Biyolofi

A comprehensive computational analysis is performed to investigate the nature of rarefied gas flow through a backward-facing step duct. A characteristic-based split Navier-Stokes FEM solver is used for the simulations of the flows found in slip regime. The second-order slip-velocity and temperature-jump boundary conditions of Beskok and Karniadakis are applied on the duct walls. Changing flow and heat transfer behavior of the flow due to the varying conditions characterized with non-dimensional parameters are presented and discussed in this article.

Purpose -The purpose of this paper is to present a computational study to investigate the effects of rectangular cavity design of a piezoelectrically driven micro-synthetic-jet actuator on generated flow. Design/methodology/approach -Flow simulations were done using a compressible Navier-Stokes solver, which is based on finite element method implementation of a characteristic-based-split (CBS) algorithm. The algorithm uses arbitrary Lagrangian-Eulerian formulation, which allows to model oscillation of the synthetic jet's diaphragm in a realistic manner. Since all simulated flows are in the slip-flow-regime, a second order slip-velocity boundary condition was applied along the cavity and orifice walls. Flow simulations were done for micro-synthetic-jet configurations with various diaphragm deflections amplitudes, cavity heights, and widths. All of the simulation results were compared with each other and evaluated in terms of the exit jet velocities, slip-velocities on the orifice wall and instantaneous momentum fluxes at the jet exit. Findings -It is shown that compressibility and rarefaction have important effects on the flow field generated by the micro-synthetic-jet actuator. The effect of the geometrical parameters of the cavity to important flow features such slip and phase lag are presented. Originality/value -The paper reports results of a systematical study of the flow field inside a micro-scale synthetic-jet actuator, providing designers of such devices additional information for sizing the cavity within slip flow regime. Furthermore, it is demonstrated that the CBS, together with slip boundary conditions can be successfully used to compute such flows.

Gas flow in micro-electro-mechanical systems can be considered as rarefied since the ratio of free molecular path length to the characteristic length of the device is high. It is possible to analyse these flows using a conventional Navier–Stokes solver with modified boundary conditions to account for temperature-jump and slip-velocity on solid walls. In this study, characteristic-based-split (CBS) algorithm is modified to account for slip-velocity and temperature-jump boundary conditions in order to perform compressible flow analysis for a micro sized geometry. The CBS algorithm is a split procedure which yields a unified solution method valid for both compressible and incompressible flows. To verify the modified CBS solver, straight micro channel and micro step duct geometries are selected as test cases. To reduce the size of the implicit part of the algorithm, pseudo-quadratic velocity/linear pressure elements (pP2P1) are employed. The results obtained using CBS algorithm, are compared with other analytical and computational results available in the literature. It is shown that this implementation of the CBS algorithm is applicable and effective for micro gas flows. It is also shown that, increasing Knudsen number results in increased temperature-jump and slip-velocity. This effect, however, is limited, especially for high Mach number flows. Copyright © 2006 John Wiley & Sons, Ltd.

Ders Kurulu: 204 Dersin Adı: Beyin Zarları ve Sinüsleri Özet: Beyin dıştan içe doğru dura mater cranialis (encephali), arachnoidea mater cranialis ve pia mater cranialis denilen zarlar tarafından sarılıdır. Bu zarların hepsine birden meninges denir. Dura mater cranialis'in lamina externa (periosteal-endosteal tabaka) ve lamina interna (meningeal tabaka) olmak üzere iki tabakası vardır. Bu iki tabaka birbirine sıkıca yapışıktır. Ancak bu tabakalar belli yerlerde birbirlerinden ayrılarak içerisinde beyinvenöz kanının bulunduğu, beyin venöz sinüslerini (sinus durae matris)'i oluşturur. Dura mater cranialis'in lamina interna'sı cavum cranii'ye uzantılar gönderir. Bunlar falx cerebri, tentorium cerebelli, fax cerebelli ve diaphragma sella olarak isimlendirilir. Bu uzantılar beynin cavum cranii içinde daha stabil bir pozisyonda kalmasını sağlar. Arachnoidea mater cranialis dura mater ile pia mater arasında bulunan ince damardan yoksun bir membrandır. Gyrus'ların üzerinde seyreder, sulcuslara girmez. Dura mater ile arachnoidea mater arasında subdural aralık (spatium subdurale) denilen bir boşluk bulunur. Bu boşluk içinde seröz bir sıvı bulunur. Arachnoidea mater ile pia mater arasında ise içinde beyinomurilik sıvısının dolaştığı subarachnod aralık (spatium subarachnoidea) vardır. Beynin alt yüzünde ve beyin sakı çevresinde arachnodea mater ile pia mater arasında cisternae subarachnoideae denilen geniş bir boşluk yer alır. Pia mater cranialis, beynin hemen dışında yer alan bir zardır. Beynin venöz sinüsleri: Cerebral venler aracılığıyla beyinden gelen venöz kan ve granulationes arachnoidae aracılığıyla subarachnoid aralıktan gelen beyin omurilik sıvısı, bu venöz sinüsler aracılığıyla drene olur. Beyin venöz sinüsleri, sinus sagittalis superior ve inferior, sinus rectus, sinus transversus, sinus sigmoideus, sinus occipitalis, sinus cavernosus, sinus sphenoparietalis, sinus petrosus superior ve inferior'dur. Öğretim Üyesi: Prof.Dr. Meserret Cumhur Ders Kurulu: 204 Dersin Adı: Merkez Sinir Sistemi: Efferent Yollar Özet: Tractus corticospinalis kortex'in 4, 6 ve 8 numaralı motor sahaları ile 3, 2, 1, 5 ve 7 numaralı duyu sahalarından başlar. Bu lifler motor homongolos denilen bir yapı şeklinde başlar. Motor lifler capsula interna'nın crus posterior'unun genu'ya yakın kısımlarından geçerler. Sonra mesencephalon'da crus cerebri'den pons'ta eminentia pyramidalis'ten, bulbus'ta pyramis'ten geçerler. Pyramis'in alt kısmında bu liflerin %90'nı çapraz yaparlar. Karşıya geçen bu liflerin çapraz yaptıkları yere decussatio pyramidorum denir. Çapraz yapan liflerin oluşturdukları yola tractus corticospinalis lateralis, çapraz yapmayan liflerin