Smoothening creases on surfaces of strain-stiffening materials

When an elastic block (e.g., an elastomer or a soft tissue) is compressed to a critical strain, the smooth surface of the block forms creases, namely, localized regions of self-contact. Here we show how this instability behaves if the solid stiffens steeply. For a solid that stiffens steeply at large strains, as the compression increases, the surface is initially smooth, then forms creases, and finally becomes smooth again. For a solid that stiffens steeply at small strains, creases will never form and the surface remains smooth for all levels of compression. We also obtain the critical conditions for the formation and disappearance of wrinkles. When the surface does become unstable, we find that creases always set in at a lower compression than wrinkles. Our findings may shed light in developing crease-resistant materials.Engineering and Applied Science

Household Assets, School Enrollment and Parental Aspirations for Children\u27s Education in Rural China: Does Gender Matter?

Using rural household data from the China Household Income Project (CHIP) 2002, this paper provides an analysis of different effects of household assets independent of family income on children’s school enrollment and parental aspirations for education, examining both outcomes by child’s gender. The study first compares the responsiveness of boys’ and girls’ enrollment to the improvement of household assets, measured as liquid assets and net worth, relative to family income. The multivariate regression analysis further detects the effects of household assets on both boys’ and girls’ school enrollment and parental aspirations for children’s future education by child’s gender. Statistical results show that, compared to family income, household assets matter more for girls’ schooling than for boys’. In addition, household net worth is significantly associated with parental aspirations for children’s education regardless of gender. This study, albeit exploratory, sheds light on child welfare and education policies in rural China

Transport Properties and Exponential n-values of Fe/MgB2 Tapes With Various MgB2 Particle Sizes

Fe/MgB2 tapes have been prepared starting with pre-reacted binary MgB2 powders. As shown by resistive and inductive measurements, the reduction of particle size to a few microns by ball milling has little influence on Bc2, while the superconducting properties of the individual MgB2 grains are essentially unchanged. Reducing the particle size causes an enhancement of Birr from 14 to 16 T, while Jc has considerably increased at high fields, its slope Jc(B) being reduced. At 4.2K, values of 5.3*10^4 and 1.2*10^3 A/cm^2 were measured at 3.5 and 10 T, respectively, suggesting a dominant role of the conditions at the grain interfaces. A systematic variation of these conditions at the interfaces is undertaken in order to determine the limit of transport properties for Fe/MgB2 tapes. The addition of 5% Mg to MgB2 powder was found to affect neither Jc nor Bc2. For the tapes with the highest Jc values, very high exponential n factors were measured: n = 148, 89 and 17 at 3.5, 5 and 10T, respectively and measurements of critical current versus applied strain have been performed. The mechanism leading to high transport critical current densities of filamentary Fe/MgB2 tapes based on MgB2 particles is discussed.Comment: Presented at ICMC 2003, 25-28 May 200

Investigation of blood flow patterns and hemodynamics in the human ascending aorta and major trunks of right and left coronary arteries using magnetic resonance imaging and computational fluid dynamics

Hemodynamic factors play a role in atherogenesis and the localization of atherosclerotic plaques. The human aorta and coronary arteries are susceptible to arterial disease, and there have been many studies of flows in models of these vessels. However, previous work has been limited in that investigations have not modeled both the geometry and flow conditions in specific individuals. The first aim of the research was to develop a methodology that combined computational fluid dynamics (CFD) and magnetic resonance imaging (MRI) to simulate the blood flow patterns found in the human aorta. The methodology included MR image processing, 3D model reconstruction and flow simulation using in vivo velocity boundary conditions obtained from phase contrast (PC)-MRI scanning. The CFD simulations successfully reproduce the unusual right-hand helical flow pattern that has been reported in the ascending aorta, giving confidence in the accuracy of the methodology. The second aim was to investigate the causes of the right-hand helical flow. It was found that the correct flow dynamics could only be produced by including the specific aortic motion caused by the beating heart; and it is concluded that this is a significant factor in producing the observed in vivo helical flow patterns. The entrance flows of coronary arteries are expected to be affected by flow in the aortic root, and the third aim was to explore these effects using models that include aorta and coronary arteries. The simulation results demonstrate that a pair of axial vortexes with different rotating directions exists in the entrance segments of the right and left coronary arteries during systole and early diastole, producing asymmetrical wall shear stress (WSS) distributions. The last aim of the research was to examine possible relationships between WSS distributions induced by the entry flow patterns and the frequency distributions of atherosclerosis in the proximal segments of coronary arteries reported in the clinical literature. A close correspondence between low WSS and higher frequency of plaque occurrence was observed. The tools developed in this study provide a promising avenue for future study of cardiovascular disease because of the ability to investigate phenomena in individual human subjects.Ph.D.Committee Chair: Giddens, P. Don; Committee Member: Bao, Gang; Committee Member: Oshinski, John; Committee Member: Taylor, Robert, W.; Committee Member: Vito, P. Raymon

Asset-Based Policy in China: Applied Projects and Policy Progress

Since the Center for Social Development (CSD) at Washington University in St. Louis introduced the idea of asset building in China in 2004, asset-based projects and policy discussion have drawn great attention from the central government and mainstream media. CSD research and consultation have played a central role in these developments