Technique for Calculating Solution Derivatives With Respect to Geometry Parameters in a CFD Code

A solution has been developed to the challenges of computation of derivatives with respect to geometry, which is not straightforward because these are not typically direct inputs to the computational fluid dynamics (CFD) solver. To overcome these issues, a procedure has been devised that can be used without having access to the mesh generator, while still being applicable to all types of meshes. The basic approach is inspired by the mesh motion algorithms used to deform the interior mesh nodes in a smooth manner when the surface nodes, for example, are in a fluid structure interaction problem. The general idea is to model the mesh edges and nodes as constituting a spring-mass system. Changes to boundary node locations are propagated to interior nodes by allowing them to assume their new equilibrium positions, for instance, one where the forces on each node are in balance. The main advantage of the technique is that it is independent of the volumetric mesh generator, and can be applied to structured, unstructured, single- and multi-block meshes. It essentially reduces the problem down to defining the surface mesh node derivatives with respect to the geometry parameters of interest. For analytical geometries, this is quite straightforward. In the more general case, one would need to be able to interrogate the underlying parametric CAD (computer aided design) model and to evaluate the derivatives either analytically, or by a finite difference technique. Because the technique is based on a partial differential equation (PDE), it is applicable not only to forward mode problems (where derivatives of all the output quantities are computed with respect to a single input), but it could also be extended to the adjoint problem, either by using an analytical adjoint of the PDE or a discrete analog

Electrical properties of individual tin oxide nanowires contacted to platinum electrodes

A simple and useful experimental alternative to field-effect transistors for measuring electrical properties free electron concentration nd, electrical mobility , and conductivity in individual nanowires has been developed. A combined model involving thermionic emission and tunneling through interface states is proposed to describe the electrical conduction through the platinum-nanowire contacts, fabricated by focused ion beam techniques. Current-voltage I-V plots of single nanowires measured in both two- and four-probe configurations revealed high contact resistances and rectifying characteristics. The observed electrical behavior was modeled using an equivalent circuit constituted by a resistance placed between two back-to-back Schottky barriers, arising from the metal-semiconductor-metal M-S-M junctions. Temperature-dependent I-V measurements revealed effective Schottky barrier heights up to BE= 0.4 eV

Cloud Computing and Dependency: An ERA of Computing

Cloud Computing offers an entirely new way of looking at IT infrastructure. Cloud Computing system fundamentally provide access to large pools of data and computational resources through a variety of interfaces similar in spirit to existing grid and programming system. Cloud Computing eliminates an up-front commitment by users, thereby allowing agencies to start small and increases hardware resources only when there is an increase in their needs. Moreover,cloud computing provides the ability to pay for use of computing resources in a short term basis as needed and release them as needed. In this paper we focus on architecture, types of cloud services, characteristics, advantages & disadvantages and security of cloud computing

A solution adaptive structured-unstructured grid procedure for unsteady flows

A solution adaptive hybrid grid method for the computation of two-dimensional, unsteady flows is presented. The method is capable of handling multiple component, complex geometries in relative motion, such as those encountered in turbomachinery analysis. The numerical approach uses a hybrid structured-unstructured zonal grid topology along with modeling equations and solution techniques that are most appropriate in the individual domains, thus combining the advantages of both structured and unstructured grid methods. The viscous flow region in the immediate vicinity of the airfoils is resolved using a third-order accurate, implicit, upwind solution of the Navier-Stokes equations on structured, O-type grids. Explicit solutions of the Euler equations are obtained in the rest of the domain that consists of an unstructured mesh made up of triangular cells. The use of both central- and upwind-differenced flux schemes is investigated for the unstructured domains. Methodologies for accurate, conservative transfer of information at the interface between the structured and unstructured domains as well as that between two unstructured grids in relative motion are developed. An efficient and robust solution adaptation strategy is developed which incorporates both refinement and de-refinement capabilities for the unstructured grid regions. Both time-averaged and time-resolved results are presented for test cases and are compared with available experimental data. The quality of the results obtained by the present method is comparable with those obtained by methods based on fully structured grids. Calculations performed using the solution adaptation capabilities are also presented

