Initial surface deformations during impact on a liquid pool

A tiny air bubble can be entrapped at the bottom of a solid sphere that impacts onto a liquid pool. The bubble forms due to the deformation of the liquid surface by a local pressure buildup inside the surrounding gas, as also observed during the impact of a liquid drop on a solid wall. Here we perform a perturbation analysis to quantitatively predict the initial deformations of the free surface of the liquid pool as it is approached by a solid sphere. We study the natural limits where the gas can be treated as a viscous fluid (Stokes flow) or as an inviscid fluid (potential flow). For both cases we derive the spatio-temporal evolution of the pool surface, and recover some of the recently proposed scaling laws for bubble entrapment. When inserting typical experimental values for the impact parameters, we find that the bubble volume is mainly determined by the effect of gas viscosity

Universal mechanism for air entrainment during liquid impact

When a mm-sized liquid drop approaches a deep liquid pool, both the interface of the drop and the pool deform before the drop touches the pool. The build up of air pressure prior to coalescence is responsible for this deformation. Due to this deformation, air can be entrained at the bottom of the drop during the impact. We quantify the amount of entrained air numerically, using the Boundary Integral Method (BIM) for potential flow for the drop and the pool, coupled to viscous lubrication theory for the air film that has to be squeezed out during impact. We compare our results to various experimental data and find excellent agreement for the amount of air that is entrapped during impact onto a pool. Next, the impact of a rigid sphere onto a pool is numerically investigated and the air that is entrapped in this case also matches with available experimental data. In both cases of drop and sphere impact onto a pool the numerical air bubble volume V_b is found to be in agreement with the theoretical scaling V_b/V_{drop/sphere} ~ St^{-4/3}, where St is the Stokes number. This is the same scaling that has been found for drop impact onto a solid surface in previous research. This implies a universal mechanism for air entrainment for these different impact scenarios, which has been suggested in recent experimental work, but is now further elucidated with numerical results

Drop deformation by laser-pulse impact

A free-falling absorbing liquid drop hit by a nanosecond laser-pulse experiences a strong recoil-pressure kick. As a consequence, the drop propels forward and deforms into a thin sheet which eventually fragments. We study how the drop deformation depends on the pulse shape and drop properties. We first derive the velocity field inside the drop on the timescale of the pressure pulse, when the drop is still spherical. This yields the kinetic-energy partition inside the drop, which precisely measures the deformation rate with respect to the propulsion rate, before surface tension comes into play. On the timescale where surface tension is important the drop has evolved into a thin sheet. Its expansion dynamics is described with a slender-slope model, which uses the impulsive energy-partition as an initial condition. Completed with boundary integral simulations, this two-stage model explains the entire drop dynamics and its dependance on the pulse shape: for a given propulsion, a tightly focused pulse results in a thin curved sheet which maximizes the lateral expansion, while a uniform illumination yields a smaller expansion but a flat symmetric sheet, in good agreement with experimental observations.Comment: submitted to J. Fluid Mec

Drop Shaping by Laser-Pulse Impact

We show how the deposition of laser energy induces propulsion and strong deformation of an absorbing liquid body. Combining high speed with stroboscopic imaging, we observe that a millimeter-sized dyed water drop hit by a millijoule nanosecond laser pulse propels forward at several meters per second and deforms until it eventually fragments. The drop motion results from the recoil momentum imparted at the drop surface by water vaporization. We measure the propulsion speed and the time-deformation law of the drop, complemented by boundary-integral simulations. The drop propulsion and shaping are explained in terms of the laser-pulse energy, the drop size, and the liquid properties. These findings are, for instance, crucial for the generation of extreme ultraviolet light in nanolithography machines.Comment: Submitted as research article to Physical Review Applied, 6 pages with 6 figure

