Locking-free compressible quadrilateral finite elements: Poisson’s ratio-dependent vector interpolants

In any high-quality viscoplastic calculation, the objectivity related to shape and constitutive parameter indifference is desirable, especially when a continuous deformation into concavity is tracked. In the physical x?y frame, quadratic displacement vectors—explicitly coupled via Poisson’s ratio—encompass bar and Euler–Bernoulli beam modes. Analytically, the unique set of shape functions yields nodal loads and the element stiffness matrix from its area and the first and second area moments. Closed-form Mathematica results exhibit full compliance with all requirements of Iron’s patch tests.     

Estimation of skin impedance models with experimental data and a proposed model for human skin impedance

The skin is a complex biological tissue whose impedance varies with frequency. The properties and structure of skin changes with the location on the body, age, geographical location and other factors. Considering these factors, skin impedance analysis is a sophisticated data analysis. However, despite all these variations, various researchers have always worked to develop an equivalent electrical model of the skin. The two most important categories of electrical models are RC‐based model and CPE‐based model which focus on the physiological stratification and biological properties of skin, respectively. In this work, experimental skin impedance data is acquired from ten sites on the body to find the fitting model. It is observed that a hybrid of fractional‐order CPE‐based model and higher‐order RC layered‐based model can provide the best fitting electrical model of skin. A new model is developed with this hybrid orders. Genetic algorithm is used for the extraction of parameter components. Least error of fitting has been observed for the proposed model as compared with the other models. This model can be used in correlating many skin problems and in the development of diagnostic tools. It will offer an additional supportive tool in‐vitro to the medical specialist.Inspec keywords: genetic algorithms, skin, data analysis, bioelectric phenomena, medical computing, electric impedance, patient diagnosisOther keywords: skin impedance models, human skin impedance, skin impedance analysis, data analysis, electrical models, RC‐based model, biological properties, experimental skin impedance data, fractional‐order CPE‐based model, skin problems, complex biological tissue, higher‐order RC layered‐based model, genetic algorithm, diagnostic tools     

A novel channel-identification method for wireless communication systems

We present a novel dual-channel identification approach for mobile wireless communication systems. Unlike traditional channel-estimation methods that rely on training symbols, we propose a bent-pipe feedback mechanism which requires the mobile station (MS) to send portions of its received signal back to the base station (BS) for wireless channel identification. Using a filter-bank decomposition concept, we introduce an effective algorithm that can identify both the forward and the reverse channels based only on this feedback information. This new method permits transfer of computational burden from the MS to the resource-rich BS, and leads to significant savings in bandwidth-consuming training signals.     

Crystal structure, thermal expansion and electrical conductivity of Nd0.7Sr0.3Fe1−xCoxO3 (0≤x≤0.8)

The crystal structure, thermal expansion and electrical conductivity of the solid solution Nd_0.7Sr_0.3Fe_1−xCo_xO₃ for 0≤x≤0.8 were investigated. All compositions had the GdFeO₃-type orthorhombic perovskite structure. The lattice parameters were determined at room temperature by X-ray powder diffraction (XRPD). The pseudo-cubic lattice constant decreased continuously with x. The average linear thermal expansion coefficient (TEC) in the temperature range from 573 to 973 K was found to increase with x. The thermal expansion curves for all values of x displayed rapid increase in slope at high temperatures. The electrical conductivity increased with x for the entire temperature range of measurement. The calculated activation energy values indicate that electrical conduction takes place primarily by the small polaron hopping mechanism. The charge compensation for the divalent ion on the A-site is provided by the formation of Fe⁴⁺ ions on the B-site (in preference to Co⁴⁺ ions) and vacancies on the oxygen sublattice for low values of x. The large increase in the conductivity with x in the range from 0.6 to 0.8 is attributed to the substitution of Fe⁴⁺ ions by Co⁴⁺ ions. The Fe site has a lower small polaron site energy than Co and hence behaves like a carrier trap, thereby drastically reducing the conductivity. The non-linear behaviour in the dependence of log σT with reciprocal temperature can be attributed to the generation of additional charge carriers with increasing temperature by the charge disproportionation of Co³⁺ ions.     

A Branching Time Temporal Framework for Quantitative Reasoning

Temporal logics such as Computation Tree Logic (CTL) and Linear Temporal Logic (LTL) have become popular for specifying temporal properties over a wide variety of planning and verification problems. In this paper we work towards building a generalized framework for automated reasoning based on temporal logics. We present a powerful extension of CTL with first-order quantification over the set of reachable states for reasoning about extremal properties of weighted labeled transition systems in general. The proposed logic, which we call Weighted Quantified Computation Tree Logic (WQCTL), captures the essential elements common to the domain of planning and verification problems and can thereby be used as an effective specification language in both domains. We show that in spite of the rich, expressive power of the logic, we are able to evaluate WQCTL formulas in time polynomial in the size of the state space times the length of the formula. Wepresent experimental results on the WQCTL verifier.     

Force and energy calculations in metal shearing using inclined knife profile

For selection and design of the correct size of shears, it is essential to know the values of shearing force and shearing energy and the cutting speed. Accurate values of shearing force and energy can only be obtained from the actual force-penetration characterstics for specific shearing applications. Actual force-penetration characteristics for all varieties of metal having different compositions and in use at various temperatures are not always available. In this paper, methods have been proposed for calculating approximate values of shearing force and energy for cutting different shapes with inclined knife profiles. Formulae to calculate shearing force and energy are derived from mathematical models with certain assumed deviations from the actual cutting process. Published experimental data for specific applications are included for discussion.     

A higher-order triangular plate bending element revisited

A new formulation of an eighteen-degrees-of-freedom higher-order triangular plate bending element using triangular area co-ordinates is presented. The displacement function w is taken as the complete fifth-order polynomial in area co-ordinates. The normal slope along an edge of the triangle is constrained to vary cubically. The twenty-one constants are expressed explicity in terms of eighteen degrees of freedom. The element stiffness matrix is expressed as a product of component matrices for which explicit expressions are developed and presented. No numerical inversion or integration is necessary. The formulation is expected to be useful specially for microcomputers.     

Microstructural evolution of AISI 4340 steel during Direct Metal Deposition process

In the current investigation AISI 4340 steel was laser deposited on a rolled mild steel substrate by Direct Metal Deposition (DMD) technology. The microstructural investigation of the clad was performed using optical and electron microscopes and X-ray diffraction techniques. The microstructure consisted of ferrite, martensite and cementite phases. Two types of martensite, lathe-type and plate-type, were observed in the microstructure. Decrease in microhardness values from the top layer to the alloy layer proves that the degree of tempering of the martensite phase increases in the same direction. The lattice parameters of the identified phases were found to be shorter than those reported in literature. The reported parameters in literature are from samples processed under equilibrium conditions.