Three-degree-of-freedom Parallel Manipulator to Track the Sun for Concentrated Solar Power Systems

In concentrated solar power(CSP) generating stations, incident solar energy is reflected from a large number of mirrors or heliostats to a faraway receiver. In typical CSP installations, the mirror needs to be moved about two axes independently using two actuators in series with the mirror effectively mounted at a single point. A three degree-of-freedom parallel manipulator, namely the 3-RPS parallel manipulator, is proposed to track the sun. The proposed 3-RPS parallel manipulator supports the load of the mirror, structure and wind loading at three points resulting in less deflection, and thus a much larger mirror can be moved with the required tracking accuracy and without increasing the weight of the support structure. The kinematics equations to determine motion of the actuated prismatic joints in the 3-RPS parallel manipulator such that the sun's rays are reflected on to a stationary receiver are developed. Using finite element analysis, it is shown that for same sized mirror, wind loading and maximum deflection requirement, the weight of the support structure is between 15% and 60% less with the 3-RPS parallel manipulator when compared to azimuth-elevation or the target-aligned configurations.

Influence of external weld flash on the in-plane plane-strain formability of friction stir welded sheets

The main aim of the present work is to analyze the influence of external weld flash on the formability of friction stir welding sheets through in-plane plane-strain formability tests. The load-extension behavior and forming limit strains are measured to quantify the formability. The influence of friction stir welding parameters on the height of weld flash was also studied. The base materials used for welding trials are AA6061T6 and AA5052H32 alloy sheets of 2.1-mm thickness. It is observed that the influence of external weld flash on the maximum load and total extension for all the friction stir welding conditions is negligible. The effect of weld flash on the limiting major strain is also insignificant. But the presence of weld flash has changed the limiting minor strain, more toward plane-strain condition, indicating the change in strain-path toward plane-strain. This is due to the strain taken by weld flash, along with the major strain, minor strain, and thickness strain in the friction stir welding sheet plane because of constancy of volume. The formation of weld flash and its height are affected synergistically by the axial force and temperature development during friction stir welding. The higher the axial force and temperature, the higher the flash height.

L-infinity norms of holomorphic modular forms in the case of compact quotient

We prove a sub-convex estimate for the sup-norm of L-2-normalized holomorphic modular forms of weight k on the upper half plane, with respect to the unit group of a quaternion division algebra over Q. More precisely we show that when the L-2 norm of an eigenfunction f is one, parallel to f parallel to(infinity) <<(epsilon) k(1/2-1/33+epsilon) for any epsilon > 0 and for all k sufficiently large.

Phase-field elasticity model based on mechanical jump conditions

Computational models based on the phase-field method typically operate on a mesoscopic length scale and resolve structural changes of the material and furthermore provide valuable information about microstructure and mechanical property relations. An accurate calculation of the stresses and mechanical energy at the transition region is therefore indispensable. We derive a quantitative phase-field elasticity model based on force balance and Hadamard jump conditions at the interface. Comparing the simulated stress profiles calculated with Voigt/Taylor (Annalen der Physik 274(12):573, 1889), Reuss/Sachs (Z Angew Math Mech 9:49, 1929) and the proposed model with the theoretically predicted stress fields in a plate with a round inclusion under hydrostatic tension, we show the quantitative characteristics of the model. In order to validate the elastic contribution to the driving force for phase transition, we demonstrate the absence of excess energy, calculated by Durga et al. (Model Simul Mater Sci Eng 21(5):055018, 2013), in a one-dimensional equilibrium condition of serial and parallel material chains. To validate the driving force for systems with curved transition regions, we relate simulations to the Gibbs-Thompson equilibrium condition

A Variant of the Hadwiger-Debrunner (p, q)-Problem in the Plane

Let X be a convex curve in the plane (say, the unit circle), and let be a family of planar convex bodies such that every two of them meet at a point of X. Then has a transversal of size at most . Suppose instead that only satisfies the following ``(p, 2)-condition'': Among every p elements of , there are two that meet at a common point of X. Then has a transversal of size . For comparison, the best known bound for the Hadwiger-Debrunner (p, q)-problem in the plane, with , is . Our result generalizes appropriately for if is, for example, the moment curve.

Stability analysis of thick piezoelectric metal based FGM plate using first order and higher order shear deformation theory

This paper presents the stability analysis of functionally graded plate integrated with piezoelectric actuator and sensor at the top and bottom face, subjected to electrical and mechanical loading. The finite element formulation is based on first order and higher order shear deformation theory, degenerated shell element, von-Karman hypothesis and piezoelectric effect. The equation for static analysis is derived by using the minimum energy principle and solutions for critical buckling load is obtained by solving eigenvalue problem. The material properties of the functionally graded plate are assumed to be graded along the thickness direction according to simple power law function. Two types of boundary conditions are used, such as SSSS (simply supported) and CSCS (simply supported along two opposite side perpendicular to the direction of compression and clamped along the other two sides). Sensor voltage is calculated using present analysis for various power law indices and FG (functionally graded) material gradations. The stability analysis of piezoelectric FG plate is carried out to present the effects of power law index, material variations, applied mechanical pressure and piezo effect on buckling and stability characteristics of FG plate.