Oscillating and star-shaped drops levitated by an air-flow

We investigate the spontaneous oscillations of drops levitated above an air cushion, eventually inducing a breaking of axisymmetry and the appearance of “star drops”. This is strongly reminiscent of the Leidenfrost stars that are observed for drops floating above a hot substrate. The key advantage of this work is that we inject the airflow at a constant rate below the drop, thus eliminating thermal effects and allowing for a better control of the flow rate. We perform experiments with drops of different viscosities and observe stable states, oscillations, and chimney instabilities. We find that for a given drop size the instability appears above a critical flow rate, where the latter is largest for small drops. All these observations are reproduced by numerical simulations, where we treat the drop using potential flow and the gas as a viscous lubrication layer. Qualitatively, the onset of instability agrees with the experimental results, although the typical flow rates are too large by a factor 10. Our results demonstrate that thermal effects are not important for the formation of star drops and strongly suggest a purely hydrodynamic mechanism for the formation of Leidenfrost stars

Maximal air bubble entrainment at liquid drop impact

At impact of a liquid drop on a solid surface an air bubble can be entrapped. Here we show that two competing effects minimize the (relative) size of this entrained air bubble: For large drop impact velocity and large droplets the inertia of the liquid flattens the entrained bubble, whereas for small impact velocity and small droplets capillary forces minimize the entrained bubble. However, we demonstrate experimentally, theoretically, and numerically that in between there is an optimum, leading to maximal air bubble entrapment. Our results have a strong bearing on various applications in printing technology, microelectronics, immersion lithography, diagnostics, or agriculture.Comment: 4 page

Dynamics of deforming drops

Liquid drops play a dominant role in numerous industrial applications, such as spray coating, spray painting, inkjet printing, lithography processes, and spraying/sprinkling in agriculture or gardening. In all of these examples, the generation, flight, impact, and spreading of drops are separate stages of the corresponding industrial processes, which are all thoroughly studied for many years. This thesis focuses on drop dynamics, impact phenomena, Leidenfrost drops, and pouring flows. Based on extensive analysis and numerical results, various mechanisms by which drops can deform are resolved in detail, in both fundamental and industrial contexts. The title of the thesis, Dynamics of Deforming Drops, can be explained in two ways. Drops can be deformed and moving drops can deform another liquid surface.\ud \ud Large part of the study focuses on the small scale deformations of the liquid surface(s) at the bottom of the impacting drop/object, induced by the force exerted by the gas that is squeezed out between the falling object and the bottom surface. This can result in small air bubble entrapment, which is generally undesired in applications. The results of interferometry experiments and Boundary Integral simulations show that there exists a maximal entrained bubble size for some impact velocity. The mechanism of small air bubble entrapment applies for impact of a liquid drop onto a solid surface, impact of a liquid drop onto a (deep) pool, and impact of a solid sphere onto a pool.\ud \ud \ud Other covered subjects are the high-speed impact of a train of microdrops on a pool, instabilities at Leidenfrost drops, drop deformation induced by the impact of a picosecond laser-pulse, and pouring flows. The study of the response of drops impacted by a focused laser pulse is motivated by Extreme Ultraviolet (EUV) lithography, which is used for the creation of nanometer-sized patterns on electronic chips in, for example, mobile phones. To print the features at high resolution, one needs high energy radiation. In EUV-machines this radiation results from liquid tin sheets that are impacted by a laser-pulse, resulting in the formation of plasma. The fluid dynamics play a crucial role for improving the efficiency of the EUV machine

Cloning and characterizing embryonic stem cell lines derived from New Zealand White Rabbit embryos

