Search

Cerium (Ce) was effectively transitioned into the high-Mn austenitic steel weld metal under submerged arc welding by adding cerium dioxide and calcium silicon reducing agents into flux. The evolution behaviours of the composition, number density and size of inclusions in weld metal with different Ce contents were systematically investigated by thermodynamic calculation and experiments. The results show that the number density of inclusions increased and average size decreased with the increase of Ce content from 0 to 0.087 wt-%. Meanwhile, and the percentage of inclusions number with size less than 0.80 μm increased from 79.28% to 91.43%. The evolutionary process of inclusions was Al2O3→ Al11O18Ce → CeAlO3→ Ce2O3→ Ce2O2S with the increase of Ce content in the present weld metal. In particular, Ce-O-S-Al inclusion was extracted by in-situsample preparation method, which proved its internal structure and evolution process. The complete formation model of Ce-Al-O-S system was also established.

Cerium (Ce) was effectively transitioned into the high-Mn austenitic steel weld metal under submerged arc welding by adding cerium dioxide and calcium silicon reducing agents into flux. The evolution behaviours of the composition, number density and size of inclusions in weld metal with different Ce contents were systematically investigated by thermodynamic calculation and experiments. The results show that the number density of inclusions increased and average size decreased with the increase of Ce content from 0 to 0.087 wt-%. Meanwhile, and the percentage of inclusions number with size less than 0.80 µm increased from 79.28% to 91.43%. The evolutionary process of inclusions was Al2O3? Al11O18Ce ? CeAlO3? Ce2O3? Ce2O2S with the increase of Ce content in the present weld metal. In particular, Ce-O-S-Al inclusion was extracted by in-situsample preparation method, which proved its internal structure and evolution process. The complete formation model of Ce-Al-O-S system was also established.

We propose and demonstrate a novel concept of Brillouin fiber swept laser with narrow linewidth based on mode following effect. Utilizing the synergy of the Brillouin gain spectrum and cavity mode, the real-time mode following effect is achieved. In the experiment, a tunable laser source was employed to realize synchronous tuning of Brillouin gain spectrum for matching the shift of cavity mode induced by an intra-cavity piezoelectric transducer wound with gain fiber. We theoretically analyzed the influence of the driving parameters and wound fiber length on the frequency sweep range. Experimental results show that the obtained maximum continuous frequency sweep range is ∼445.76 MHz while the driving frequency is 12 kHz and the wound fiber length is 12 m, which is consistent with the theoretical analysis. This new type of fiber swept laser has huge potential application value in optical sensing and communication system.

Ultrafast lasers based on nonlinear polarization rotation has attracted significant attentions, where artificial saturable absorption is induced by Kerr effect. Due to polarization-dependent device within, nonlinear polarization rotation laser cavity generally operates in scalar regime, while vector dynamics have been observed occasionally. However, coherence deterioration induced by nonlinear polarization evolution are rarely reported. Here, we investigate the coherence deterioration for the ultrafast laser systems based on nonlinear polarization rotation. Three types of vector pulses, group velocity locked vector solitons, polarization rotation vector solitons, and coherence deteriorated states can be generated by finely tuning the birefringence of cavity. Combining dispersive Fourier transform and division-of-amplitude facilitates single-shot measurements of wavelength-resolved states of polarization. We find that birefringence-induced phase shift promotes the wavelength-dependent polarization rotation and various polarization evolution speed. In the coherence deteriorated states, optical polarization rogue waves at certain wavelengths are identified, while optical intensities show different irregular probability distributions.

Polarization scramblers are widely employed to mitigate polarization fluctuation-related effects for optical signals propagating in fiber systems. We propose an all-optical polarization scrambler configuration based on a polarization beam splitting delayed fiber loop. By deteriorating the coherence of one beam, and controlling the intensity ratio of two orthogonal beams, the polarization scrambler operates in a chaotic regime. The effect on polarization scrambling of loop structure is tested by a home-made narrow-linewidth laser with linewidth of 500 Hz. We investigate the polarization scrambling performance for a commercial distributed feedback laser with linewidth of 3 MHz in various operating regimes. Scrambling speeds under chaotic regime reach 42 Mrad/s with a degree of polarization <0.1 at the maximum sampling rate of 100 MSa/s. We also characterize the dependence of the scrambling speed and average degree of polarization on delay fiber length and wavelengths within the C-band. The output performance of the proposed scrambler for scrambling 40 MHz and 6 GHz modulated signals are tested and waveform distortions are identified due to polarization scrambling.

