Support Generation for Fused Deposition Modeling

With the growth of the use of Rapid Prototyping (RP) systems, there has been a corresponding growth in the complexity of parts expected from the various RP processes. To meet the demand for increasingly more intricate and detailed prototypes, the technology has matured and improved, allowing RP users to build these parts faster, better and with a variety of materials. Stratasys Inc.'s Fused Deposition Modeling (FDM ®) system is one of the leading prototyping systems available in the market today. Recent enhancements in electro-mechanical control of the machine head have improved the viability of FDM as a system for manufacturing complex prototypes. The FDM-1600 system can now also create detailed parts using ABS, a widely used plastic in the automotive and other industries. In addition, we have further reduced the lead time (preprocessing or operator time) in the product design cycle with the inclusion of an automatic support generation module in Stratasys' proprietary QuickSlice® software product. QuickSlice processes STL data to generate machine code to drive the FDM system.Mechanical Engineerin

Patterning of chemical gradients with submicrometer resolution using edge-spreading lithography

Peer reviewed: YesNRC publication: Ye

Point-contact Andreev-reflection spectroscopy in ReFeAsO_{1-x}F_x (Re = La, Sm): Possible evidence for two nodeless gaps

A deep understanding of the character of superconductivity in the recently discovered Fe-based oxypnictides ReFeAsO1-xFx (Re = rare-earth) necessarily requires the determination of the number of the gaps and their symmetry in k space, which are fundamental ingredients of any model for the pairing mechanism in these new superconductors. In the present paper, we show that point-contact Andreev-reflection experiments performed on LaFeAsO1-xFx (La-1111) polycrystals with Tc ~ 27 K and SmFeAsO0.8F0.2 (Sm-1111) ones with Tc ~ 53 K gave differential conductance curves exhibiting two peaks at low bias and two additional structures (peaks or shoulders) at higher bias, an experimental situation quite similar to that observed by the same technique in pure and doped MgB2. The single-band Blonder-Tinkham-Klapwijk model is totally unable to properly fit the conductance curves, while the two-gap one accounts remarkably well for the shape of the whole experimental dI/dV vs. V curves. These results give direct evidence of two nodeless gaps in the superconducting state of ReFeAsO1-xFx (Re = La, Sm): a small gap, Delta1, smaller than the BCS value (2Delta1/kBTc ~ 2.2 - 3.2) and a much larger gap Delta2 which gives a ratio 2Delta2/kBTc ~ 6.5 - 9. In Sm-1111 both gaps close at the same temperature, very similar to the bulk Tc, and follow a BCS-like behaviour, while in La-1111 the situation is more complex, the temperature dependence of the gaps showing remarkable deviations from the BCS behaviour at T close to Tc. The normal-state conductance reproducibly shows an unusual, but different, shape in La-1111 and Sm-1111 with a depression or a hump at zero bias, respectively. These structures survive up to T* ~ 140 K, close to the temperatures at which structural and magnetic transitions occur in the parent, undoped compound.Comment: 10 pages, 7 color figures, Special Issue of Physica C on Superconducting Pnictide

Effect of transport-induced charge inhomogeneity on point-contact Andreev reflection spectra at ferromagnet-superconductor interfaces

We investigate the transport properties of a ferromagnet-superconductor interface within the framework of a modified three-dimensional Blonder-Tinkham-Klapwijk formalism. In particular, we propose that charge inhomogeneity forms via two unique transport mechanisms, namely, evanescent Andreev reflection and evanescent quasiparticle transmission. Furthermore, we take into account the influence of charge inhomogeneity on the interfacial barrier potential and calculate the conductance as a function of bias voltage. Point-contact Andreev reflection (PCAR) spectra often show dip structures, large zero-bias conductance enhancement, and additional zero-bias conductance peak. Our results indicate that transport-induced charge inhomogeneity could be a source of all these anomalous characteristics of the PCAR spectra.Comment: 9 pages, 6 figure

New considerations on the validity of the Wiener-Granger causality test

The Wiener-Granger causality test is used to predict future experimental results from past observations in a purely mathematical way. For instance, in many scientific papers this test has been used to study the causality relations in the case of neuronal activities. Albeit some papers reported repeatedly about problems or open questions related to the application of the Granger causality test on biological systems, these criticisms were always related to some kind of assumptions to be made before the test's application. In our paper instead we investigate the Granger method itself, making use exclusively of fundamental mathematical tools like Fourier transformation and differential calculus. We find that the ARMA method reconstructs any time series from any time series, regardless of their properties, and that the quality of the reconstruction is given by the properties of the Fourier transform. In literature several definitions of "causality" have been proposed in order to maintain the idea that the Granger test might be able to predict future events and prove causality between time series. We find instead that not even the most fundamental requirement underlying any possible definition of causality is met by the Granger causality test. No matter of the details, any definition of causality should refer to the prediction of the future from the past; instead by inverting the time series we find that Granger also allows one to "predict"the past from the future