本研究目的為探討紐西蘭白兔胚幹細胞（rabbit embryonic stem cells, rES cells）株之建立、培養與其細胞特性之分析。試驗一以STO（SIM mouse embryo-derived thioquanine and ouabain resistant）為飼養層細胞時，以全囊胚與免疫手術法分離內細胞群（inner cell mass, ICM）皆無法建立rES cell lines。而在MEF（mouse embryonic fibroblasts）飼養層上，其建立效率則顯著提高 (0% vs 24%)。在MEF飼養層條件下，白血病抑制因子（leukemia inhibitory factor, LIF）之添加能進一步提升rES cells建立之效率至57%。細胞株經由免疫螢光染色、西方吸漬法（Western blot）與反轉錄聚合酶反應（RT-PCR）偵測後，皆表現胚幹細胞特有多能性標誌（pluripotency marker），包括鹼性磷酸酶（alkaline phosphatase, AP）、Oct4、TRA-1-60、TRA-1-81、Nanog與Sox-2。在體外誘導分化形成類胚體（embryoid bodies, EBs）後，也發現三胚層細胞之特有標誌（MAP2、Desmin與GATA4），顯示此些細胞株具有分化之多能性。試驗二觀察單獨或共同添加LIF與纖維母細胞生長因子（basic fibroblast growth factor 2, bFGF2）對rES cells生長之影響並探討其訊息傳遞路徑。 結果顯示，rES cells 在MEF飼養層上，經由bFGF2訊息傳遞路徑 (MAPK/ERK and PI3K/AKT) 維持其不分化狀態。rES在LIF 與 bFGF2共同添加時較單獨添加LIF或 bFGF2條件之多能性標誌表現量高。以藥物抑制STAT3、MEK/ERK 與AKT之磷酸化，會造成rES cells失去自我更新能力，顯示bFGF2訊息傳遞路徑與LIF傳導路徑影響 rES cells生長與自我更新能力。試驗三以蛋白質體學方法比較纖維母細胞、與來自受精胚（f-rES）及孤雌激活胚（p-rES）之胚幹細胞蛋白質表現之差異，並進行蛋白質之鑑定。結果顯示，在三種不同細胞之間有100個蛋白質點呈現差異性。在這些蛋白質點中，91%成功鑑定出為63種已知蛋白質，這些已知蛋白質有14%是細胞核蛋白、13%屬於細胞骨架、8%屬粒線體、8%為內質網與57%存在於細胞質等相關蛋白。本研究有效率建立表現多能性標誌之rES cell lines並維持其於未分化狀態。LIF 和bFGF2可協同維持rES cell lines之多能性且表現與體細胞所缺乏之特異蛋白。未來研究將集中於誘導rES cells分化以及利用基因晶片來偵測其基因表現。The purposes of this study were to examine technical details in deriving and maintaining rabbit embryonic stem (rES) cell lines and to analyze their characteristics. In Experiment 1, when SIM mouse embryo-derived thioquanine and ouabain resistant (STO) cells were used as feeder cells, no rES cell lines were established using either intact blastocysts or inner cell mass (ICMs). On the mouse embryonic fibroblasts (MEF) feeder, rES cell lines were efficiently (24%) derived. Addition of leukemia inhibitory factor (LIF) to the cells cultured on the MEF feeders further increased the derivation efficiency (57%) of rES cells. Most of the rES cell lines expressed alkaline phosphotase (AP), SSEA-4, Oct-4, TRA-1-60 and TRA-1-81. Western-blot or RT-PCR analysis also confirmed the expression of Oct-4, Nanog, and Sox-2. When induced to form embryoid bodies (EBs) in vitro, the rES cells generated EBs with three germ layers expressing the marker genes including MAP2, Desmin and GATA4, respectively. In Experiment 2, we investigated the individual and combined effects of LIF and basic fibroblast growth factor 2 (bFGF2) on deriving and maintaining rES cell lines. First, when grown on MEF feeders, rES cell lines can be established and prevented from differentiation via bFGF2 (MAPK/ERK and PI3K/AKT) signaling. When both LIF and bFGF2 supplemented, rES cells acquired the highest expression of pluripotency markers than those supplemented solely with LIF or bFGF2. Induced dephosphorylation of STAT3, MEK/ERK and AKT by specific inhibitors suppressed their activities and caused remarkable losses of self-renewal capacity of rES cells. Experiment 3 aimed to determine the proteomics profiles of the fertilized embryo-derived and parthenote-derived ES cells, designated as f-rES and p-rES cells, respectively, and fibroblasts. Collectively, the expression levels of 100 spots differed significantly among these three cell types (P<0.05). Of those differentially expressed spots, 91% were identified and represented 63 distinct proteins. The proteins with known identities were mostly located in cytoplasmic compartments as cytoskeletal, mitochondrial, endoplasmic reticulum, and cytosolic proteins (13%, 8%, 8% and 57%, respectively) and nuclear (14%). We conclude that rES cell lines can be efficiently cloned using our current protocols and these ES cells express pluripotent stem cell makers and remain undifferentiation. LIF and FGF cooperation synergistically support stemness of rabbit ES cells and the expression of some novel key proteins distinguishes rabbit ES cells from their somatic counterpart. Further investigations will be focused on differentiation of rES cells and global screening of their gene expression profiles by microarrays which would invite more in-depth studies towards rabbit ES cell applications.Page ACKNOWLEDGMENTS--------------------------------------------------------------- i ABSTRACT (in Chinese)---------------------------------------------------------------- iii ABSTRACT (in English)---------------------------------------------------------------- v