Numerical Investigation of Evaporation Induced Self-Assembly of Sub-Micron Particles Suspended in Water

Self-assembly of sub-micron particles suspended in a water film is investigated numerically. The liquid medium is allowed to evaporate leaving only the sub-micron particles. A coupled CFD-DEM approach is used for the simulation of fluid-particle interaction. Momentum exchange and heat transfer between particles and fluid and among particles are considered. A history dependent contact model is used to compute the contact force among sub-micron particles. Simulation is done using the open source software package CFDEM which basically comprises of two other open source packages OpenFOAM and LIGGGHTS. OpenFOAM is a widely used solver for CFD related problems. LIGGGHTS, a modification of LAMMPS, is used for DEM simulation of granular materials. The final packing structure of the sub-micron particles is discussed in terms of distribution of coordination number and radial distribution function (RDF). The final packing structure shows that particles form clusters and exhibit a definite pattern as water evaporates away

Micro-scale heat transfer simulation on water with molecular dynamics and hybrid approach

"July 2014."Dissertation Supervisor: Dr. Yuwen Zhang.Includes vita.Water is most widely existing liquid in the earth; beyond all question, it takes a very important role in human daily life and many applications in industrial field. The heat transfer phenomena have drawn a great attention in the past decades. In the thesis, classical molecular dynamic simulations are carried out to study thermal and dynamic properties, including thermal conductivities, specific heat capacity, and shear viscosity. Though water molecule only has three charged atoms, but a number of water molecule models exist in the literature field. In this thesis, several rigid water molecule models are selected to perform the simulation. Then a non-equilibrium molecular dynamic is conducted to study nano-bubble growth and annihilation in the liquid water with rigid TIP3P. A nano-bubble is successfully generated, and pressure and surface tension of the bubble is obtained. Contact angle of a water droplet is also getting attention from micro-cooling engineers. A non-equilibrium molecular dynamics on contact angle of nano-size water droplet on a single wall carbon nanotube plate is performed. The gap distance between nano-tube affects the contact angle somehow, and a critical distance value that achieve largest contact angle is found. Rapid boiling phenomena of thin water film on a hot copper plate is also studied due to its application in various industrial fields, such as laser cleaning, thermal ink-jet printer, medical surgery. The entire process of the boiling phenomena is observed, and a piston-like motion of the film is analyzed. To the end, due to the size limitation of classical molecular dynamics, a hybrid simulation coupling molecular dynamic and computational fluid dynamic is developed to extend the simulation size to micron based on open-source code LIGGGHTS and OpenFOAM. Heat transfer coefficient between argon flow and cold copper plate is studied and it is found that heat transfer coefficient can reach a very high value. In the future work, argon fluid could be replaced with normal liquid water moleIncludes bibliographical references (pages 128-144)

Overexpression of GATA2 Enhances Development and Maintenance of Human Embryonic Stem Cell-Derived Hematopoietic Stem Cell-like Progenitors

GATA2 is essential for the endothelial-to-hematopoietic transition (EHT) and generation of hematopoietic stem cells (HSCs). It is poorly understood how GATA2 controls the development of human pluripotent stem cell (hPSC)-derived HS-like cells. Here, using human embryonic stem cells (hESCs) in which GATA2 overexpression was induced by doxycycline (Dox), we elucidated the dual functions of GATA2 in definitive hematopoiesis before and after the emergence of CD34⁺CD45⁺CD90⁺CD38⁻ HS-like cells. Specifically, GATA2 promoted expansion of hemogenic precursors via the EHT and then helped to maintain HS-like cells in a quiescent state by regulating cell cycle. RNA sequencing showed that hPSC-derived HS-like cells were very similar to human fetal liver-derived HSCs. Our findings will help to elucidate the mechanism that controls the early stages of human definitive hematopoiesis and may help to develop a strategy to generate hPSC-derived HSCs

Overexpression of GATA2 Enhances Development and Maintenance of Human Embryonic Stem Cell-Derived Hematopoietic Stem Cell-like Progenitors

GATA2 is essential for the endothelial-to-hematopoietic transition (EHT) and generation of hematopoietic stem cells (HSCs). It is poorly understood how GATA2 controls the development of human pluripotent stem cell (hPSC)-derived HS-like cells. Here, using human embryonic stem cells (hESCs) in which GATA2 overexpression was induced by doxycycline (Dox), we elucidated the dual functions of GATA2 in definitive hematopoiesis before and after the emergence of CD34+CD45+CD90+CD38– HS-like cells. Specifically, GATA2 promoted expansion of hemogenic precursors via the EHT and then helped to maintain HS-like cells in a quiescent state by regulating cell cycle. RNA sequencing showed that hPSC-derived HS-like cells were very similar to human fetal liver-derived HSCs. Our findings will help to elucidate the mechanism that controls the early stages of human definitive hematopoiesis and may help to develop a strategy to generate hPSC-derived HSCs