Onset of convection in a finite two-dimensional container due to unipolar injection of ions

This work addresses the stability of a two-dimensional plane layer of a dielectric liquid enclosed in wall bounded cavities of different aspect ratios and subjected to unipolar injection of ions. Numerical simulations have been conducted to investigate the effect of lateralwalls, especially in the development of the electroconvective instability. It is found that an unexpected change of the bifurcation nature occurs for certain cavity aspect ratios. We showthat above the linear stability threshold for the rest state a supercritical bifurcation arises. This bifurcation takes place at a given value Tc1 of the parameter T (the electric Rayleigh number). Then, a second subcritical bifurcation occurs at a second threshold Tc2, featuring a typical hysteresis loop with an associated nonlinear criterion Tf , which is very characteristic of the Coulomb-driven convection. This behavior has been confirmed by different numerical codes based on different numerical methods. The physical mechanism which leads to this situation is analyzed and discussed. The evolution of the bifurcation diagrams with the aspect ratio of the cavity is also provided and analyzed.Ministerio de ciencia y tecnología FIS2011-25161Junta de Andalucía P10-FQM-5735Junta de Andalucía P09-FQM-458

Complex flow patterns at the onset of annular electroconvection in a dielectric liquid subjected to an arbitrary unipolar injection

We numerically investigated the annular electroconvection that takes place in a dielectric liquid lying between two concentric cylinder electrodes. A uniform injection of arbitrary strengths either from the inner or outer cylinder introduces free charge carriers into the system, and the resulting Coulomb force induces electroconvection. The problem is characterized by a linear instability that corresponds to the onset of flow motion. The linear stability criteria were determined from direct numerical results and by linear stability analysis, and the results obtained with the two approaches show an excellent agreement. We focused on the fully developed flow pattern in the finite amplitude regime. We observed very different flow motions that were highly dependent on the injection strength.Ministerio de Ciencia y Tecnología FIS2011-25161Junta de Andalucía P10-FQM-5735Junta de Andalucía P09-FQM-458

On two-dimensional finite amplitude electro-convection in a dielectric liquid induced by a strong unipolar injection

The hydrodynamic stability of a dielectric liquid subjected to strong unipolar injection is numerically investigated. We determined the linear criterion Tc (T being the electric Rayleigh number) and finite amplitude one Tf over a wide range of the mobility parameter M. A noticeable discrepancy is shown for Tf between our numerical prediction and the value predicted by stability analysis, which is due to the velocity field used in stability analysis. Recent studies revealed a transition of the flow structure from one cell to two with an increase in T. We demonstrate that this transition results in a new subcritical bifurcationMinisterio de Ciencia y Tecnología FIS2011-25161Junta de Andalucía P10-FQM-5735Junta de Andalucía P09-FQM-458

Electrohydrodynamic linear stability analysis of dielectric liquids subjected to unipolar injection in a rectangular enclosure with rigid sidewalls

We investigate the linear stability threshold of a dielectric liquid subjected to unipolar injection in a 2D rectangular enclosure with rigid boundaries. A finite element formulation transforms the set of linear partial differential equations that governs the system into a set of algebraic equations. The resulting system poses an eigenvalue problem. We calculate the linear stability threshold, as well as the velocity field and charge density distribution, as a function of the aspect ratio of the domain. The stability parameter as a function of the aspect ratio describes paths of symmetry-breaking bifurcation. The symmetry properties of the different linear modes determine whether these paths cross each other or not. The resulting structure has important consequences in the non-linear behavior of the system after the bifurcation points.Ministerio de ciencia y tecnología FIS2011-25161Junta de Andalucía P10-FQM-5735Junta de Andalucía P09-FQM-458

Electroconvection in a dielectric liquid between two concentric half-cylinders with rigid walls: Linear and nonlinear analysis