TABLE OF CONTENTS---------------------------------------------------------------- vii LIST OF TABLES------------------------------------------------------------------------ x LIST OF FIGURES----------------------------------------------------------------------- xi CHAPTER 1: Literature review-------------------------------------------------------------------------- 1 1. Abstract------------------------------------------------------------------------- 2 2. Introduction to embryonic stem (ES) cells--------------------------------- 3 3. Isolation of rES cell lines---------------------------------------------------- 7 3.1. Culture conditions for derivation and maintenance of rES cell lines----------------------------------------------------------------------- 7 3.2. Expression profiles of pluripotency genes and protein markers- 12 4. Rabbit models for biomedical research------------------------------------ 14 4.1. Retinal cells for eye diseases ----------------------------------------- 16 4.2. Rabbit ES cells for the treatment of cardiovascular diseases---- 18 4.3. Induction of ES cells into insulin-producing cells for the treatment of diabetes---------------------------------------------------- 20 4.4. Rabbit model for the study of tuberculosis ------------------------- 21 4.5. Rabbit model for the study of Alzheimer''s disease----------------- 22 4.6. Rabbit model for the study of fulminant hepatic failure---------- 23 4.7. Peyronie's disease----------------------------------------------------- 24 5. Conclusion remarks----------------------------------------------------------- 25 Page CHAPTER 2: Study 1: Culture and characterization of embryonic stem cell lines isolated from New Zealand White rabbits-------------------------------------------- 26 1. Abstract------------------------------------------------------------------------- 27 2. Introduction ------------------------------------------------------------------- 28 3. Material and method---------------------------------------------------------- 30 4. Results ------------------------------------------------------------------------- 38 5. Discussion---------------------------------------------------------------------- 48 CHAPTER 3: Study 2: LIF and FGF support stemness and self-renewal of rabbit embryonic stem cells derived from fertilized embryos--------------------------------- 52 1. Abstract------------------------------------------------------------------------- 53 2. Introduction ------------------------------------------------------------------- 54 3. Material and method---------------------------------------------------------- 57 4. Results ------------------------------------------------------------------------- 64 5. Discussion---------------------------------------------------------------------- 84 CHAPTER 4: Study 3: Proteomic analyses of rabbit embryonic stem cells derived from fertilized embryos and parthenotes------------------------------------------ 89 1. Abstract------------------------------------------------------------------------- 90 2. Introduction ------------------------------------------------------------------- 91 3. Material and method---------------------------------------------------------- 93 4. Results ------------------------------------------------------------------------- 101 5. Discussion---------------------------------------------------------------------- 120 CONCLUSIONS-------------------------------------------------------------------------- 125 APPENDICES Table 1 of the supplemental data----------------------------------------------- 128 Table 2 of the supplemental data----------------------------------------------- 134 Preparation of feeder cells ------------------------------------------------------ 139 Preparation rES cell culture medium----------------------------------------- 143 Page Karyotype Analysis-------------------------------------------------------------- 146 Alkaline phosphatase (AP) staining------------------------------------------- 148 Immunocytochemistry----------------------------------------------------------- 150 Western Blot---------------------------------------------------------------------- 152 REFERENCES---------------------------------------------------------------------------- 15