Stress concentration targeted reinforcement using multi-material based 3D printing

Topological engineering (3D printing into complex geometry) has emerged as a pragmatic approach to develop high specific strength (high strength and low density) lightweight structures. These complex lightweight structures fail at high-stress concentration regions, which can be, replaced with soft/tough material using 3D printing. It can improve mechanical properties such as strength, toughness and energy absorption etc. Here, we have developed stress concentration targeted multi-material schwarzite structures by 3D printing technique. The soft (Thermoplastic Polyurethane) material is reinforced at high-stress concentration regions of hard (Polylactic acid) schwarzite structures to enhance the specific yield strength and resilience. The mechanical properties and responses of these structures were then assessed via uniaxial compression tests. The multi-materials 3D printed composite structure shows improved mechanical properties compared to single materials architecture. The specific resilience of composites demonstrates remarkable enhancements, with percentage increases of 204.70 %, 596.50 %, and 1530.99 % observed when compared to hard primitives, and similarly impressive improvements of 182.45 %, 311.64 %, and 477.75 % observed in comparison to hard gyroids. The obtained experimental findings were comprehensively examined and validated with molecular dynamics (MD) simulations. The promising characteristics of these lightweight multi-material-based Schwarzites structures can be utilized in various fields such as energy harvesting devices, protective, safety gears, and aerospace components

First principles calculation of uniaxial magnetic anisotropy and magnetostriction in strained CMR films

We performed first - principles relativistic full-potential linearized augmented plane wave calculations for strained tetragonal ferromagnetic La(Ba)MnO$_3$ with an assumed experimental structure of thin strained tetragonal La$_{0.67}$Ca$_{0.33}$MnO$_3$ (LCMO) films grown on SrTiO$_3$[001] and LaAlO$_3$[001] substrates. The calculated uniaxial magnetic anisotropy energy (MAE) values, are in good quantitative agreement with experiment for LCMO films on SrTiO$_3$ substrate. We also analyze the applicability of linear magnetoelastic theory for describing the stain dependence of MAE, and estimate magnetostriction coefficient $\lambda_{001}$.Comment: Talk given at APS99 Meeting, Atlanta, 199

Investment in Electricity Networks with Transmission Switching

We consider the application of Dantzig-Wolfe decomposition to stochastic integer programming problems arising in the capacity planning of electricity trans-mission networks that have some switchable transmission elements. The decomposition enables a column-generation algorithm to be applied, which allows the solution of large problem instances. The methodology is illustrated by its application to a problem of determining the optimal investment in switching equipment and transmission capacity for an existing network. Computational tests on IEEE test networks with 73 nodes and 118 nodes confirm the efficiency of the approach

A hidden Goldstone mechanism in the Kagom\'e lattice antiferromagnet

In this paper, we study the phases of the Heisenberg model on the \kagome lattice with antiferromagnetic nearest neighbour coupling $J_1$ and ferromagnetic next neighbour coupling $J_2$. Analysing the long wavelength, low energy effective action that describes this model, we arrive at the phase diagram as a function of $\chi = \frac{J_2}{J_1}$. The interesting part of this phase diagram is that for small $\chi$, which includes $\chi =0$, there is a phase with no long range spin order and with gapless and spin zero low lying excitations. We discuss our results in the context of earlier, numerical and experimental work.Comment: 21 pages, latex file with 5 figure

Star-graph expansions for bond-diluted Potts models

We derive high-temperature series expansions for the free energy and the susceptibility of random-bond $q$-state Potts models on hypercubic lattices using a star-graph expansion technique. This method enables the exact calculation of quenched disorder averages for arbitrary uncorrelated coupling distributions. Moreover, we can keep the disorder strength $p$ as well as the dimension $d$ as symbolic parameters. By applying several series analysis techniques to the new series expansions, one can scan large regions of the $(p,d)$ parameter space for any value of $q$. For the bond-diluted 4-state Potts model in three dimensions, which exhibits a rather strong first-order phase transition in the undiluted case, we present results for the transition temperature and the effective critical exponent $\gamma$ as a function of $p$ as obtained from the analysis of susceptibility series up to order 18. A comparison with recent Monte Carlo data (Chatelain {\em et al.}, Phys. Rev. E64, 036120(2001)) shows signals for the softening to a second-order transition at finite disorder strength.Comment: 8 pages, 6 figure

Thermoelectric power of MgB2−x_{2-x}Bex_x

We investigated thermoelectric power $S(T)$ of MgB$_{2-x}$Be$_{x}$ ($x=0$, 0.2, 0.3, 0.4, and 0.6). $S(T)$ decreases systematically with $x$, suggesting that the hole density increases. Our band calculation shows that the increase occurs in the $\sigma$-band. With the hole-doping, $T_{c}$ decreases. Implication of this phenomenon is discussed within the BCS framework. While the Mott formula explains only the linear part of $S(T)$ at low temperature, incorporation of electron-phonon interaction enables us to explain $S(T)$ over wide temperature range including the anomalous behavior at high temperature.Comment: 4 pages, 4 figure

Direct Mott Insulator-to-Superfluid Transition in the Presence of Disorder

We introduce a new renormalization group theory to examine the quantum phase transitions upon exiting the insulating phase of a disordered, strongly interacting boson system. For weak disorder we find a direct transition from this Mott insulator to the Superfluid phase. In d > 4 a finite region around the particle-hole symmetric point supports this direct transition, whereas for 2=< d <4 perturbative arguments suggest that the direct transition survives only precisely at commensurate filling. For strong disorder the renormalization trajectories pass next to two fixed points, describing a pair of distinct transitions; first from the Mott insulator to the Bose glass, and then from the Bose glass to the Superfluid. The latter fixed point possesses statistical particle-hole symmetry and a dynamical exponent z, equal to the dimension d.Comment: 4 pages, Latex, submitted to Physical Review Letter

Heisenberg exchange enhancement by orbital relaxation in cuprate compounds

We calculate the Heisenberg exchange J in the quasi-2D antiferromagnetic cuprates La2CuO4, YBa2Cu3O6, Nd2CuO4 and Sr2CuO2Cl2. We apply all-electron (MC)SCF and non-orthogonal CI calculations to [Cu2O11]18-, [Cu2O9]14-, [Cu2O7]10- and [Cu2O7Cl4]14- clusters in a model charge embedding. The (MC)SCF triplet and singlet ground states are well characterized by Cu2+ (dx2-y2) and O2-. The antiferromagnetic exchange is strongly enhanced by admixing relaxed (MC)SCF triplet and singlet excited states, in which a single electron is transferred from the central O ion to Cu. We ascribe this effect to orbital relaxation in the charge transfer component of the wave function. Close agreement with experiment is obtained.Comment: publishe