Repeated Loading Model for Elastic-Plastic Contact of Geomaterial

A new nonlinear hysteretic model with considering the loading, unloading, and reloading processes is developed based on Drucker—Prager yield criterion and finite-element analysis. This model can be used for multiple repeated elastic—plastic normal direction contact problems between two identical spherical geomaterials. After examining the influence of material properties, strain hardening, and loading histories, we found that the hysteretic phenomena (represented by residual displacement and plastic work) become weak after the first cycle, and the subsequent cycles step into elastic shakedown state eventually. A critical number of cycles can be used to estimate the state of ratchetting, plastic shakedown, as well as elastic shakedown. It also found that the subsequent curves will be stiffer than the previous ones, especially when the yield strength is high and ratchetting effect is not strong. This new model can be used for a wide range of geomaterials under different loading levels, and it can also be extended to describe the constitutive behavior of spheres under earthquake as well as aftershocks

A Simple Model for Elastic-Plastic Contact of Granular Geomaterials

We propose a simple elastic-plastic contact model by considering the interaction of two spheres in the normal direction, for use in discrete element method (DEM) simulations of geomaterials. This model has been developed by using the finite element method (FEM) and nonlinear fitting methods, in the form of power-law relation of the dimensionless normal force and displacement. Only four parameters are needed for each loading-unloading contact process between two spheres, which are relevant to material properties evaluated by FEM simulations. Within the given range of material properties, those four parameters can be quickly accessed by interpolating the data appended or by regression functions supplied. Instead of the Von Mises (V-M) yield criterion, the Drucker-Prager (D-P) criterion is used to describe the yield behavior of contacting spheres in this model. The D-P criterion takes the effects of confining pressure, the intermediate principal stress, and strain rate into consideration; thus, this model can be used for DEM simulation of geomaterials as well as other granular materials with pressure sensitivity

Seismic Earth Pressures of Retaining Wall from Large Shaking Table Tests

To ascertain seismic response of retaining wall in the Wenchuan earthquake, large shaking table tests are performed and an acceleration record is acted in 3 directions. In the tests, acceleration time history recorded at Wolong station in the Wenchuan earthquake is used to excite the model wall. Results from the tests show that the location of dynamic resultant earth pressure is 0.35–0.49 H from toe of the wall for road shoulder retaining wall on rock foundation, 0.33–0.42 H for embankment retaining wall on rock foundation, and 0.46–0.77 H for road shoulder retaining wall on soil foundation. Besides, dynamic earth pressure increases with the increase of ground shaking from 0.1 g to 0.9 g and the relationship is nonlinear. The distribution is closed to for PGA less than 0.4 g but larger for PGA larger than and equal to 0.4 g, especially on the soil foundation. After the comparison of measured earth pressures and theoretical results by pseudodynamic method and pseudostatic method, results of the former are consistent with those of the shaking table test, but results of the latter method are smaller than measured

New Developments in Geotechnical Earthquake Engineering

Based on the review on the advances of several important problems in geotechnical seismic engineering, the authors propose the initial analysis theory of time-frequency-amplitude (known as TFA for short), in an effort to realize the organic combination of time and frequency information and develop a groundbreaking concept to the traditional idea in the geotechnical seismic engineering area

A continuum-based model on axial pile-head dynamic impedance in inhomogeneous soil

peer reviewe

De novo sequencing and comparative transcriptome analysis of white petals and red labella in Phalaenopsis for discovery of genes related to flower color and floral differentation

Phalaenopsis is one of the world’s most popular and important epiphytic monopodial orchids. The extraordinary floral diversity of Phalaenopsis is a reflection of its evolutionary success. As a consequence of this diversity, and of the complexity of flower color development in Phalaenopsis, this species is a valuable research material for developmental biology studies. Nevertheless, research on the molecular mechanisms underlying flower color and floral organ formation in Phalaenopsis is still in the early phases. In this study, we generated large amounts of data from Phalaenopsis flowers by combining Illumina sequencing with differentially expressed gene (DEG) analysis. We obtained 37 723 and 34 020 unigenes from petals and labella, respectively. A total of 2736 DEGs were identified, and the functions of many DEGs were annotated by BLAST-searching against several public databases. We mapped 837 up-regulated DEGs (432 from petals and 405 from labella) to 102 Kyoto Encyclopedia of Genes and Genomes pathways. Almost all pathways were represented in both petals (102 pathways) and labella (99 pathways). DEGs involved in energy metabolism were significantly differentially distributed between labella and petals, and various DEGs related to flower color and floral differentiation were found in the two organs. Interestingly, we also identified genes encoding several key enzymes involved in carotenoid synthesis. These genes were differentially expressed between petals and labella, suggesting that carotenoids may influence Phalaenopsis flower color. We thus conclude that a combination of anthocyanins and/or carotenoids determine flower color formation in Phalaenopsis. These results broaden our understanding of the mechanisms controlling flower color and floral organ differentiation in Phalaenopsis and other orchids

Therapeutic Angiogenesis of PLGA-Heparin Nanoparticle in Mouse Ischemic Limb

Objective. To evaluate the possibility and efficacy of the nanoparticle encapsulating heparin as a novel delivery system to treat ischemic disease. Methods. Firstly, to synthesize the PLGA heparin and test the surface morphology, the average diameter, the loading efficiency, and the release time in vitro, then inject the PLGA heparin into mouse ischemic limbs to observe the perfusion recovery with LDPI at the time of postischemic 7, 14, 21, and 28 days, and, finally, test the expression of VEGF and HGF, the number of the neovessels and record the necrotic score of ischemic limbs. Results. The surface morphology of the PLGA heparin was smooth, the average diameter was 297 nm, the loading efficiency was 5.35%, and the release period maintained for 14 days. In animal experiment, the perfusion recovery, HGF expression level, and capillary density in PLGA-heparin group were significantly higher than that in control group, and this was consistent with less ischemic limb necrosis. Conclusion. Nanoparticle encapsulating heparin could be successful and efficient in ischemic disease. The therapeutic angiogenesis of PLGA heparin might be due to the prolongation of its biological effects with stimulating growth factor expression