Homotopy Simulation of Dissipative Micropolar Flow and Heat Transfer from a Two-Dimensional Body with Heat Sink Effect

Non-Newtonian flow from a wedge constitutes a fundamental problem in chemical<br /> engineering systems and is relevant to processing of polymers, coating systems, etc. Motivated by such applications, the homotopy analysis method (HAM) was employed to<br /> obtain semi-analytical solutions for thermal convection boundary layer flow of incompressible micropolar fluid from a two-dimensional body (wedge). Viscous dissipation<br /> and heat sink effects were included. The non-dimensional boundary value problem<br /> emerges as a system of nonlinear coupled ordinary differential equations, by virtue of<br /> suitable coordinate transformations. The so-called Falkner-Skan flow cases are elaborated. Validation of the HAM solutions was achieved with earlier simpler models, as well as with a Nakamura finite difference method for the general model. The micropolar model employed simulates certain polymeric solutions quite accurately, and features rotary motions of micro-elements. Primary and secondary shear stress, wall couple stress, Nusselt number, microrotation velocity, and temperature were computed for the effect of<br /> vortex viscosity parameter (micropolar rheological), Eckert number (viscous dissipation),<br /> Falkner-Skan (pressure gradient) parameter, micro-inertia density, and heat sink parameter. The special cases of Blasius and stagnation flow were also addressed. It was observed from the study that the temperature and thermal boundary layer thickness are both suppressed with increasing wedge parameter and wall heat sink effect, which is beneficial to temperature regulation in polymer coating dynamics. Further, strong reverse spin was generated in the microrotation with increasing vortex viscosity, which resulted in<br /> increase in angular momentum boundary layer thickness. Also, both primary and secondary skin friction components were reduced with increasing wedge parameter. Nusselt number was also enhanced substantially with greater wedge parameter.

Akt signaling is critical for memory CD8+ T-cell development and tumor immune surveillance

Memory CD8+ T cells confer long-term immunity against tumors, and anticancer vaccines therefore should maximize their generation. Multiple memory CD8+ T-cell subsets with distinct functional and homing characteristics exist, but the signaling pathways that regulate their development are ill defined. Here we examined the role of the serine/threonine kinase Akt in the generation of protective immunity by CD8+ T cells. Akt is known to be activated by the T-cell antigen receptor and the cytokine IL-2, but its role in T-cell immunity in vivo has not been explored. Using CD8+ T cells from pdk1K465E/K465E knockin mice, we found that decreased Akt activity inhibited the survival of T cells during the effector-to-memory cell transition and abolished their differentiation into C-X-C chemokine receptor 3 (CXCR3)loCD43lo effector-like memory cells. Consequently, antitumor immunity by CD8+ T cells that display defective Akt signaling was substantially diminished during the memory phase. Reduced memory T-cell survival and altered memory cell differentiation were associated with up-regulation of the proapoptotic protein Bim and the T-box transcription factor eomesodermin, respectively. These findings suggest an important role for effector-like memory CD8+ T cells in tumor immune surveillance and identify Akt as a key signaling node in the development of protective memory CD8+ T-cell responses.