Alkaline zinc ion batteries have attracted attention as potential energy storage devices but remain challenging due to the low utilization rate of active substances, poor conductivity, and few active sites. In order to solve these shortcomings, we grow ultrathin nickel-cobalt layered double hydroxides (NiCo LDH) by electrodeposition on Co3O4surfaces, and generated abundant oxygen vacancies in the inner layer of the core-shell structure by electrochemical method. The special core-shell structure improves the contact between the active material and the electrolyte, bringing a positive effect on ion diffusion and charge transfer during the energy storage process. At the same time, the abundant oxygen vacancies not only effectively improve the conductivity and the number of active sites of the material, but also improve the valence state conversion ability of the cobalt element. As expected Co3O4-OV/NiCo LDH exhibits a specific capacity of 338.47 mAh g−1at a current density of 1 A g−1and a high average discharge potential of 1.65 V relative to Zn2+/Zn. Furthermore, the characterizations combined with density functional theory (DFT) calculations indicate that the generation of oxygen vacancies improves the conductivity and the number of active sites which results in excellent reversible electrochemical activity. This work not only provides new insight into designing advanced electrodes by introducing oxygen vacancies but also opens up avenues for the development of high-performance zinc-cobalt batteries.

In the present study, the comprehensive analyses based on the numerical simulation, in situobservation, and metallographic detection were carried out for the roll core of GCr15/45 carbon steel composite roll manufactured by the new electroslag remelting cladding (ESRC) method. During the ESRC process, the temperature distributions at the different radial and longitudinal positions of the roll core have great changes due to the different degrees of heat conduction from the slag bath, as a result, various microstructure and properties were obtained at the different positions of the roll core. The results illustrated that the ESRC process tended to be stable as the composite height reached a certain value and the high-temperature austenitization process mainly occurred in the radial regions where R> 60 mm, whereas no significant changes occurred at the areas where R≦ 60 mm. The coarse grains and few Widmanstatten structures with proeutectoid ferrite were generated in the roll core areas near the bimetallic interface, while the fine grains with more proeutectoid ferrite were obtained in the roll core area away from the interface. Therefore, a higher tensile strength and a better plasticity were obtained for the specimens away from the interface.

ABSTRACTAccording to the previous numerical simulation, a bimetallic composite billet has been produced by the new electroslag cladding method in the present study. Its longitudinal and circumferential macrostructure analyses clearly illustrates that the bonding trend of bimetallic metals changes from slag inclusion defect to good metallurgical bonding with the increasing composite height, which is closely related to the temperature distribution in bimetallic interface. Tensile strength of as-cast sample including the bonding interface can reach 661 MPa with a good plasticity and toughness. In addition, tensile fractures of the as-cast and annealing samples are always located on the roll core side rather than the bimetallic bonding interface which fully prove that the bonding interface is not the weakest area of the composite billet. Based on the above analyses, some useful suggestions about improving the composite billet quality produced by the new electroslag cladding technology have been given.

According to the previous numerical simulation, a bimetallic composite billet has been produced by the new electroslag cladding method in the present study. Its longitudinal and circumferential macrostructure analyses clearly illustrates that the bonding trend of bimetallic metals changes from slag inclusion defect to good metallurgical bonding with the increasing composite height, which is closely related to the temperature distribution in bimetallic interface. Tensile strength of as-cast sample including the bonding interface can reach 661 MPa with a good plasticity and toughness. In addition, tensile fractures of the as-cast and annealing samples are always located on the roll core side rather than the bimetallic bonding interface which fully prove that the bonding interface is not the weakest area of the composite billet. Based on the above analyses, some useful suggestions about improving the composite billet quality produced by the new electroslag cladding technology have been given.

The optical modulation of graphene circumvents the “electrical bottleneck” in electrical field tuning of the Fermi level and motivates diverse graphene-based controllable photonic devices with extraordinary performances. Unfortunately, pervious optical modulation schemes are incoherent, and the Fermi–Dirac distribution formed from a strong pump laser prevents the absorption of a weak probe laser due to the Pauli blocking, making the modulation inconvenient and low in efficiency. Here we demonstrate the coherent optical modulation of graphene based on coherent population oscillation, where ground state population oscillates with a beat frequency equal to the pump and probe frequency difference. To distinguish it from the coexisting incoherent modulation in graphene, a phase-sensitive pump-probe system is constructed with a fiber-based Mach–Zehnder interferometer. Clear resonance within the burning hole of a pump laser is observed in the interference spectrum of a coherent probe laser. The discovery of highly coherent ground state population oscillation in graphene offers new possibilities for manipulating and controlling the phase response of graphene-based photonics with high efficiency.

