The combined effect of cohesion and finite size on the collapse of wet granular columns.

The collapse of low-saturation liquid-containing granular materials is prevalent in nature and industrial processes, and understanding the associated transient dynamics is extremely important for exploring such complex flow processes. In this paper, the collapse of a finite-size wet granular column is systematically studied and the determinants affecting its dynamics are analyzed based on the discrete element model for wet particles and the corresponding small-scale experiments. With the aid of parametric analysis, the dimensionless cohesion parameter containing the system size and grain-scale bond number is proposed, and its relevance in characterizing column stability and collapse dynamics of wet granular materials is further confirmed. For the collapse of wet granular columns with a fixed aspect ratio, the initial height contained in the cohesion parameter is verified to be a manifestation of the finite size effect, which is present in a wet granular collapse and is coupled with the cohesive effect. Such a coupling effect is taken into account in our proposed scaling laws that can be applied to uniformly describe the deposit morphology of wet granular columns after collapse.

Molecular mapping for fruit-related traits, and joint identification of candidate genes and selective sweeps for seed size in melon.

Melon is a popular fruit vegetable crop worldwide with diverse morphological variation. We report a high-density genetic map of melon and nine major QTLs with physical region ranging from 43.47 kb to 1.89 Mb. Importantly, two seed-related trait QTLs were repeatedly detected in two environments, and the mapping region was narrowed to 522 kb according to a regional linkage analysis. A total of 40 annotated genes were screened for nonsynonymous variations, of which EVM0009818, involved in cytokinin-activated signaling, was differentially expressed in the young fruits of parents based on RNA-seq. Selective sweep analysis identified 152 sweep signals for seed size, including the two seed-related QTLs and nine homologs that have been verified to regulate seed size in Arabidopsis or rice. This work illustrates the power of a joint analysis combining resequencing-based genetic map for QTL mapping and a combination of KASP genotyping and RNA-seq analysis to facilitate QTL fine mapping.

A High-Quality Melon Genome Assembly Provides Insights into Genetic Basis of Fruit Trait Improvement.

Accurate reference genomes have become indispensable tools for characterization of genetic and functional variations. Here we generated a high-quality assembly of the melon Payzawat using a combination of short-read sequencing, single-molecule real-time sequencing, Hi-C, and a high-density genetic map. The final 12 chromosome-level scaffolds cover ∼94.13% of the estimated genome (398.57 Mb). Compared with the published DHL92 genome, our assembly exhibits a 157-fold increase in contig length and remarkable improvements in the assembly of centromeres and telomeres. Six genes within STHQF12.4 on pseudochromosome 12, identified from whole-genome comparison between Payzawat and DHL92, may explain a considerable proportion of the skin thickness. In addition, our population study showed that melon domesticated at multiple times from whole-genome perspective and melons in China are introduced from different routes. Selective sweeps underlying the genes related to desirable traits, haplotypes of alleles associated with agronomic traits, and the variants from resequencing data enable efficient breeding.

Local and global avalanches in a two-dimensional sheared granular medium.

We present the experimental and numerical studies of a two-dimensional sheared amorphous material composed of bidisperse photoelastic disks. We analyze the statistics of avalanches during shear including the local and global fluctuations in energy and changes in particle positions and orientations. We find scale-free distributions for these global and local avalanches denoted by power laws whose cutoffs vary with interparticle friction and packing fraction. Different exponents are found for these power laws depending on the quantity from which variations are extracted. An asymmetry in time of the avalanche shapes is evidenced along with the fact that avalanches are mainly triggered by the shear bands. A simple relation independent of the intensity is found between the number of local avalanches and the global avalanches they form. We also compare these experimental and numerical results for both local and global fluctuations to predictions from mean-field and depinning theories.

Effect of variable particle stiffness on force propagation and mechanical response of a composite granular material.

The force propagation and mechanical response are important for understanding the elasticity and deformation of a composite granular packings. In this paper, a 2D composite granular layers composed of particles with variable stiffness is proposed, and the effect of stiffness ratio between component particles on mechanical response is mainly considered. The results show that the decrease of stiffness ratio broadens the linear range of mechanical response and enhances the elasticity of the response in a composite granular system, showing a role similar with the friction in a monodisperse granular packings. Furthermore, a phase diagram for the crossover between a single-peaked and a double-peaked response is proposed, in which the critical stiffness ratio corresponding to the occurrence of the crossover decreases with the magnitude of external loading and increases with the friction. Finally, the microscopic mechanism of the crossover of the response is further discussed based on changes in contact network and force network.

The scaling and dynamics of a projectile obliquely impacting a granular medium.

In this paper, the dynamics of a spherical projectile obliquely impacting into a two-dimensional granular bed is numerically investigated using the discrete element method. The influences of projectile's initial velocities and impacting angles are mainly considered. Numerical results show that the relationship between the final penetration depth and the initial impact velocity is very similar to that in the vertical-impact case. However, the dependence of the stopping time on the impact velocity of the projectile exhibits critical characteristics at different impact angles: the stopping time approximately increases linearly with the impact velocity for small impact angles but decreases in an exponential form for larger impact angles, which demonstrates the existence of two different regimes at low and high impact angles. When the impact angle is regarded as a parametric variable, a phenomenological force model at large impact angles is eventually proposed based on the simulation results, which can accurately describe the nature of the resistance force exerted on the projectile by the granular medium at different impact angels during the whole oblique-impact process. The degenerate model agrees well with the existing experimental results in the vertical-impact cases.

Influence of particle rotation on the oblique penetration in granular media.

The rotation of a particle has significant influence on the dynamic response of a granular bed subjected to the oblique impact of a spherical projectile. Based on the discrete element method, the dynamical behavior of two-dimensional granular media impacted obliquely by rotating particles has been examined in this work, especially for the influence of rotational angular velocity on its penetration depth. The simulations show that the incident rotational velocity will not only act on the characteristics of velocity distribution of the bed after impacting, but also influence the trajectory of the projectile qualitatively. For low angular velocities, particle rotations will significantly increase the vertical penetration depths, while the different directions of rotation will exert opposite effects on the horizontal penetration depths. In addition, the influence of particle rotation on its penetration depth will be enhanced with increasing angular velocity, but such effect will reach an asymptotic plateau for sufficiently large angular velocities. This indicates that the angular velocity has an obvious criticality. Furthermore, the variation of critical angular velocity may be linear with the impact velocity and square with the impacting angle, approximately. Finally, the influence of the initial particle rotation on the scaling law of penetration depth is also considered, and we find that the linear scaling with impact velocity is still applicable for most impact conditions.

An approach for the evaluation of synergy between antimicrobials.

Synergy can be assessed by a variety of microbiological techniques. Mathematical modelling of synergy data can accomplish similar results and may provide more information than currently available techniques. In this study a combination of 1/4 MIC of aztreonam (AZTR) and 1 MIC of ciprofloxacin (CIPX) showed synergy against Pseudomonas aeruginosa in killing curve studies (based on the two log different criteria) at the end of 24 h. However, re-growth was always observed even when bactericidal concentrations of antibiotics were present. The surviving organisms showed a two-fold increase of MIC to CIPX after the studies and this resistance was not reversible. A mathematical model to quantitatively describe this observation is proposed.