Pulsed field gradient NMR study of surface diffusion in mesoporous adsorbents

Surface diffusion of n-heptane in two mesoporous adsorbents with different morphologies of the pore network, namely Vycor random porous glass and porous silicon with linear pores, have been studied using pulsed field gradient NMR. The experimentally obtained diffusivities revealed increasing mobility of guest molecules with increasing surface coverage, indicating heterogeneity of the surface properties. The diffusion studies at different temperatures have further confirmed this hypothesis. The activation energies for surface diffusion turned out to be a function of surface coverage. The experimental results obtained are analyzed using a model of surface diffusion taking account of a distribution of the transition rates.     

Multi response optimization of process parameters based on Taguchi��Fuzzy model for coal cutting by water jet technology

The process of material cutting and fracture by high velocity water jets is a complex series of phenomena which may involve compression, tension, shear, erosion, wears, cracking, wave propagation, and cavitations damage. This makes the exact analysis of the jet cutting process to be very complicated. The problem of water jet coal cutting is a multiresponse problem. There are two output variables, depth of cut and cutting width whose optimization will result in the increase in the productivity of coal cutting. In this paper, a Taguchi?CFuzzy decision method has been used to determine the effective process parameters for improving the productivity of coal mines. The Taguchi method of experimental design is a widely accepted technique used for producing high quality products at low cost. The optimization of multiple responses in complex processes is common; therefore, to reduce the degree of uncertainty during the decision making, fuzzy rule-based reasoning was integrated with the Taguchi loss function.     

Constructive nonsmooth stabilization of triangular systems

The problem of local asymptotic continuous feedback stabilization of single-input nonlinear systems is considered here. The aim is to explicitly construct a continuous asymptotically stabilizing feedback for a class of nonlinear systems that is known to be continuous feedback asymptotically stabilizable, but for which the known results do not provide an effective method to compute the stabilizer. Computer simulations are included to show practical applicability of our approach.     

Determination of layer thickness in direct metal deposition using dimensional analysis

Direct Metal Deposition (DMD) is a blown powder laser deposition process that can be used to quickly produce fully dense metallic parts and to repair or modify high-value components. This paper illustrates the use of dimensional analysis to develop a mathematical model for the control of layer deposition in DMD. A brief explanation of the material deposition process is presented and the factors affecting the metal deposition is identified so that they can be used in modeling the height of the metal deposited. The validity of the generalized model is verified from experimental data of H13 steel and Ti material and it is found in good agreement with experimental findings.     

ACA accelerated high order BEM for Maxwell problems

The high order Boundary Element Methods for the system of Maxwell equations are discussed. Due to hierarchical construction of the bases in trial and test spaces, the matrix of the resulting system has a characteristic sub-matrix structure. The Adaptive Cross Approximation is successfully adapted and applied to the sub-matrices and almost linear complexity and memory requirements are achieved. The final system is solved by the iterative method GMRES. Numerical examples are presented.     

Bi-directional evolutionary level set method for topology optimization

A bi-directional evolutionary level set method for solving topology optimization problems is presented in this article. The proposed method has three main advantages over the standard level set method. First, new holes can be automatically generated in the design domain during the optimization process. Second, the dependency of the obtained optimized configurations upon the initial configurations is eliminated. Optimized configurations can be obtained even being started from a minimum possible initial guess. Third, the method can be easily implemented and is computationally more efficient. The validity of the proposed method is tested on the mean compliance minimization problem and the compliant mechanisms topology optimization problem.