factor is concentrated in the region y+＜60.The generation of high-speed fluids is depressed and the downward effect of high-speed fluids weakens.The alteration of energy distribution and the discernible impact of modulation between structures of varying scales are observed.The correlation coefficient exhibits a strong positive correlation,which indicates that the large-scale structures produce modulation effect on small-scale ones.The occurrence of burst events is effectively suppressed.The disturbance has the characteristics of stable periodicity,positive and negative symmetry,low intermittency,and high pulsation strength.The conditional phase waveform shows that the fluctuation amplitude increases,indicating amplitude modulation effects on coherent structures.
查看更多>>摘要：We study the effect of particle size polydispersity(δ)on the melting transition(T*),local ordering,solid-liquid coexistence phase and dynamics of two-dimensional Lennard-Jones fluids up to moderate polydispersity by means of computer simulations.The particle sizes are drawn at random from the Gaussian(G)and uniform(U)distribution functions.For these systems,we further consider two different kinds of particles,viz.,particles having the same mass irrespective of size,and in the other case the mass of the particle scales with its size.It is observed that with increasing polydispersity,the value of T*initially increases due to improved packing efficiency(φ)followed by a decrease and terminates at δ ≈8％(U-system)and 14％(G-system)with no significant difference for both mass types.The interesting observation is that the particular value at which φ drops suddenly coincides with the peak of the heat capacity(Cp)curve,indicating a transition.The quantification of local particle ordering through the hexatic order parameter(Q6),Voronoi construction and pair correlation function reveals that the ordering decreases with increasing δ and T.Furthermore,the solid-liquid coexistence region for the G-system is shown to be comparatively wider in the T-δ plane phase diagram than that for the U system.Finally,the study of dynamics reveals that polydisperse systems relax faster compared to monodisperse systems;however,no significant qualitative differences,depending on the distribution type and mass polydispersity,are observed.
查看更多>>摘要：Due to a series of challenges such as low-orbit maintenance of satellites,the air-breathing electric propulsion has got widespread attention.Commonly,the radio frequency ion thruster is favored by low-orbit missions due to its high specific impulse and efficiency.In this paper,the power transfer efficiency of the radio frequency ion thruster with different gas compositions is studied experimentally,which is obtained by measuring the radio frequency power and current of the antenna coil with and without discharge operation.The results show that increasing the turns of antenna coils can effectively improve the radio frequency power transfer efficiency,which is due to the improvement of Q factor.In pure N2 discharge,with the increase of radio frequency power,the radio frequency power transfer efficiency first rises rapidly and then exhibits a less steep increasing trend.The radio frequency power transfer efficiency increases with the increase of gas pressure at relatively high power,while declines rapidly at relatively low power.In N2/O2 discharge,increasing the N2 content at high power can improve the radio frequency power transfer efficiency,but the opposite was observed at low power.In order to give a better understanding of these trends,an analytic solution in limit cases is utilized,and a Langmuir probe was employed to measure the electron density.It is found that the evolution of radio frequency power transfer efficiency can be well explained by the variation of plasma resistance,which is related to the electron density and the effective electron collision frequency.
查看更多>>摘要：The atomic structure of amorphous alloys plays a crucial role in determining both their glass-forming ability and magnetic properties.In this study,we investigate the influence of adding the Y element on the glass-forming ability and magnetic properties of Fe86-xYxB7C7(x=0,5,10 at.％)amorphous alloys via both experiments and ab initio molecular dynamics simulations.Furthermore,we explore the correlation between local atomic structures and properties.Our results demonstrate that an increased Y content in the alloys leads to a higher proportion of icosahedral clusters,which can po-tentially enhance both glass-forming ability and thermal stability.These findings have been experimentally validated.The analysis of the electron energy density and magnetic moment of the alloy reveals that the addition of Y leads to hybridization between Y-4d and Fe-3d orbitals,resulting in a reduction in ferromagnetic coupling between Fe atoms.This subsequently reduces the magnetic moment of Fe atoms as well as the total magnetic moment of the system,which is consistent with experimental results.The results could help understand the relationship between atomic structure and magnetic property,and providing valuable insights for enhancing the performance of metallic glasses in industrial applications.
查看更多>>摘要：Mn3TeO6(MTO)has been experimentally found to adopt a P21/n structure under high pressure,which exhibits a significantly smaller band gap compared to the atmospheric R(3)phase.In this study,we systematically investigate the magnetism,structural phase transition,and electronic properties of MTO under high pressure through first-principles cal-culations.Both R(3)and P21/n phases of MTO are antiferromagnetic at zero temperature.The R(3)phase transforms to the P21/n phase at 7.58 GPa,accompanied by a considerable volume collapse of about 6.47％.Employing the accurate method that combines DFT+U and GW,the calculated band gap of R3 phase at zero pressure is very close to the experimental values,while that of the P21/n phase is significantly overestimated.The main reason for this difference is that the experi-mental study incorrectly used the Kubelka-Munk plot for the indirect band gap to obtain the band gap of the P21/n phase instead of the Kubelka-Munk plot for the direct band gap.Furthermore,our study reveals that the transition from the R(3)phase to the P21/n phase is accompanied by a slight reduction in the band gap.
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