We study the linear stability and nonlinear behavior of the electroconvection between two concentric halfcylinders with no-slip conditions on all boundaries. The no-slip condition makes impossible to apply the standard modal approach. Hence, we apply a finite element technique similar to the one we have used in a previous paper about the electroconvection in a rectangular enclosed domain. When compared to the classical problem of electroconvection between two full concentric cylinders, the linear criterion is higher, due to the viscous shear introduced by the lateral walls. As a consequence, the structure of the eigenmodes is very different. There is a repulsion between modeswith the same symmetry, forcing pairs of modes to cross each other repeatedly. For inner injection and small value of the ratio between the inner and outer radii the no-slip condition changes the nature of the bifurcation from subcritical to supercritical, while it is always subcritical for outer injection. To understand this behavior, we perform a modal analysis using the eigenfunctions obtained from the linear stability analysis as modal basis. We show that the supercritical branch is originated by the nonorthogonality of the modes when no-slip boundary conditions are imposed. These mechanism explains the previously unexplained appearance of the supercritical branch in the enclosed rectangular configuration.Ministerio de Economía y Competitividad FIS2014-54539-

Finite amplitude electroconvection induced by strong unipolar injection between two coaxial cylinders

We perform a theoretical and numerical study of the Coulomb-driven electroconvection flow of a dielectric liquid between two coaxial cylinders. The specific case where the inner to outer diameter ratio is 0.5 is analyzed. A strong unipolar injection of ions either from the inner or outer cylinder is considered to introduce free charger carriers into the system. A finite volume method is used to solve all governing equations including Navier-Stokes equations and a simplified set of Maxwell’s equations. The flow is characterized by a subcritical bifurcation in the finite amplitude regime. A linear stability criterion and a nonlinear one that correspond to the onset and stop of the flow motion, respectively, are linked with a hysteresis loop. In addition, we also explore the behavior of the system for higher values of the stability parameter. For inner injection, we observe a transition between the patterns made of 7 and 8 pairs of cells, before an oscillatory regime is attained. Such a transition leads to a second finite amplitude stability criterion. A simple modal analysis reveals that the competition of different modes is at the origin of this behavior. The charge density as well as velocity field distributions are provided to help understanding the bifurcation behavior.Ministerio de ciencia y tecnología FIS2011-25161Junta de Andalucía P10-FQM-5735Junta de Andalucía P09-FQM-458

Numerical Study of a Plane Poiseuille Channel Flow of a Dielectric Liquid Subjected to Unipolar Injection

In this paper, the interaction between a plane Poiseuille channel flow and an electroconvective movement induced by the electric field is numerically investigated. A flow is generated by an inlet parabolic profile in a rectangular duct. Space charges are injected in the flow through a metallic electrode placed on one of the channel walls and brought to a given potential. Transient numerical simulations have been carried out to investigate the structure of the flow. The entire set of the coupled Navier-Stokes and EHD equations is solved using an efficient finite volume technique. The behavior of the flow subjected to an applied voltage between the two electrodes is analyzed and time evolution of the charge density distributions is presented. The interaction between the convective movement induced by space charge injection and electric field and the mainstream flow, emphasizes the appearance of periodic transverse traveling waves convected in the channel. The dynamic of the flow through the variation of the ionic mobility parameter M is investigated. For a given Reynolds number and ionoc mobility parameter M it exists a threshold value Tc of the instability parameters T above which the transverse traveling rolls appear or not. When T is increased, different flow regimes have been highlighted starting from a complete steady state up to a fully unsteady electro-plumes flow configuration

Charge injection enhanced natural convection heat transfer in horizontal concentric annuli filled with a dielectric liquid

The natural convection heat transfer in a highly insulating liquid contained between two horizontal concentric cylinders is shown by two-dimensional numerical simulations to be noticeably enhanced by imposing a direct current electric field. This augmentation of heat transfer is due to the radial flow motion induced by unipolar injection of ions. It is found that there exists a threshold of the electric driving parameter T, above which the heat transfer enhancement due to the electric effect becomes significant. For relatively small T values, the mean Nusselt numbers are closely related to the flow pattern and Rayleigh number Ra. In addition, for sufficiently high T values, the flow is fully dominated by the Coulomb force, and thus the heat transfer rate no long depends on Ra.Ministerio de Ciencia y Tecnología FIS2011-25161Junta de Andalucía P10-FQM-5735Junta de Andalucía P09-FQM-458

Numerical evaluation of heat transfer enhancement due to annular electroconvection induced by injection in a dielectric liquid

