Pervasive liquid metal direct writing electronics with roller-ball pen

A roller-ball pen enabled direct writing electronics via room temperature liquid metal ink was proposed. With the rolling to print mechanism, the metallic inks were smoothly written on flexible polymer substrate to form conductive tracks and electronic devices. The contact angle analyzer and scanning electron microscope were implemented to probe the inner property of the obtained electronics. An ever high writing resolution with line width and thickness as 200{\mu}m and 80{\mu}m, respectively was realized. Further, with the administration of external writing pressure, GaIn24.5 droplets embody increasing wettability on polymer which demonstrates the pervasive adaptability of the roller-ball pen electronics

Phase field simulation of dendritic microstructure in additively manufactured titanium alloy

Additive manufacturing (AM) processes for metals, such as selective laser sintering and electron beam melting, involve rapid solidification process. The microstructure of the fabricated material and its properties strongly depend on the solidification. Therefore, in order to control and optimize the AM process, it is important to understand the microstructure evolution. In this work, using Ti-6Al-4V as a model system, the phase field method is applied to simulate the microstructure evolution in additively manufactured metals. First, the fundamental governing equations are presented. Then the effects of various processing related parameters, including local temperature gradient, scan speed and cooling rate, on dendrites’ morphology and growth velocity are studied. The simulated results show that the dendritic arms grow along the direction of the heat flow. Higher temperature gradient, scan speed and cooling rate will result in small dendritic arm spacing and higher growth velocity. The simulated dendritic morphology and arm spacings are in good agreement with experimental data and theoretical predictions

Structural Change in an Open Economy

We develop a tractable, three-sector model to study structural change in an open economy. The model features an endogenous pattern of trade dictated by comparative advantage. We derive an intuitive expression linking sectoral employment shares to sectoral expenditure shares and to sectoral net export shares of total GDP. Changes in productivity and in trade barriers affect expenditure and net export shares, and thus, employment shares, across sectors. We show how these driving forces can generate the "hump" pattern that characterizes the manufacturing employment share as a country develops, even when manufacturing is the sector with the highest productivity growth.structural transformation, international trade, sectoral labor reallocation

Sampling Artifact in Volume Weighted Velocity Measurement.--- II. Detection in simulations and comparison with theoretical modelling

Measuring the volume weighted velocity power spectrum suffers from a severe systematic error, due to imperfect sampling of the velocity field from inhomogeneous distribution of dark matter particles/halos in simulations or galaxies with velocity measurement. This "sampling artifact" depends on both the mean particle number density $\bar{n}_P$ and the intrinsic large scale structure (LSS) fluctuation in the particle distribution. (1) We report robust detection of this sampling artifact in N-body simulations. It causes $\sim 12$% underestimation of the velocity power spectrum at $k=0.1$h/Mpc for samples with $\bar{n}_P=6\times10^{-3}$ (Mpc/h)$^{-3}$. This systematic underestimation increases with decreasing $\bar{n}_P$ and increasing $k$. Its dependence on the intrinsic LSS fluctuations is also robustly detected. (2) All these findings are expected by our theoretical modelling in paper I \cite{Zhang14}. In particular, the leading order theoretical approximation agrees quantitatively well with simulation result for $\bar{n}_P\gtrsim6\times 10^{-4}$(Mpc/h)$^{-3}$. Furthermore, we provide an ansatz to take high order terms into account. It improves the model accuracy to $\lesssim1$% at $k\lesssim0.1$h/Mpc over 3 orders of magnitude in $\bar{n}_P$ and over typical LSS clustering from $z=0$ to $z=2$. (3) The sampling artifact is determined by the deflection ${\bf D}$ field, which is straightforwardly available in both simulations and data of galaxy velocity. Hence the sampling artifact in the velocity power spectrum measurement can be self-calibrated within our framework. By applying such self-calibration in simulations, it becomes promising to determine the {\it real} large scale velocity bias of $10^{13}M_\odot$ halos with $\sim 1$% accuracy, and that of lower mass halos by better accuracy. ...[abridged]Comment: 11 pages, 11 figures. More arguments added, match the PRD accepted versio

Structural change in an open economy

We develop a tractable, three-sector model to study structural change in a two-country world. The model features an endogenous pattern of trade dictated by comparative advantage. We derive an intuitive expression linking sectoral employment shares to sectoral expenditure shares and to sectoral net export shares of total GDP. Changes in productivity and in trade barriers affect expenditure and net export shares, and thus, employment shares, across sectors. We show how these driving forces can generate the "hump" pattern that characterizes the manufacturing employment share as a country develops, even when manufacturing is the sector with the highest productivity growth.

PHASE TRANSITION AND THERMODYNAMIC PROPERTIES STUDY OF ZIRCONIA USING FIRST PRINCIPLES METHOD

Zirconium dioxide (ZrO2) ceramics are of highly scientific and industrial interest. Since zirconia performs high melting temperature and small thermal conductivity, this material is well developed and commonly used for thermal barrier coating material in industry. This study investigates zirconium dioxide properties based on first principles calculation. Structural properties, including band structure, density of state, lattice parameter, as well as elastic constant for both monoclinic and tetragonal zirconia were computed. Pressure based phase transition of tetragonal zirconia (t-ZrO2) was calculated using DFT method CASTEP code. This work is based on band structure and tetragonal distortion change under compression pressure. The results predict a transition from monoclinic structure to a fluorite-type cubic structure at pressure of 37 GPa. Monoclinic phased zirconia (m-ZrO2) thermodynamic property calculations were also carried out using the Vienna ab initio Simulation Package VASP coupled with PHONOPY. The temperature dependence of specific heat capacity, entropy, free energy, Debye temperature of monoclinic zirconia, from 0 to 1000K, were computed and compared well with those reported from other relevant work

Finite Element Simulation and Experimental Validation of Distortion and Cracking Failure Phenomena in Direct Metal Laser Sintering Fabricated Component

A new one-way coupled thermal-mechanical finite element based model of direct metal laser sintering (DMLS) is developed to simulate the process, and predict distortion and cracking failure location in the fabricated components. The model takes into account the layer-by-layer additive manufacturing features, solidification and melting phenomena. The model is first validated using experimental data, then model is applied to a DMLS fabricated component. The study shows how the stress distribution at the support-solid interface is critical to contributing to cracking and distortion. During the DMLS process, thermal stress at the support-solid interface reaches its maximum during the printing process, particularly when the first solid layer is built above the support layer. This result suggests that cracking at the interface may occur during the printing process, which is consistent with experimental observation. Using a design parametric study, a thick and low-density porous layer is found to reduce residual stress and distortion in the built component. The developed finite element model can be used to future design and optimize DMLS process

Sintering Mechanisms and Mechanical Properties of 3D Printed Metals

poster abstractNickel and iron based alloys are widely used as raw materials in 3D printing or additive manufacturing process. In direct metal laser sintering (DMLS) process, a primary 3D printing technique for metals, metallic powders are sintered to a desired shape by heat energy from a laser beam. This study presents a molecular dynamics study to simulate the sintering process and resultant mechanical properties of 3D printed metal parts. The model will elucidate and quantify the diffusion process during 3D printing of nickel and iron powders. Further, to study the mechanical properties of the sintered nickel parts, uniaxial tensile test simulations will be performed on the parts sintered at different heating rates. The calculated diffusion activation energy for nickel is 7.91 KJ/mole in the nickel particle core region; and 8.55 KJ/mole on the surface area, respectively, which agrees well with the experimentally measured data from literature. Uniaxial tensile test simulation results show that a higher heating rate will increase the mechanical strength of sintered material