TBM Disc Cutter Model Based on Admissible Energy Principles

Disc cutters are the most critical tool for excavation by tunnel boring machine(TBM). Based on the energy conservation law, finite-element modeling, and elastic–plastic continuum theory for tunneling by TBM, the interaction between disc cutters and rock mass was examined. First, the disc cutter motion was studied to establish the disc cutter strain equations as a function oftime. Second, by using elastic–plastic theory, a rock strain model was constructed. Finally, a three-directional force model with time-varying characteristics was established for disc cutters during rock breaking. The model was applied to the Qinling Mountains Tunnel of the Lan-Yu Railway. Model cutterhead thrust and torque values were found in good agreement with actual data. In brief, the model can be used to predict the TBM performance and examine the mechanism ofrock breaking.

Phase Compensation of Composite Material Radomes Based on the Radiation Pattern

Some compensation methods have been pro- posed to mitigate the degradation of radiation characteris- tics caused by composite material radomes, however most of them are complex and not applicable for large radomes, for example, the modification of geometric shape by grinding process. A novel and simple compensation strat- egy based on phase modification is proposed for large reflector antenna-radome systems. Through moving the feed or sub-reflector along axial direction opportunely, the modification of phase distribution in the original aperture of an enclosed reflector antenna can be used to reduce the phase shift caused by composite material radomes. The distortion of far-field pattern can be minimized. The modification formulas are proposed, and the limitation of their application is also discussed. Numerical simulations for a one-piece composite materials sandwich radome and a 40 m multipartite composite materials sandwich radome verify that the novel compensation strategy achieves sat- isfactory compensated results, and improves the distortion of the far-field pattern for the composite material radomes. For one-piece dielectric radome, more than 60% phasedifference caused by radome is reduced. For multipartite radome, the sidelobe level improves about 1.2 dB, the nulling depth improves about 3 dB. The improvement of far-field pattern could be obtained effectively and simply by moving the feed or sub-reflector according to phase shift of the radome.

Effect of Surface Roughness in Micro-nano Scale on Slotted Waveguide Arrays in Ku-band

Modeling of the roughness in micro-nano scale and its influence have not been fully investigated, however the roughness will cause amplitude and phase errors of the radiating slot, and decrease the precision and efficiency of the SWA in Ku-band. Firstly, the roughness is simulated using the electromechanical coupled（EC） model. The relationship between roughness and the antenna＇s radiation properties is obtained. For verification, an antenna proto- type is manufactured and tested, and the simulation method is introduced. According to the prototype, a contrasting experiment dealing with the flatness of the radiating plane is conducted to test the simulation method. The advantage of the EC model is validated by comparisons of the EC model and two classical roughness models （sine wave and fractal function）, which shows that the EC model gives a more accurate description model for roughness, the maxi- mum error is 13%. The existence of roughness strongly broadens the beamwidth and raises the side-lobe level of SWA, which is 1.2 times greater than the ideal antenna. In addition, effect of the EC model＇s evaluation indices is investigated, the most affected scale of the roughness is found, which is 1/10 of the working wavelength. The proposed research provides the instruction for antenna designing and manufacturing.

Timing fluctuation correction for the front end of a 100-PW laser

The development of high-intensity ultrafast laser facilities provides the possibility to create novel physical phenomena and matter states.The timing fluctuation of the laser pulses is crucial for pump–probe experiments,which is one of the vital means to observe the ultrafast dynamics driven by intense laser pulses.In this paper,we demonstrate the timing fluctuation characterization and control of the front end of a 100-PW laser that is composed of a high-contrast optical parametric amplifier(seed)and a 200-TW optical parametric chirped pulse amplifier(preamplifier).By combining the timing jitter measurement with a feedback system,the laser seed and preamplifier are synchronized to the reference with timing fluctuations of 1.82 and 4.48 fs,respectively.The timing system will be a key prerequisite for the stable operation of 100-PW laser facilities and provide the basis for potential pump–probe experiments performed on the laser.

Seismic anisotropy and upper mantle dynamics in Alaska:A review of shear wave splitting analyses

Shear wave splitting(SWS)is regarded as the most effective geophysical method to delineate mantle flow fields by detecting seismic azimuthal anisotropy in the earth's upper mantle,especially in tectonically active regions such as subduction zones.The Aleutian-Alaska subduction zone has a convergence rate of approximately 50 mm/yr,with a trench length reaching nearly 2800 km.Such a long subduction zone has led to intensive continental deformation and numerous strong earthquakes in southern and central Alaska,while northern Alaska is relatively inactive.The sharp contrast makes Alaska a favorable locale to investigate the impact of subduction on mantle dynamics.Moreover,the uniqueness of this subduction zone,including the unusual subducting type,varying slab geometry,and atypical magmatic activity and composition,has intrigued the curiosity of many geoscientists.To identify different sources of seismic anisotropy beneath the Alaska region and probe the influence of a geometrically varying subducting slab on mantle dynamics,extensive SWS analyses have been conducted in the past decades.However,the insufficient station and azimuthal coverage,especially in early studies,not only led to some conflicting results but also strongly limited the in-depth investigation of layered anisotropy and the estimation of anisotropy depth.With the completion of the Transportable Array project in Alaska,recent studies have revealed more detailed mantle structures and characteristics based on the dense station coverage and newly collected massive seismic data.In this study,we review significant regional-and continental-scale SWS studies in the Alaska region and conclude the mantle flow fields therein,to understand how a geometrically varying subducting slab alters the regional mantle dynamics.The summarized mantle flow mechanisms are believed to be conducive to the understanding of seismic anisotropy patterns in other subduction zones with a complicated tectonic setting.

The microstructure and magnetization reversal behavior of melt-spun (Nd_(1-x)Ce_x)-Fe-B ribbons

In this study, the alloy ingots with nominal compositions of （Nd1_xCex）31FebalCoo.2Gao.1B （x = 0, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%） were prepared and then melt-spun to form nanocrystalline ribbons at the wheel speed of 20 m/s. XRD results show that all melt-spun ribbons exhibit the tetragonal structure （Nd,Ce）2Fe14B phase with the space group P42]rnmm. The Curie temperature and lattice constant decrease with the increase of Ce content. The Curie temperature decreases gradually from 306 to 247 ~C with the increase of Ce content. Those results indicate that Ce element has been incorporated into Nd2Fe14B main crystalline phase and formed （Ce,Nd）-Fe-B hard magnetic phase. It is also found that the remanence ratio （Mr/Ms） decreases from 0.693 to 0.663 and the coercivity （Hc） decreases from 18.7 to 14.2 kOe with the increase of Ce content. However, a relatively high coercivity of 18.3 kOe for （Ndl xCex）31FebalCoo.2Gao.lB （x = 0.2） melt-spun ribbon is achieved. The coercivity is sensitive to microstructure. The AFM patterns show the sample （x - 0.2） has the most uniform and finest micro- structure. The magnetization reversal behavior （0M plots） is discussed in detail. The positive 0M value is observed in every sample, which confirms the existence of exchange coupling interaction. Evidently, the OM maximum value reaches 0.9 in the sample （x - 0.2）. It is indicated that the intergranular exchange coupling effect is the strongest, which is consistent with coercivity enhancing.