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In the process of registering point clouds with low feature recognition, traditional methods based on local feature extraction and matching are usually not accurate, while the accuracy and efficiency of methods based on global feature matching are also hard to guarantee. In response to this problem, this paper proposed an improved local feature matching method. In initial registration, it designed a key point extraction method based on normal vector projection covariance analysis. Then it used fast point feature histogram( FPFH) descriptor to characterize these key points,and defined multiple matching conditions to screen the feature points. Finally, it took the sum of the nearest distance of the corresponding points as the optimization goal for rough matching. In fine registration, this paper used the improved iteration closest point(ICP) algorithm, which took the minimum distance from point to plane as the object of iterative optimization, for accurate registration. Experimental results show that, compared with the other three registration methods, the proposed method can maintain high registration accuracy while reducing registration time. [ABSTRACT FROM AUTHOR]

Using 2-hydroxy-4-methoxybenzophenone as carbon source and ethylenediamine as nitrogen source, an oil-soluble nitrogen doped carbon dots (CDs) with dual absorption of ultraviolet and short-wave blue light is synthesized by hydrothermal method. The composite lens material with ultraviolet light and short-wave blue light shielding effect is prepared by compounding CDs with polymethyl methacrylate. When the mass fraction of CDs is 1%, the average transmittance of the composite lens in the ultraviolet region is 0%, the average transmittance in the short-wave blue light region is 1. 6%, and the absorption efficiency is 99. 6%. It is a strong anti-ultraviolet-short-wave blue light material. [ABSTRACT FROM AUTHOR]

Conservation tillage is an important measure to promote the sustainable agriculture. No-tillage sowing in straw-covered fields is an advanced farming technology of conservation tillage system, which has been widely used in northeast China because of its many advantages, such as saving production cost, protecting soil and ecological environment. However, due to the long growth cycle of corn, the straw is stronger and harder to rot. During the harvest operation in autumn, corn stalks are usually crushed by combine harvesters and scattered on the ground, but the length of the stalks crushed is inconsistent and the distribution is uneven on the ground. During the sowing operations in spring, the crushed straws are not rotten in the field, the surface flatness is relatively poor, and the sowing operating environment is worse. No-tillage finger-type precision planter is widely used in straw mulching for seeding, the above problems results in the random vibration excitation of the no-tillage planter during the operation is significantly enhanced, which seriously affect its performance, such as affecting the working quality of planters, reducing the seeding yield and uniform plant distribution, and ultimately reduces crop yields. In this paper, in order to study the vibration characteristics of 2BMZ-2 corn no-tillage finger-type precision planter and the influence of vibration on the seeding performance of corn finger-type precision seed metering device, the vibration characteristics model of the planter was established and the steady-state vibration response was solved. The vibration characteristics of the planter worked in straw mulching were measured and analyzed by field test. Based on the above theoretical analysis and field test results, a test bench for vibration seeding was built, which was used to simulate the vibration environment of the field operation and to test the influence of mechanical vibration on the performance of the seed metering device. The three-dimensional space trajectory of the falling seed was measured and analyzed by the high-speed photography and target tracking technology. The results showed that the vibration characteristics of the planter were mainly determined by the working speed, the surface of field, the soil conditions and the structural characteristics of the seed metering device. The field experimental results showed that when the working speed was in the range of 5 to 9 km/h, the vibration frequency distribution of the seed metering device vibration energy was mainly concentrated in the low frequency range of 3 to 11 Hz; the greater the working speed was, the larger the vibration acceleration was, but the vibration frequency distribution of vibration energy was not affected. The bench comparative test results showed that the mechanical vibration had no significant effect on seed filling performance of the seed metering device, but had significant effect on seeding qualified rate, coefficient of variation of spacing in longitudinal direction and coefficient of variation of spacing in transverse direction. The multi-factor quadratic general rotation combined test results showed that rotational speed, vibration acceleration and vibration frequency were the main and secondary factors influencing the uniform stability of seed arrangement, reducing the vibration acceleration can improve working quality of the seed metering device more than reducing the vibration frequency. The single factor experiment showed that, in the range of vibration frequency of 3 to 11 Hz, vibration acceleration of 0.3g to 1.5g and rotational speed of 31.5 to 57 r /min, the increase of each test factor made the seed falling trajectory and the seed falling points more discrete, and increased the range of seeding. In addition, increase the rotational speed made the position of seed falling point gradually away from the initial position of seed. The results can provide guidance for the design of the vibration-damping system of the corn finger-type precision seed metering device and corn no-tillage finger-type precision planter. [ABSTRACT FROM AUTHOR]

