Influence of lunar regolith compressibility on sampling performance of thick wall spiral drills

A 2 m class robotic drill was sent to the Moon and successfully collected and returned regolith samples in late 2020 by China.It was a typical thick wall spiral drill(TWSD)with a hollow auger containing a complex coring system to retain subsurface regolith samples.Before the robotic drill was launched,a series of laboratory tests were carried out to investigate and predict the possible drilling loads it may encounter in the lunar environment.This work presents how the sampling performance of the TWSD is affected by the regolith compressibility.Experiments and analysis during the drilling and sampling process in a simulated lunar regolith environment were conducted.The compressibility of a typical lunar regolith simulant(LRS)was measured through unidirectional compression tests to study the relationship between its inner regolith stress and bulk density.A theoretical model was established to elucidate the cutting discharge behavior by auger flights based on the aforementioned relationship.Experiments were conducted with the LRS,and the results show that the sampling performance is greatly affected by the flux of the drilled cuttings into the spiral flight channels.This work helped in scheduling reasonable drilling parameters to promote the sampling performance of the robotic drill in the Chinese Chang’E 5 mission.

Research on the sampling performance of a new bionic gravity sampler

Gravity sampling is of vital importance for sampling seabed sediments and understanding submarine sedimentary environments and resources.In this study,a new bionic sampler tube(BST)with non-smooth surface for low-disturbance and rapid sampling is presented.The BST with depressions and swellings on its surface was designed on the model of the non-smooth surface of the dung beetle.Sufficient theoretical calculations,numerical simulations,and experimental tests were carried out to study its sampling performance.The penetration depth,sample length,and frictional drag of the sampler tube were calculated.The finite element model and the coupled Eulerian-Lagrangian(CEL)method were used to analyze and compare its sampling performance.Laboratory and field gravity sampling tests were conducted and the results demonstrated the advantages of the BST in improving sampling performance and in reducing adhesion and drag.

Design and experimental validation of improved grapevine burying machine

In order to address the low soil breaking rate,poor soil covering performance,and low working efficiency of the existing 3MT-1.8 and PMT-75 grapevine burying machines,two types of improved burying machines,namely the 3MTLJ-1.8 and 3MTXP-1.8,were developed in consideration of the local Ningxia soil conditions.Field experimental results indicated that the soil breaking rate of the 3MTLJ-1.8 machine was 71.44%,and its soil sampling volume increased by approximately 30%compared to that of the 3MT-1.8 machine.It was verified that the self-developed 3MTLJ-1.8 machine can be used in the southern regions of Ningxia.Furthermore,the soil sampling volume of the 3MTXP-1.8 burying machine was 0.24 m^(3)/m,and its soil breaking rate increased by more than 41.42%compared to the standard required volume.The 3MTXP-1.8 machine can be used in the northern areas of Ningxia,where the soil hardness is higher.The results can provide a reference for the development and popularization of grapevine burying machines in Ningxia.

Analysis of trace dicyandiamide in stream water using solid phase extraction and liquid chromatography UV spectrometry

An improved method for trace level quantification of dicyandiamide in stream water has been developed. This method includes sample pretreatment using solid phase extraction.The extraction procedure（including loading, washing, and eluting） used a flow rate of1.0 m L/min, and dicyandiamide was eluted with 20 m L of a methanol/acetonitrile mixture（V/V = 2：3）, followed by pre-concentration using nitrogen evaporation and analysis with high performance liquid chromatography–ultraviolet spectroscopy（HPLC–UV）. Sample extraction was carried out using a Waters Sep-Pak AC-2 Cartridge（with activated carbon）.Separation was achieved on a ZIC-Hydrophilic Interaction Liquid Chromatography（ZIC-HILIC）（50 mm × 2.1 mm, 3.5 μm） chromatography column and quantification was accomplished based on UV absorbance. A reliable linear relationship was obtained for the calibration curve using standard solutions（R^2〉 0.999）. Recoveries for dicyandiamide ranged from 84.6% to 96.8%, and the relative standard deviations（RSDs, n = 3） were below 6.1% with a detection limit of 5.0 ng/m L for stream water samples.

Estimation of Censored Regression Model： A Simulation Study

We investigate the finite sample performance of several estimators proposed for the panel data Tobit regression model with individual effects, including Honor6 estimator, Hansen＇s best two-step GMM estimator, the continuously updating GMM estimator, and the empirical likelihood estimator （ELE）. The latter three estimators are based on more conditional moment restrictions than the Honor6 estimator, and consequently are more efficient in large samples. Although the latter three estimators are asymptotically equivalent, the last two have better finite sample performance. However, our simulation reveals that the continuously updating GMM estimator performs no better, and in most cases is worse than Honor6 estimator in small samples. The reason for this finding is that the latter three estimators are based on more moment restrictions that require discarding observations. In our designs, about seventy percent of observations are discarded. The insufficiently few number of observations leads to an imprecise weighted matrix estimate, which in turn leads to unreliable estimates. This study calls for an alternative estimation method that does not rely on trimming for finite sample panel data censored regression model.