Electron attachment to valence-excited CO

The possibility of electron attachment to the valence $^{3}\Pi$ state of CO is examined using an {\it ab initio} bound-state multireference configuration interaction approach. The resulting resonance has $^{4}\Sigma^{-}$ symmetry; the higher vibrational levels of this resonance state coincide with, or are nearly coincident with, levels of the parent $a^{3}\Pi$ state. Collisional relaxation to the lowest vibrational levels in hot plasma situations might yield the possibility of a long-lived CO$^-$ state.Comment: Revtex file + postscript file for one figur

Extended 16x16 Play-Fair Algorithm for Secure Key Exchange Using RSA Algorithm

With the world entering in the 21st century rigorous efforts are being made to secure data and flow of information among the users. Though with the advancements are fast and efficient the third party intervention and security threats has also increased many folds. The algorithms being used to encrypt and decrypt data needs to be strong enough to secure the data but also simple enough for a user to handle the process. With this article a novel, practical approach is presented which not only makes the information more secured but also being based on RSA algorithm is easy enough for users to understand and implement into the systems

The Operator Product Expansion of N=4 SYM and the 4-point Functions of Supergravity

We give a detailed Operator Product Expansion interpretation of the results for conformal 4-point functions computed from supergravity through the AdS/CFT duality. We show that for an arbitrary scalar exchange in AdS(d+1) all the power-singular terms in the direct channel limit (and only these terms) exactly match the corresponding contributions to the OPE of the operator dual to the exchanged bulk field and of its conformal descendents. The leading logarithmic singularities in the 4-point functions of protected N=4 super-Yang Mills operators (computed from IIB supergravity on AdS(5) X S(5) are interpreted as O(1/N^2) renormalization effects of the double-trace products appearing in the OPE. Applied to the 4-point functions of the operators Ophi ~ tr F^2 + ... and Oc ~ tr FF~ + ..., this analysis leads to the prediction that the double-trace composites [Ophi Oc] and [Ophi Ophi - Oc Oc] have anomalous dimension -16/N^2 in the large N, large g_{YM}^2 N limit. We describe a geometric picture of the OPE in the dual gravitational theory, for both the power-singular terms and the leading logarithms. We comment on several possible extensions of our results.Comment: 42 page

Influence of precursor chemistry on CVD grown TiO2 coatings: differential cell growth and biocompatibility

Nanocrystalline titanium oxide (TiO2) coatings with different phases and surface topographies were deposited using chemical vapor deposition (CVD) of different homo- and heteroleptic titanium precursors of general formula [XTi(OiPr)3] (X = Cl (1), -NEt2 (2), -N(SiMe3)2 (3), -C5H5 (4), -OiPr (5) and -OtBu (6)) to elucidate the influence of molecular configuration on resulting material properties. The interdependence of precursor chemistry and materials features of the CVD deposits was verified by performing film growth under similar conditions using different precursor molecules (1-6). Studies on composition (XPS), structure (SEM, XRD) and bio-functional properties (cell tests) revealed that the decomposition process is markedly influenced by the auxiliary ligands, which led to incorporation of heteroelements (Si, Cl, N) in the films. Cell tests performed to evaluate the biocompatibility of the coatings towards the growth of bone cells showed a pronounced correlation between cell adhesion and surface morphology as well as the chemical composition. Growth of osteoblast cells was strongly enhanced on films obtained using [Ti(OiPr)4] and [CpTi(OiPr)3], whereas TiO2 coatings produced by [ClTi(OiPr)3] significantly inhibited the cell growth and their proliferation due to Cl contamination. Also, the nanomorphological features of the films were found to stimulate the cell adhesion and growth