Sharif Digital Repository

In this research the cross-sectional profile of flattened wires after flat rolling are calculated for different reductions. The empirical formulation, analytical formulation and numerical method have been used to predict the cross-sectional profile. Also, the theoretical results are compared with the experimental data. It has been found that the numerical method is able to predict the lateral spread, the width of contact area, and the curvature radius in all ranges of the reduction in height with a good accuracy, while the other methods exhibit a reasonable accuracy only for a limited range of height reduction. All results of the methods show that with increasing the reduction in height, the... 

In this paper, we consider the solution of an nth order boundary-value problem. We solve this problem by changing the problem to a system of two integral-differential equations and using the variational iteration method. By giving three examples and comparing with the other methods, the efficiency of the method will be shown. © 2007 Elsevier Inc. All rights reserved  

An optimal labeling where labels are disjoint axis-parallel equal-size squares is called 2PM labeling if the labels have maximum length each attached to its corresponding point on the middle of one of its horizontal edges. In a closed-2PM labeling, no two edges of labels containing points should intersect. Removing one point and its label, makes free room for its adjacent labels and may cause a global label expansion. In this paper, we construct several data structures in the preprocessing stage, so that any point removal event is handled efficiently. We present an algorithm which decides in O (lg n) amortized time whether a label removal leads to label expansion in which case a new optimal... 

Settlement is one of the most important effects of tunnelling. In order to minimize this effect, it is necessary to arrange for circumstances to keep the strain and stress state of undisturbed soil within a tight limit. To achieve this, it is common nowadays to use closed face pressurized shields such as EPB TBMs. In this type of shield, face stability and ground settlement control is maintained by pressurizing the tunnel face with adjustment of cutter head thrust and muck removal discharge. In this paper, numerical modeling of excavation of twin tunnels in Tabriz subway is addressed with respect to the effect of EPB tunnelling in settlement control. Settlement and lining thrust are... 

The spin structure in a magnetic dot is studied as a function of the exchange coupling strength and dot size within the semiclassical approximation on a discrete lattice. As the exchange coupling is decreased or the size is increased, the ground state undergoes a phase change from a homogeneous single-domain ferromagnet (HSDF) to a spin vortex. The line separating these two phases has been calculated numerically for small system sizes. The dipolar interaction has been fully included in our calculations. Magnon frequencies in such a dot have also been calculated in both phases by the linearized equation of motion method. These results have also been reproduced from the Fourier transform of... 

We examine the effect of local thermal non-equilibrium on the evolution of the stagnant temperature field in a semi-infinite porous medium. When local thermal equilibrium pertains, the temperature field which is induced by a step change in the temperature of a plane boundary is given by the classical conduction solution involving the complementary error function. When thermal local equilibrium does not apply, then conduction takes place more rapidly in one phase than in the other, although local thermal equilibrium is always approached as time increases. This note examines the evolution of the temperature field in each phase in detail using numerical methods, and the numerical solutions are... 

We study graphs whose adjacency matrices have determinant equal to 1 or -1, and characterize certain subclasses of these graphs. Graphs whose adjacency matrices are totally unimodular are also characterized. For bipartite graphs having a unique perfect matching, we provide a formula for the inverse of the corresponding adjacency matrix, and address the problem of when that inverse is diagonally similar to a nonnegative matrix. Special attention is paid to the case that such a graph is unicyclic. © 2006 Elsevier Inc. All rights reserved  

In this paper, a unified explicit tensorial relation is sought between two stress tensors conjugate to arbitrary and general Hill strains. The approach used for deriving the tensorial relation is based on the eigenprojection method. The result is, indeed, a generalization of the relations that were derived by Farahani and Naghadabadi [1] in 2003 from a component to intrinsic form. The result is unified in the sense that it is valid for all cases of distinct and coalescent principal stretches. Also, in the case of three dimensional Euclidean inner product space, using the derived unified relation, some expressions for the conjugate stress tensors are presented. © Sharif University of... 

One important point in microflow study is the correct consideration of the Knudsen layer. In addition to the many complexities behind numerical simulation of the Knudsen layer near the solid walls, there are serious uncertainties at the microchannel inlet (the point at which the flow enters the microdomain). One major difficulty is the appearance of two singularities at the two corners of the inlet section. They seriously affect the solution in the entrance region of microchannels in which the lengths are comparable with the lengths of their hydrodynamic developing zones. Although the macro inlet flow problem has been largely investigated, there has been little attempt to study the issue in... 

Let D be a division ring with center F and n {greater than or slanted equal to} 1 a natural number. For S ⊆ Mn(D) the commuting graph of S, denoted by Γ(S), is the graph with vertex set S{minus 45 degree rule}Z(S) such that distinct vertices a and b are adjacent if and only if ab = ba. In this paper we prove that if n > 2 and A, N, I, T are the sets of all non-invertible, nilpotent, idempotent matrices, and involutions, respectively, then for any division ring D, Γ ( A ), Γ ( N ), Γ ( I ), and Γ ( T ) are connected graphs. We show that if n > 2 and U is the set of all upper triangular matrices, then for every algebraic division ring D, Γ ( U ) is a connected graph. Also it is shown that if R... 

