Comparison of Density of Stainless Steel 316L Parts Produced with Selective Laser Melting using Different Powder Grades

Selective Laser Melting is a powder based additive manufacturing process where the metallic powder particles are fused to 3D parts using a high energy laser beam. Much work has already been conducted to investigate the details of the process, suitable materials and process parameters and further more. As metallic powders are the raw material for this process, there are still a lot of open questions relating to suitable grain size distributions for dense parts with regard to productivity, surface quality, mechanical strength and ductility. The present work shows the results of density measurements of parts, produced using three different particle size distributions and different energy densities of the laser beam. Two layer thicknesses of 30μm and 45μm were investigated. It is shown that without a minimal amount of fine grains, which are able to fill the voids between the coarse grains, lower scan speeds are needed in order to produce dense parts. Furthermore, the differences in the relation of the powders to the densities, the layer thicknesses and laser scan speeds indicate, that the powder grain size distribution plays an important role and that should be taken into account for optimal results. This work is a contribution to the ASTM initiative F42 for “Additive Manufacturing”.Mechanical Engineerin

Transport properties of clean and disordered superconductors in matrix field theory

A comprehensive field theory is developed for superconductors with quenched disorder. We first show that the matrix field theory, used previously to describe a disordered Fermi liquid and a disordered itinerant ferromagnet, also has a saddle-point solution that describes a disordered superconductor. A general gap equation is obtained. We then expand about the saddle point to Gaussian order to explicitly obtain the physical correlation functions. The ultrasonic attenuation, number density susceptibility, spin density susceptibility and the electrical conductivity are used as examples. Results in the clean limit and in the disordered case are discussed respectively. This formalism is expected to be a powerful tool to study the quantum phase transitions between the normal metal state and the superconductor state.Comment: 9 page

Power-law distributions and Levy-stable intermittent fluctuations in stochastic systems of many autocatalytic elements

A generic model of stochastic autocatalytic dynamics with many degrees of freedom $w_i$ $i=1,...,N$ is studied using computer simulations. The time evolution of the $w_i$'s combines a random multiplicative dynamics $w_i(t+1) = \lambda w_i(t)$ at the individual level with a global coupling through a constraint which does not allow the $w_i$'s to fall below a lower cutoff given by $c \cdot \bar w$, where $\bar w$ is their momentary average and $0<c<1$ is a constant. The dynamic variables $w_i$ are found to exhibit a power-law distribution of the form $p(w) \sim w^{-1-\alpha}$. The exponent $\alpha (c,N)$ is quite insensitive to the distribution $\Pi(\lambda)$ of the random factor $\lambda$, but it is non-universal, and increases monotonically as a function of $c$. The "thermodynamic" limit, N goes to infty and the limit of decoupled free multiplicative random walks c goes to 0, do not commute: $\alpha(0,N) = 0$ for any finite $N$ while $\alpha(c,\infty) \ge 1$ (which is the common range in empirical systems) for any positive $c$. The time evolution of ${\bar w (t)}$ exhibits intermittent fluctuations parametrized by a (truncated) L\'evy-stable distribution $L_{\alpha}(r)$ with the same index $\alpha$. This non-trivial relation between the distribution of the $w_i$'s at a given time and the temporal fluctuations of their average is examined and its relevance to empirical systems is discussed.Comment: 7 pages, 4 figure

Improving poverty reduction in Europe: what works best where?

This article examines how income poverty is affected by changes to the scale of tax-benefit policies and which are the most cost-effective policies in reducing poverty or limiting its increase in seven diverse EU countries. We do that by measuring the implications of increasing/reducing the scale of each policy instrument, using microsimulation methods while holding constant the policy design and national context. We consider commonly applied policy instruments with a direct effect on household income: child benefits, social assistance, income tax lower thresholds and a benchmark case of rescaling the whole tax-benefit system. We find that the assessment of the most cost-effective instrument may depend on the measure of poverty used and the direction and scale of the change. Nevertheless, our results indicate that the options that reduce poverty most cost-effectively in most countries are increasing child benefits and social assistance, while reducing the former is a particularly poverty-increasing way of making budgetary cuts