Ultrafast lasers with tunable capabilities of pulse duration and spectrum have widespread applications in telecommunication, spectroscopy, and nonlinear optical bio-imaging. However, traditional mechanical and electrical tuning methods are still challenging for precise and stable controlling. Based on graphene’s photo-thermal effect, we tune the bandwidths and wavelengths of chirped fiber Bragg gratings with flexible graphene-coating approaches. By inserting the fabricated devices into an ultrafast fiber laser cavity, durations and wavelengths of the generated pulses can be all-optically tuned with sensitivities of 470 fs/mW and 2.9 pm/mW, separately. Such an optical-controlled method provides a compact and precise way to regulate various laser properties.

The microstructure and mechanical properties of the novel cryogenic high-Mn austenitic steel weld metals with different cerium (Ce) contents were investigated via electron back-scattered diffraction, scanning and spherical aberration-corrected transmission electron microscopy, and cryogenic impact and tensile test. The results indicated that the crystallographic grain size was significantly refined, and the relative frequency of high-angle grain boundaries increased with the increase of Ce content. Ce element addition could modify the main inclusions from irregular Al2O3into regular Ce-containing inclusions. Meanwhile, the inclusions gradually became fine and dispersed, and the volume fraction of inclusions decreased with the increase of Ce content from 0 to 870 ppm. The increase of Ce content continuously improved cryogenic impact toughness from 82 J to 116 J, and yield strength, tensile strength and total elongation all increased to different degrees. We found that in addition to the beneficial changes in inclusion modification, grain refinement and increase in the proportion of high-angle grain boundaries, the solid solution of Ce also played a crucial role in the mechanical properties.

An automatic understanding system MAD-READER based on the techniques of image processing, pattern recognition, and artificial intelligence has been developed for mechanical engineering drawings. The principles of the system are presented, which include the methods and techniques of recognition and understanding for topological assembly drawings (TAD). A rule-based generator GEN-PLAN is devised to generate directly assembly plans from TAD assembly drawings. A variety of TAD assembly drawings has been used for testing the generator. So far, GEN-PLAN has been used to recognize TAD assembly drawings which consist of 31 part symbols, and generate their assembly plans. The present generator has shown favorable results.

We demonstrate the experimental observation of bound states (BSs) of Q-switched lasers mode-locked by carbon nanotubes. When BSs of Q-switched mode-locked lasers are formed, small temporal interval results into multiwavelength spectrum due to the Fourier transformation. We find that the wavelength spacing is highly sensitive to pump power. A wavelength spacing tuning from ?0.057 to 1.569 nm with a pump power variation less than 4 mW is obtained. The wavelength spacing is also highly sensitive to the nonlinear phase induced by polarization controller. These findings enrich our understanding about the complex dynamics of the Q-switched mode-locked lasers.

We demonstrate novel polarization-dependent pulse dynamics in a fiber laser cavity mode-locked by single-wall carbon nanotubes. By managing the net dispersion and polarization state, we obtain two noise-like pulsing procedures with distinctive polarization characteristics. Ultrafast polarization measurements reveal double pulses are produced by the combined effects of double-scroll chaotic polarization attractors and the polarization mode dispersion of single-mode fiber. The corresponding single-shot spectra provide evidence of coherent energy coupling between pulses during the switching process, due to the polarization hole burning of the active medium. The relative results provide new information for the polarization control of ultrafast lasers.

We demonstrate the evolution characteristics of laser linewidth in accordance to Rayleigh backscattering (RBS) signal accumulated from different lengths of the RBS fiber. An ultra-narrow-linewidth fiber laser operating in single longitudinal mode has been obtained. The output linewidth is approximately 210 Hz and the side-mode suppression ratio is as high as ?60 dB provided the length of the RBS fiber is set to be 5 km. The theoretical prediction suggests linewidth of tens of Hertz could be achieved provided the experimental setup is further optimized and the temperature control device is introduced.