In-plane elastic responses of circular cell honeycombs and bundled circular tubes in a diamond array structure

Assemblages of circular tubes and circular honeycombs in close packed arrangement are presently both competing and complementing regular honeycomb structures (HCS). The intrinsic isotropy of bundled tubes/rings in hexagonal arrays restricts their use to applications with isotopic need. With the aim of extending the utility of tubes/rings assemblages to anisotropic needs, this paper explores the prospects of bundled tubes and circular honeycombs in a general diamond array structure (DAS) to cater these needs. To this end, effective transverse Young's moduli and Poisson's ratio for thick/thin DAS are obtained theoretically. Analysis frameworks including thin ring theory (TRT), curved beam theory (CBT) and elasticity formulations are tested and corroborated by FEA employing contact elements. Results indicate that TRT and CBT are reasonable for thin tubes and honeycombs. Nevertheless, TRT yields compact formulae to study the anisotropy ratio, moduli spectrum and sensitivity of the assemblage as a function of thicknesses and array structure. These formulae supplement designers as a guide to tailor the structures. On the other hand, elasticity formulation can estimate over a larger range including very thick tubes/rings. In addition, this formulation offers to estimate refined transverse strengths of assemblages. (C) 2015 Elsevier Ltd. All rights reserved.

In-plane effective shear modulus of generalized circular honeycomb structures and bundled tubes in a diamond array structure

Use of circular hexagonal honeycomb structures and tube assemblies in energy absorption systems has attracted a large number of literature on their characterization under crushing and impact loads. Notwithstanding these, effective shear moduli (G*) required for complete transverse elastic characterization and in analyses of hierarchical structures have received scant attention. In an attempt to fill this void, the present study undertakes to evaluate G* of a generalized circular honeycomb structures and tube assemblies in a diamond array structure (DAS) with no restriction on their thickness. These structures present a potential to realize a spectrum of moduli with minimal modifications, a point of relevance for manufactures and designers. To evaluate G* in this paper, models based on technical theories - thin ring theory and curved beam theory - and rigorous theory of elasticity are investigated and corroborated with FEA employing contact elements. Technical theories which give a good match for thin HCS offer compact expressions for moduli which can be harvested to study sensitivity of moduli on topology. On the other hand, elasticity model offers a very good match over a large range of thickness along with exact analysis of stresses by employing computationally efficient expressions. (C) 2015 Elsevier Ltd. All rights reserved.

Onset of plane layer magnetoconvection at low Ekman number

We study the onset of magnetoconvection between two infinite horizontal planes subject to a vertical magnetic field aligned with background rotation. In order to gain insight into the convection taking place in the Earth's tangent cylinder, we target regimes of asymptotically strong rotation. The critical Rayleigh number Ra-c and critical wavenumber a(c) are computed numerically by solving the linear stability problem in a systematic way, with either stress-free or no-slip kinematic boundary conditions. A parametric study is conducted, varying the Ekman number E (ratio of viscous to Coriolis forces) and the Elsasser number. (ratio of the Lorentz force to the Coriolis force). E is varied from 10(-9) to 10(-2) and. from 10(-3) to 1. For a wide range of thermal and magnetic Prandtl numbers, our results verify and confirm previous experimental and theoretical results showing the existence of two distinct unstable modes at low values of E-one being controlled by the magnetic field, the other being controlled by viscosity (often called the viscous mode). It is shown that oscillatory onset does not occur in the range of parameters we are interested in. Asymptotic scalings for the onset of these modes are numerically confirmed and their domain of validity is precisely quantified. We show that with no-slip boundary conditions, the asymptotic behavior is reached for E < 10(-6) and establish a map in the (E, Lambda) plane. We distinguish regions where convection sets in either through the magnetic mode or through the viscous mode. Our analysis gives the regime in which the transition between magnetic and viscous modes may be observed. We also show that within the asymptotic regime, the role played by the kinematic boundary conditions is minimal. (C) 2015 AIP Publishing LLC.

Efficient coupled polynomial interpolation scheme for out-of-plane free vibration analysis of curved beams

The performance of two curved beam finite element models based on coupled polynomial displacement fields is investigated for out-of-plane vibration of arches. These two-noded beam models employ curvilinear strain definitions and have three degrees of freedom per node namely, out-of-plane translation (v), out-of-plane bending rotation (theta(z)) and torsion rotation (theta(s)). The coupled polynomial interpolation fields are derived independently for Timoshenko and Euler-Bernoulli beam elements using the force-moment equilibrium equations. Numerical performance of these elements for constrained and unconstrained arches is compared with the conventional curved beam models which are based on independent polynomial fields. The formulation is shown to be free from any spurious constraints in the limit of `flexureless torsion' and `torsionless flexure' and hence devoid of flexure and torsion locking. The resulting stiffness and consistent mass matrices generated from the coupled displacement models show excellent convergence of natural frequencies in locking regimes. The accuracy of the shear flexibility added to the elements is also demonstrated. The coupled polynomial models are shown to perform consistently over a wide range of flexure-to-shear (EI/GA) and flexure-to-torsion (EI/GJ) stiffness ratios and are inherently devoid of flexure, torsion and shear locking phenomena. (C) 2015 Elsevier B.V. All rights reserved.