In this work we study the problem of whether all trajectories of the system ẋ=y-F(x) and ẏ=-g(x) cross the vertical isocline, which is very important for the existence of periodic solutions and oscillation theory. Sufficient conditions are given for all trajectories to cross the vertical isocline. © 2005 Elsevier Ltd. All rights reserved  

We present a high-performance and efficiently simplified new neural network which improves the existing neural networks for solving general linear and quadratic programming problems. The network, having no need for parameter setting, results in a simple hardware requiring no analog multipliers, is shown to be stable and converges globally to the exact solution. Moreover, using this network we can solve both linear and quadratic programming problems and their duals simultaneously. High accuracy of the obtained solutions and low cost of implementation are among the features of this network. We prove the global convergence of the network analytically and verify the results numerically. © 2005... 

The star graph, as an interesting network topology, has been extensively studied in the past. In this paper, we address some of the combinatorial properties of the star graph. In particular, we consider the problem of calculating the surface area of the star graph, answering an open problem previously posed in [12]. © 2005 IEEE  

This paper proves that if G is a graph (parallel edges allowed) of maximum degree 3, then χc′(G) ≤ 11/3 provided that G does not contain H1 or H2 as a subgraph, where H1 and H2 are obtained by subdividing one edge of K23 (the graph with three parallel edges between two vertices) and K4, respectively. As χc′(H1) = χ c′(H2) = 4, our result implies that there is no graph G with 11/3 < χc′(G) < 4. It also implies that if G is a 2-edge connected cubic graph, then χc′(G) ≤ 11/3. © 2005 Wiley Periodicals, inc  

This method introduces the structural error of regression deviation, which is an effective method for the path generation of a vast type of planar and spatial mechanism. The proposed method avoids point-by-point comparison and requirement of timing and reflects the difference between the two curves very effectively in the objective function. By decreasing the number of the design variables, this method would help considerably in decreasing CPU time. The objective function that is based on regression error would converge to a global minimum by a genetic algorithm. At the end, the effectiveness of the method is shown by two numerical examples. © Sharif University of Technology  

Steady-state laminar and incompressible fluid flow and forced-convection heat transfer from a circular cylinder and an array of circular cylinders in the presence and no-presence of porous media are investigated. Various mathematical and numerical models are compared and the effects of porous media on heat transfer enhancement are studied. Navier-Stokes equations are used for the analysis of laminar fluid flow and heat transfer. However, the Darcy and extended Darcy-Brinkman models are used for the analysis of fluid flow and heat transfer in porous media. The cylinders are at constant temperature and the analysis is restricted to the low- and intermediate-Peclet-number regimes (Pr = 1, Re ≤... 

The objective of this paper is to introduce a new numerical method for neutronic calculation in a reactor core. This method can produce the final finite form of the neutron diffusion equation by classifying the neutronic variables and using two kinds of cell complexes without starting from the conventional differential form of the neutron diffusion equation. The method with linear interpolation produces the same convergence as the linear continuous finite element method. The quadratic interpolation is proven; the convergence order depends on the shape of the dual cell. The maximum convergence order is achieved by choosing the dual cell based on two Gauss' points. The accuracy of the method... 

Three-dimensional orbits in the vicinity of the collinear libration points of the Sun-Earth/Moon barycenter system are currently being considered for use with a number of missions planed for 2000 and beyond. Since such libration point trajectories are, in general, unstable, spacecraft moving on these paths must use some form of trajectory control to remain close to their nominal orbit. In this paper, circular restricted three body problem is reviewed and a numerical method to control spacecrafts on periodic halo orbits around L1 and L2 collinear points of the Sun-Earth/Moon barycenter system is investigated. The control approach is based on the optimal control theory and implements variation... 

A new model is proposed to predict the Forming Limit Diagrams (FLDs) of Tailor Welded Blanks (TWBs). This model is derived by modification of the Marciniak and Kuczynski (MK) analysis and imposing the weld constraints to deformation state of each blank at each strain increment. Based on this model, it is possible to predict the strains of both weaker and stronger blanks once necking occurs. By comparison to the experimental results of two laser welded TWBs, it is demonstrated that this model provides a close prediction of FLD of TWBs, when necking occurs far from the weld line at a region out of HAZ (Heat Affected Zone) and close to it so that it is affected by the weld line constraints  

Though wound healing process is well-researched, this area is poorly known. One reason is that all interactions have not been discovered, the main reason, though, is that the involved processes interact in a very complicated manner with nonlinear feedback. Such complex feedback mechanisms can be easily addressed by mathematical modeling. This paper contains a review of the mathematical modeling of cell interaction with extracellular matrix components during the process of dermal wound healing with focusing on remodeling phase. The models are of partial differential equation type and solved by numerical method