•Constructed three types datasets of multi-cultivar tea shoots under field conditions.•Built 18 multi-cultivar tea shoots detection models based on deep learning methods.•Analyzed the influence of ...training parameters, types of datasets, and transfer learning on detection performance.•The proposed optimal training strategy significantly improved the detection performance.
Accurate detection of tea shoots in the field conditions is vital to intelligent tea picking, field management, yield prediction, or phenotypic analysis. In the strategic planning of tea plantation construction, the multiple cultivars planting pattern is usually adopted for regulating production peaks and mitigating losses caused by pests, diseases, or natural disasters. Previous studies on tea shoots detection are mostly focused on the single cultivar, with limited exploration into multi-cultivar. Therefore, the study utilized deep learning methods to investigate detecting multi-cultivar tea shoots and optimized the training strategy to improve the detection performance. Firstly, images of tea shoots of three cultivars were acquired under field conditions to construct different types of datasets based on labeling methods and contained cultivars (named as: multi-cultivar and hybrid label dataset, multi-cultivar and multi-label dataset, and single cultivar datasets). Secondly, several tea shoots detection models based on the Faster RCNN and YOLO series were built and analyzed to determine the baseline network model. To improve the detection performance, the training parameters of the baseline network model were optimized. Meanwhile, the training effects of different models based on three types of datasets and transfer learning with various pre-training weights were compared. The study results show that YOLOv7 achieved the highest detection performance with the mean average precision of 82.4 %, while consuming fewer computational resources. The giga floating-point operations per second was 105.1 and frames per second was 59.5. The model trained on multi-cultivar and multi-label dataset with a batch size of 2, 200 epochs and pre-training weights derived from the MS COCO dataset, achieved a mean average precision of 87.1 % in detecting multi-cultivar tea shoots. Optimal training strategy was made through optimizing training parameters, multi-label method and transfer learning, which significantly improved the detection performance of the network model, and the mean average precision increased 4.7 %. The study achieved accurate detection of multi-cultivar tea shoots, providing technical and theoretical support for the development of intelligent tea field management and mechanized picking.
What affects the transition of a collection of grains from flowing to a rigid packing? Previous efforts towards answering this important question have led to various versions of ``jamming’’ phase ...diagrams, which specify conditions under which a granular material behaves like solid, i.e., in a jammed phase. In this dissertation, we report two sets of experiments to study the influence of particle shape and of the form of the applied shear strain on the jamming phase diagram of slowly deformed frictional granular materials. We use 2d photoelastic particles to measure the overall pressure of the system and various physical quantities that characterize the contact network such as the averaged number of contacts per particle. In the first set of experiments, we systematically compare the mechanical and geometrical properties of uniaxially compressed granular materials consisting of particles with shapes of either regular pentagon or disk. The compression is applied quasi-statically and induces a density-driven jamming transition. We find that pentagons and disks jam at similar packing fraction. At the onset of jamming, disks have contact numbers consistent with predictions from an ideal constraint counting argument. However, this argument fails to predict the right contact number for pentagons. We also find that both jammed pentagons and disks show the Gamma distribution of the Voronoi cell area with the same parameters. Moreover, jammed pentagons have similar translational order for particle centers but slightly less orientational order for contacting pairs compared to jammed disks. Finally, we report observations that for jammed pentagons, the angle between edges at a face-to-vertex contact point shows a uniform distribution and the size of a cluster connected by face-to-face contacts shows a power-law distribution. In the second set of experiments, we use a novel multi-ring Couette shear apparatus that we developed to eliminate shear banding which unavoidably appears in conventional Couette shear experiments. A shear band is a narrow region where a lot of rearrangements of particles occur. The shear band usually has a much smaller packing fraction than the rest of the system. We map out a jamming phase diagram experimentally, and for the first time perform a systematic direct test of the mechanical responses of the jammed states created by shearing under reverse shear. We find a clear distinction between fragile states and shear-jammed states: the latter do not collapse under reverse shear. The yield stress curve is also mapped out, which marks the stress needed for the shear-jammed states to enter a steady regime where many plastic rearrangements of particles happen and the overall stress fluctuates around a constant. Interestingly, for large packing fraction, a shear band still develops when the system remains strongly jammed in the steady regime. We find that the cooperative motion of particles in this regime is highly heterogeneous and can be quantified by a dynamical susceptibility, which keeps growing as the packing fraction increases. Our observations not only serve as important data to construct theories to explain the origin of rigidity in density-driven jamming and shear-induced jamming but also are relevant to many other key problems in the physics of granular matter from the stability of a jammed packing to the complex dynamics of dense granular flows.