Castaing Instability and Precessing Domains in Confined Alkali Gases

We explore analogy between two-component quantum alkali gases and spin-polarized helium systems. Recent experiments in trapped gases are put into the frame of the existing theory for Castaing instability in transverse channel and formation of homogeneous precessing domains in spin-polarized systems. Analogous effects have already been observed in spin-polarized $$ and $^{3}He- ^{4}He$ mixtures systems. The threshold effect of the confining potential on the instability is analyzed. New experimental possibilities for observation of transverse instability in a trap are discussed.Comment: 6 RevTex pages, no figure

Singularities of Magnetic and Elastic Characteristics of La2/3Ba1/3MnO3: Analysis of Martensitic Kinetics

A coordinated temperature behavior of magnetic susceptibility and internal friction has been observed in the La2/3Ba1/3MnO3 manganite in the temperature region of the crystal phase separation 5-340 K. Stepwise temperature behavior of the susceptibility of the single crystal sample and corresponding singular behavior of the internal friction in the polycrystalline manganite have been found. These small-scale features of the temperature dependences of the susceptibility and the internal friction are considered to be a reflection of martensitic kinetics of the structural phase transformation R3c-Imma in the 200 K temperature region.Comment: 13 pages, 4 figures, Submitted J. Magn. Magn. Mate

Spin-Charge Separation in the t−Jt-J Model: Magnetic and Transport Anomalies

A real spin-charge separation scheme is found based on a saddle-point state of the $t-J$ model. In the one-dimensional (1D) case, such a saddle-point reproduces the correct asymptotic correlations at the strong-coupling fixed-point of the model. In the two-dimensional (2D) case, the transverse gauge field confining spinon and holon is shown to be gapped at {\em finite doping} so that a spin-charge deconfinement is obtained for its first time in 2D. The gap in the gauge fluctuation disappears at half-filling limit, where a long-range antiferromagnetic order is recovered at zero temperature and spinons become confined. The most interesting features of spin dynamics and transport are exhibited at finite doping where exotic {\em residual} couplings between spin and charge degrees of freedom lead to systematic anomalies with regard to a Fermi-liquid system. In spin dynamics, a commensurate antiferromagnetic fluctuation with a small, doping-dependent energy scale is found, which is characterized in momentum space by a Gaussian peak at ($\pi/a$, $\pi/a$) with a doping-dependent width ($\propto \sqrt{\delta}$, $\delta$ is the doping concentration). This commensurate magnetic fluctuation contributes a non-Korringa behavior for the NMR spin-lattice relaxation rate. There also exits a characteristic temperature scale below which a pseudogap behavior appears in the spin dynamics. Furthermore, an incommensurate magnetic fluctuation is also obtained at a {\em finite} energy regime. In transport, a strong short-range phase interference leads to an effective holon Lagrangian which can give rise to a series of interesting phenomena including linear-$T$ resistivity and $T^2$ Hall-angle. We discuss the striking similarities of these theoretical features with those found in the high-$T_c$ cuprates and give aComment: 70 pages, RevTex, hard copies of 7 figures available upon request; minor revisions in the text and references have been made; To be published in July 1 issue of Phys. Rev. B52, (1995

Inequality of opportunity in the land of opportunities : 1968-2001

We measure inequality of opportunity for earnings acquisition in the U.S. between 1968 and 2001. Following recent theories of social justice, earnings determinants are divided into two parts: Circumstances, which are characteristics outside individual control and effort representing factors impacting earnings but under individuals’ responsibility. Equality of opportunity requires that inequality of circumstances must be corrected while differences of effort must remain unaltered. Circumstances are represented by parental education and occupation, ethnic origin, place of birth and age. Effort is modeled with schooling choices and labour supply decisions. Using the PSID from 1968 to 2001, we provide two alternative assessments of inequality of opportunity using counterfactual distributions. The statistical framework is semi-parametric and builds on duration models. Finally, we conclude that inequality of opportunity represents between 20 and 43% of earnings inequality, but decreases all over the period reaching around 18% in 2001