Two-dimensional numerical simulations are carried out to evaluate the enhancement of natural convection heat transfer in a dielectric liquid resulting from injection induced annular electro-convection. The liquid is confined between two concentric horizontal cylinders and subjected to the simultaneous actions of a direct current electric field and a thermal gradient. A unipolar injection from the inner cylinder introduces free space charges into the liquid. Numerical results are presented for the configuration of inner to outer diameter ratio of 0.5 and silicon oil as the working medium. It is found that the charge injection may induce a strong radial fluid motion, which consequently augments the heat transfer rate. Due to the linear stability nature of electro-convection, there exists a threshold value of the electric driving parameter, above which the electrical enhancement becomes manifest. In addition, when the electric driving parameter is sufficiently high, the flow is fully dominated by the Coulomb force, and thus heat transfer becomes independent of the thermal driving parameter.Ministerio de Ciencia y Tecnología FIS2011-25161Junta de Andalucía P10-FQM-5735Junta de Andalucía P09-FQM-458

The role of p53 in genotoxic stress-induced CIRP expression

There are a lot of insults that cause DNA damage in cells, including endogenous (e.g. ROS) or exogenous factors (e.g. UV irradiation, chemical agents, etc.). In response to genotoxic stress, there are four responses in cells to maintain genome integrity: (1)cell cycle arrest (2)apoptosis (3)transcription (4)DNA repair . It is well establish that p53 plays an important role in DNA damage response. p53 is the most frequently mutated tumor suppressor gene in human cancers. p53 is a transcription factor that upsugulates expression transcription of numerous downstream genes. A number of UV irradiation-induced genes have been identified in mammalian cells, including CIRP, also called A18 hnRNP, which encodes an RNA-binding protein and appears to function by protecting cells against UV irradiation. In our study, we demonstrated that p53 is required for the induction of CIRP expression after UV irradiation, as UV fails to induce CIRP expression in human colon cancer cell HCT116 cells with TP53 gene deletion (p53-/-) . Furthermore, we cloned human CIRP promoter and constructed CIRP promoter plasmid to document that CIRP is one of the downstream target genes of p53. On the other hand, we discovered that after UV irradiation or treatment with anti cancer drug cisplatin or etoposide, the survival rate of HCT116 p53+/+ cells is higher than HCT116 p53-/- cells. Moreover, CIRP expression is induced by cisplatin treatment but not etoposide in HCT116 p53+/+ cells. These results indicate that induction of CIRP expression is dependent on the types genotoxic stress, and suggests that CIRP could play a role in protecting cells against DNA damage in cells with p53.縮寫字對照表 I 中文摘要 III 英文摘要 V 序論 1 ㄧ、前言 1 二、p53 基因文獻回顧 1 三、CIRP文獻回顧 11 四、抗癌藥物介紹 13 研究動機與目的 16 實驗材料 17 實驗方法 18 ㄧ、細胞株之培養與繼代 18 二、細胞株之冷凍保存與解凍 18 三、細胞計數 19 四、紫外線照射細胞株 19 五、化學藥品處理細胞株 19 六、細胞存活率試驗 20 七、細胞總量RNA之萃取 20 八、反轉錄聚合酶鏈鎖反應與cDNA沈澱 21 九、即時定量聚合酶連鎖反應 22 十、CIRP啟動子與基因的選殖 24 十一 TP53 ORF 的選殖 24 十二 PCR產物存化與雙限制酶切割選殖載體與PCR產物 25 十三、膠體DNA萃取 25 十四、選殖載體與PCR產物的結合作用與定序分析 25 十五、總蛋白之萃取 26 十六、蛋白濃度定量分析 26 十七、西方點墨法 27 十八、轉型作用 30 十九、質體DNA的微量抽取 31 二十、質體的中量抽取 31 二ㄧ、報導基因冷光測定 32 試劑配方 33 實驗結果 34 ㄧ、紫外光對於人類大腸直腸癌細胞株HCT116 p53蛋白的影響34 二、紫外光對於人類大腸直腸癌細胞株HCT116 CIRP基因的表現34 三、在紫外光刺激細胞下p53蛋白對於CIRP基因的表現 34 四、p53蛋白能夠活化CIRP promoter區域 35 五、細胞基因毒性與p53蛋白表現的關聯 36 六、抗癌藥物與CIRP表現之關係 37 討論 40 結語 46 實驗結果圖表 47 附錄 57 參考文獻 6