We investigate the jamming transition in a quasi-2D granular material composed of regular pentagons or disks subjected to quasistatic uniaxial compression. We report six major findings based on ...experiments with monodisperse photoelastic particles with static friction coefficient
μ
≈
1
. (1) For both pentagons and disks, the onset of rigidity occurs when the average coordination number of non-rattlers,
Z
nr
, reaches 3, and the dependence of
Z
nr
on the packing fraction
ϕ
changes again when
Z
nr
reaches 4. (2) Though the packing fractions
ϕ
c
1
and
ϕ
c
2
at these transitions differ from run to run, for both shapes the data from all runs with different initial configurations collapses when plotted as a function of the non-rattler fraction. (3) The averaged values of
ϕ
c
1
and
ϕ
c
2
for pentagons are around
1
%
smaller than those for disks. (4) Both jammed pentagons and disks show Gamma distribution of the Voronoi cell area with same parameters. (5) The jammed pentagons have similar translational order for particle centers but slightly less orientational order for contacting pairs compared to jammed disks. (6) For jammed pentagons, the angle between edges at a face-to-vertex contact point shows a uniform distribution and the size of a cluster connected by face-to-face contacts shows a power-law distribution.
The study on the deposition efficiency of pesticide droplets on soybean leaves can provide the basis for reducing pesticide quantity and increasing pesticide efficiency during the application of ...soybean plant protection machinery. The movement behavior of droplet impinges on the plant leaf surface is affected by many factors, among which the most important and the easiest to adjust are spray droplet size and impingement velocity. By changing the droplet size and impact velocity and using Fluent simulation software, the pesticide droplet hitting the soybean leaf surface was simulated and a test platform was established to verify the simulation results. The conclusions are as follows: The longitudinal roughness of soybean leaves is higher than the transverse roughness, the longitudinal pressure of soybean leaves is higher than the transverse pressure during the impact process, and the velocity of droplet spreading along the longitudinal is lower than that of spreading along the transverse; although soybean leaf surface has high adhesion, droplet losses still exist when droplet impact velocity is relatively high. The maximum spreading diameter of the droplet increases first and then decreases with the increase of impact velocity. At the same time, the maximum spreading diameter of droplet increases with the increase of particle size. The droplet deposition was best at 1.34 m/s impact velocity and 985 ym particle size. This conclusion can provide optimal operation parameters for soybean plant protection operation which can be used to guide soybean plant protection operation, improve control effect, reduce quantity and increase efficiency.
We systematically investigated the impact of boundary confinement on the
shear-thickening rheology of dense granular suspensions. Under highly confined
conditions, dense suspensions were found to ...exhibit size-dependent or even
rarely reported non-monotonic ($S$-shaped) flow curves in steady states. By
performing in-situ boundary stress microscopy measurements, we observed
enhanced flow heterogeneities in confined suspensions, where concentrated
high-stress domains propagated stably either along or against the shear
direction. By comparing the boundary stress microscopy results with macroscopic
flow responses, we revealed the connection between non-monotonic rheology and
stress heterogeneity in confined suspensions. These findings suggest the
possibility of controlling suspension rheology by imposing different boundary
confinements.