Insufficient soil moisture content and accumulated temperature of the plow layer during springtime tillage in Northeast China severely restrict soybean root growth and soybean development. Aiming at these issues, bionics structure design and theoretical analysis were methodologically combined to design an earthworm-like multi-function opener, which has the function of loosening, furrowing and compaction. This machine could simulate the movement of the earthworm to loose surface soil of plow layer and compact subsoil of seed ditch, which could build favorable seedbeds with soft surface soil and the compacted subsoil, and then significantly raise the soil temperature and soil moisture content of plow layer, which could significantly promote soybean emergence and development. Parameter optimization experiments and regression analysis methods were adopted to study how key structure parameters and operating speed of earthworm-like multi-function opener affected average soil temperature (0-100 mm), average soil moisture (0-100 mm) and emergence time of soybean. Experiment data obtained were assessed by the analysis of variance (ANOVA) and quadratic regression model was set up for optimization by response surface methodology with Design-Expert. Analyses showed that operating speed, scarification mechanism bump height and number of crests of corrugated disk had a significant effect (P<0.01) on average soil moisture content (0-100 mm), average soil temperature (0-100 mm) and average emergence time. Operating speed had a significant interaction with bump height and number of crests respectively and there was no interaction between bump height and number of crests. The average soil moisture content (0-100 mm) decreased with the increase of the advancing operating speed, and the decline trend gradually decreased. The average soil moisture content (0-100 mm) decreased with the increase of the bump height and the number of crests, and the decline trend gradually decreased. The average soil temperature (0-100 mm) increased with the acceleration of the operating speed, and the upward trend slowed down gradually. With the increase of bump height and the number of crests, the average soil temperature (0-100 mm) presented a rising tendency, and the rising trend decreased gradually. With the increase of operating speed, the average emergence time decreased first and then increased. The average emergence time of soybean increased after slight decrease with the increase of the height of bump. As the number of crests increased, the average emergence time decreased at first, and then rose. Earliest average emergence time was taken as main optimization index to obtain the optimal parameters by using MATLAB software based on the analysis of the test results and the model fitting. It was found that the optimal parameters of earthworm-like multi-function opener were as follows: operating speed of 8 km/h, bump height of 6 mm and number of crests of 15. Compared with traditional single disk and double-disk opener, earthworm-like multi-function opener could increase average soil water content (0-100 mm) by 5.92% and 4.86%, raise average soil temperature (0-100 mm) by 0.5 and 0.4 ℃, and advance soybean emergence time by 0.5 and 0.92 d, respectively. The results showed that the scarification furrowing mechanism which simulates the biological behavior of earthworms could effectively loosen the plow layer soil and increase the soil porosity in the plow layer so as to effectively improve the soil temperature. Meanwhile, pressure regulating mechanism could significantly accelerate the absorption of moisture from the soil beneath the plow layer by compacting subsoil of seed ditch, and then increase the soil moisture content of the soil in plow layer. This new machine can improve physical properties of the soil in tillage layer, and ultimately achieve the purpose of promoting soybean development. This is a powerful guarantee for production of soybean per unit area in Northeast China. [ABSTRACT FROM AUTHOR]

Natural biological materials generally have a perfect macro and micro compound structure. Animal’s teeth, claws and bones have formed the optimized geometry with excellent mechanical properties after a long period of evolution, and have occupied an important position in the field of engineering bionics. Teeth are an integral part of the predation process of vertebrates, which use their teeth to break prey down into small pieces, and remove the inedible parts of the prey. Bull shark is an animal with great bite force, and its teeth structure is one of the main reasons for its bite force. Taking bull shark’s maxillary and mandibular teeth as the research object, the microstructure of bull shark teeth was observed by using scanning electron microscope (SEM), the elementary composition of bull shark teeth was observed by using energy disperse spectroscopy (EDS), and the friction and wear behavior of the bull shark teeth was investigated systematically in this paper. The wear resistance of the bull shark teeth was estimated by a wear tester. Experimental results showed that enamel layer was a compact structure formed by strip fiber bundles, and the dentin was a porous structure, which holes were in the range of 3-20 μm with an irregular arrangement, and could improve the bonding strength. Compared with the dentin, the contents of calcium (Ca) and fluorine (F) in the bull shark teeth enamel were much higher, and these 2 types of elements could help teeth have better acid resistance and hardness. The surface roughness of the polished teeth sample, which contacted with Si3N4 ceramic ball, was small at first. Therefore, the enamel of bull shark’s maxillary and mandibular teeth had a low initial friction coefficient. After a period of time, due to fatigue damage in the enamel surface and brittle cracking, the friction coefficient rapidly increased in the enamel material with the peeling of teeth. The friction coefficient of the 2 different samples changed with time and presented different trends. The friction coefficient of the maxillary teeth showed a rapid increase after 60 s, while the time for the mandibular teeth was 35 s. The flake wear debris peeled off in the surface of bull shark enamel, and the surface was attached to a lot of fine abrasive particles. The maxillary teeth wear volume was 1.72×107 μm3, and the wear debris peeling was mainly caused by fatigue wear; the mandibular teeth presented obvious cracking phenomenon, and the wear volume was 2.11×107 μm3, higher than the maxillary teeth. The friction and wear experimental results showed that the abrasion resistance of maxillary teeth was better than that of mandibular teeth because the maxillary teeth are responsible for cutting their prey, but the mandibular teeth are only responsible for piercing prey in the process of long-term predation. This paper provides a reference for the design of a new type of cutlery and the experiment data and theoretical basis for the study of the tribology properties of animal teeth in the future by observing the microstructure and testing the friction properties. [ABSTRACT FROM AUTHOR]