Experimental Study on Creep Behavior and Crack Evolution of Stratified Structural Sandstone under Segmental Constant Load

The hazards induced by stratified rock mass creep are still one of the major problems that threaten the safety of underground engineering. This paper takes safe construction of underground roadway in Urumqi mining area as the research background. In this study, we mainly adopted rock mechanics experiments to accomplish the research on creep behavior and crack evolution of stratified structural sandstone. Creep deformation characteristics of stratified structural sandstone under different load were revealed; also, we analyzed the reason why a part of rock samples failed but others were not under the same load. Creep behavior and crack evolution of rock samples without stratified structure have significant randomness. The crack evolution and failure characteristics of stratified structural rock samples were mainly manifested as failure along and cutting through structural plane and their combined forms. Creep strain, creep duration, and creep rate of rock samples with stratified structure had a nonlinear relationship with applied load, such as exponential function or logarithmic function. Understanding the evolutionary relationship between the above parameters and load provides a basis for obtaining the creep behavior of stratified rock mass under different load conditions.

Enhanced cube implementation for highly stratified population

A balanced sampling design should always be the adopted strategy if auxiliary information is available. In addition, integrating a stratified structure of the population in the sampling process can considerably reduce the variance of the estimators. We propose here a new method to handle the selection of a balanced sample in a highly stratified population. The method improves substantially the commonly used sampling designs and reduces the time-consuming problem that could arise if inclusion probabilities within strata do not sum to an integer.

Decellularized Articular Cartilage Microparticles for Expansion of Mesenchymal Stem Cells and Zonal Regeneration of Articular Cartilage

Introduction: The objective was to create multilayer cellular constructs using fetal or adult, decellularized articular cartilage in particulate form as microcarriers for expansion and fusion of mesenchymal stem cells (MSCs) to regenerate the stratified structure of articular cartilage. Methods: Porous microparticles (CMPs) generated from decellularized fetal or adult bovine articular cartilage were used as microcarriers for expansion of human MSCs. The CMP expanded MSCs (CMP-MSCs) were used to generate injectable hydrogels or preformed multilayer constructs for articular cartilage regeneration. In the injectable approach, CMP-MSCs were suspended in alginate gel, crosslinked with calcium chloride, and incubated in chondrogenic medium to generate an injectable regenerative construct. In the preformed approach, fetal or adult CMP-MSCs were suspended in a culture medium, allowed to settle sequentially by the force of gravity, and fused by incubation in chondrogenic medium to generate multilayer cell sheets. The constructs were characterized with respect to compressive modulus, cellularity, and expression of chondrogenic markers. Results: Human MSCs expanded on fetal or adult CMPs in basal medium maintained the expression of mesenchymal markers. The injectable CMP-MSCs hydrogels had significantly higher expression of chondrogenic markers and compressive modulus after four weeks incubation in chondrogenic medium compared to MSCs directly encapsulated in alginate gel; preformed CMP-MSCs cell sheets had significantly higher compressive modulus and expression of chondrogenic markers compared to MSCs in the pellet culture. Conclusion: The preformed cell sheet approach is potentially useful for creating multilayer constructs by sequential gravitational settling of CMP-MSCs to mimic the stratified structure of articular cartilage.

INTEGRATION OR SEGREGATION IN SOCIETIES (The case study of Education system in Israel)

In all economically developed societies, we find a fair amount of inter-generational mobility and at the same time clear patterns of continuity between the status of the family of origin in society and the education and income of the offspring. The desire of those who advocate equal opportunity is to minimize as much as possible this inter-generational continuity by increasing the chances of children from the lower part of the stratified structure to reach higher levels of education and income. This article will describe the process of the Israeli minorities and their integration or segregation the context of Educational integration in the country.