The strain-rate sensitivity of confined granular materials has been widely explored, with most findings exhibiting rate-strengthening behaviors. This study, however, reveals a distinct rate-softening ...behavior across a certain strain rate range based on triaxial tests on particle clusters of various materials with different surface properties, particle sizes, shapes, and stiffness. This softening effect is especially pronounced in the case of common rice particles. By examining the behavior of rice particles under different confining pressure and surface conditions, and directly measuring the frictional coefficient across various loading rates, we find that the reduction in surface frictional coefficient with the increasing strain rate predominantly contributes to this rate-softening behavior. This conclusion is validated by results from Finite Element Method (FEM) simulations. Additionally, we identify confining pressure as a critical factor regulating the normal stress between particles, and thereby enhancing frictional behavior. Rheometer tests reveal that the shear modulus exhibits a similar rate-softening trend. This study of rate-softening behavior in granular materials enhances our understanding of the mechanisms during their deformation under confining pressure. It also suggests that local inter-particle tribology significantly impacts overall granular behavior.
Soft composite solids are made of inclusions dispersed within soft matrices. They are ubiquitous in nature and form the basis of many biological tissues. In the field of materials science, synthetic ...soft composites are promising candidates for building various engineering devices due to their highly programmable features. However, when the volume fraction of the inclusions increases, predicting the mechanical properties of these materials poses a significant challenge for the classical theories of composite mechanics. The difficulty arises from the inherently disordered, multi-scale interactions between the inclusions and the matrix. To address this challenge, we systematically investigated the mechanics of densely filled soft elastomers containing stiff microspheres. We experimentally demonstrated how the strain-stiffening response of the soft composites is governed by the critical scalings in the vicinity of a shear-jamming transition of the included particles. The proposed criticality framework quantitatively connects the overall mechanics of a soft composite with the elasticity of the matrix and the particles, and captures the diverse mechanical responses observed across a wide range of material parameters. The findings uncover a novel design paradigm of composite mechanics that relies on engineering the jamming properties of the embedded inclusions.
In a recent paper Phys. Rev. X 12, 031021, we reported experimental observations of ``ultrastable'' states in a shear-jammed granular system subjected to small-amplitude cyclic shear. In such states, ...all the particle positions and contact forces are reproduced after each shear cycle so that a strobed image of the stresses and particle positions appears static. In the present work, we report further analyses of data from those experiments to characterize both global and local responses of ultrastable states within a shear cycle, not just the strobed dynamics. We find that ultrastable states follow a power-law relation between shear modulus and pressure with an exponent \(\beta\approx 0.5\), reminiscent of critical scaling laws near jamming. We also examine the evolution of contact forces measured using photoelasticimetry. We find that there are two types of contacts: non-persistent contacts that reversibly open and close; and persistent contacts that never open \yiqiu{and display no measurable sliding}. We show that the non-persistent contacts make a non-negligible contribution to the emergent shear modulus. We also analyze the spatial correlations of the stress tensor and compare them to the predictions of a recent theory of the emergent elasticity of granular solids, the Vector Charge Theory of Granular mechanics and dynamics (VCTG) Phys. Rev. Lett. 125, 118002, arXiv:2204.11811. We show that our experimental results can be fit well by VCTG, assuming uniaxial symmetry of the contact networks. The fits reveal that the response of the ultrastable states to additional applied stress is substantially more isotropic than that of the original shear-jammed states. Our results provide important insight into the mechanical properties of frictional granular solids created by shear.
Dry granular materials such as sand, gravel, pills, or agricultural grains, can become rigid when compressed or sheared. At low density, one can distort the shape of a container of granular material ...without encountering any resistance. Under isotropic compression, the material will reach a certain {\it jamming} density and then resist further compression. {\em Shear jamming} occurs when resistance to shear emerges in a system at a density lower than the jamming density, and the elastic properties of such states have important implications for industrial and geophysical processes. We report on experimental observations of changes in the mechanical properties of a shear-jammed granular material subjected to small-amplitude, quasi-static cyclic shear. We study a layer of plastic discs confined to a shear cell, using photoelasticimetry to measure all inter-particle vector forces. For sufficiently small cyclic shear amplitudes and large enough initial shear, the material evolves to an unexpected "ultra-stable" state in which all the particle positions and inter-particle contact forces remain unchanged after each complete shear cycle for thousands of cycles. The stress response of these states to small imposed shear is nearly elastic, in contrast to the original shear jammed state.
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