Determinantal point processes in the plane from products of random matrices

We show that the density of eigenvalues for three classes of random matrix ensembles is determinantal. First we derive the density of eigenvalues of product of k independent n x n matrices with i.i.d. complex Gaussian entries with a few of matrices being inverted. In second example we calculate the same for (compatible) product of rectangular matrices with i.i.d. Gaussian entries and in last example we calculate for product of independent truncated unitary random matrices. We derive exact expressions for limiting expected empirical spectral distributions of above mentioned ensembles.

An efficient design of serial and parallel memory using Quantum dot cellular automata

Quantum cellular automata (QCA) is a new technology in the nanometer scale and has been considered as one of the alternative to CMOS technology. In this paper, we describe the design and layout of a serial memory and parallel memory, showing the layout of individual memory cells. Assuming that we can fabricate cells which are separated by 10nm, memory capacities of over 1.6 Gbit/cm2 can be achieved. Simulations on the proposed memories were carried out using QCADesigner, a layout and simulation tool for QCA. During the design, we have tried to reduce the number of cells as well as to reduce the area which is found to be 86.16sq mm and 0.12 nm2 area with the QCA based memory cell. We have also achieved an increase in efficiency by 40%.These circuits are the building block of nano processors and provide us to understand the nano devices of the future.

Crystal structure of a tripeptide containing aminocyclododecane carboxylic acid: a supramolecular twisted parallel -sheet in crystals

The crystal structure of a tripeptide Boc-Leu-Val-Ac(12)c-OMe (1) is determined, which incorporates a bulky 1-aminocyclododecane-1-carboxylic acid (Ac(12)c) side chain. The peptide adopts a semi-extended backbone conformation for Leu and Val residues, while the backbone torsion angles of the C-,C--dialkylated residue Ac(12)c are in the helical region of the Ramachandran map. The molecular packing of 1 revealed a unique supramolecular twisted parallel -sheet coiling into a helical architecture in crystals, with the bulky hydrophobic Ac(12)c side chains projecting outward the helical column. This arrangement resembles the packing of peptide helices in crystal structures. Although short oligopeptides often assemble as parallel or anti-parallel -sheet in crystals, twisted or helical -sheet formation has been observed in a few examples of dipeptide crystal structures. Peptide 1 presents the first example of a tripeptide showing twisted -sheet assembly in crystals. Copyright (c) 2016 European Peptide Society and John Wiley & Sons, Ltd.

In-plane modulated smectic (A)over-tilde vs smectic `A' lamellar structures in poly(ethyl or propyl ether imine) dendrimers

A pair of first and second generation poly(alkyl ether imine) dendrimers is prepared, having covalently attached cholesteryl moieties at their peripheries. The pairs in each generation differ in the alkyl-linker which constitute the dendritic core moieties, even when the number of cholesteryl moieties remains uniform in each pair. The dendrimer pairs are two first and second generation poly(ethyl ether imine) and poly(propyl ether imine) dendrimers, modified with 4 and 8 cholesteryl esters at the peripheries in each pair, respectively. The dendrimer pairs exhibit differing thermotropic mesophase properties. Microscopic, thermal and X-ray diffraction studies reveal a lamellar mesophase for the first generation ethyl-, first and second generation propyl-linker dendrimers. Whereas, the second generation ethyl-linker dendrimer exhibits a layered structure with a superimposed in-plane modulation, the length of which corresponds to a rectangular column width. The role of the dendrimer core moieties with differing linkers in modifying the mesophase properties is studied. (C) 2016 Elsevier Ltd. All rights reserved.

Crystal structure of a tripeptide containing aminocyclododecane carboxylic acid: a supramolecular twisted parallel -sheet in crystals

The crystal structure of a tripeptide Boc-Leu-Val-Ac(12)c-OMe (1) is determined, which incorporates a bulky 1-aminocyclododecane-1-carboxylic acid (Ac(12)c) side chain. The peptide adopts a semi-extended backbone conformation for Leu and Val residues, while the backbone torsion angles of the C-,C--dialkylated residue Ac(12)c are in the helical region of the Ramachandran map. The molecular packing of 1 revealed a unique supramolecular twisted parallel -sheet coiling into a helical architecture in crystals, with the bulky hydrophobic Ac(12)c side chains projecting outward the helical column. This arrangement resembles the packing of peptide helices in crystal structures. Although short oligopeptides often assemble as parallel or anti-parallel -sheet in crystals, twisted or helical -sheet formation has been observed in a few examples of dipeptide crystal structures. Peptide 1 presents the first example of a tripeptide showing twisted -sheet assembly in crystals. Copyright (c) 2016 European Peptide Society and John Wiley & Sons, Ltd.