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The use of additive manufacturing (AM) processes for industrial fabrication has grown rapidly over the last ten years. The most well-known AM technologies are fused deposition modelling and stereolithography techniques. One particular industry where 3D printing is advantageous over traditional fabrication techniques is within ceramic components due to its flexibility. To establish a new and improved level of print quality and reduce resource consumption in the 3D printing ceramics industry, there is a need for fast integrated, sub-surface and non-destructive inspection (NDI) with high resolution. Several techniques have already been developed for high-resolution NDI, such as X-ray computed tomography (XCT), but none of them are both fast, integrable, and non-destructive while allowing deep penetration with high resolution. In this study, we demonstrate sub-surface monitoring of 3D printed alumina parts to a depth of $\sim$0.7 mm in images of 400$\times$2048 pixels with a lateral resolution of 30$~\mu$m and depth (or axial) resolution of 7$~\mu$m . The results were achieved using mid-infrared optical coherence tomography (MIR OCT) based on a MIR supercontinuum laser with a 4$~\mu$m center wavelength. We find that it is possible to detect individual printed ceramic layers and track predefined defects through all four processing steps: green, preconditioned, debinded, and sintered. Our results also demonstrate how a defect in the green phase could affect the final product. Based on the understanding of how defects develop in maturing printed parts, we pave the way for NDI integration in AM, which can be combined with artificial intelligence and machine learning algorithms for automatic defect classification in volume production of a new standard of high quality ceramic components., Comment: 15 pages, 8 figures, paper

In this paper, we report the design and fabrication of a highly birefringent polarization-maintaining photonic crystal fiber (PM-PCF) made from chalcogenide glass, and its application to linearly-polarized supercontinuum (SC) generation in the mid-infrared region. The PM fiber was drawn using the casting method from As38Se62 glass which features a transmission window from 2 to 10 $\mu m$ and a high nonlinear index of 1.13.10$^{-17}$m$^{2}$W$^{-1}$. It has a zero-dispersion wavelength around 4.5 $\mu m$ and, at this wavelength, a large birefringence of 6.10$^{-4}$ and consequently strong polarization maintaining properties are expected. Using this fiber, we experimentally demonstrate supercontinuum generation spanning from 3.1-6.02 $\mu m$ and 3.33-5.78 $\mu m$ using femtosecond pumping at 4 $\mu m$ and 4.53 $\mu m$, respectively. We further investigate the supercontinuum bandwidth versus the input pump polarization angle and we show very good agreement with numerical simulations of the two-polarization model based on two coupled generalized nonlinear Schr\"odinger equations., Comment: 13 pages, 8 figures

A fluorescence decay of high-affinity non-ratiometric Ca2+ indicator Oregon Green BAPTA-1 (OGB-1) is analyzed with unprecedented temporal resolution in the two-photon excitation regime. A triple exponential decay is shown to best fit the fluorescence dynamics of OGB-1. We provide a new model for accurate measurements of the free Ca2+ concentration and dissociation constants of non-ratiometric calcium indicators., Comment: 3 pages, 2 figures, figures revised, added chi-square goodness of fit

A system for time-correlated single photon counting applications based on CMOS single photon avalanche diodes is presented. An instrument response function of 79 ps allows a fluorescence decay of high-affinity Ca2+ indicator Oregon Green BAPTA-1 to be analyzed with unprecedented temporal resolution in the two-photon excitation regime. A triple exponential decay model is shown to best fit the fluorescence dynamics of OGB-1., Comment: 9 pages, 4 figures

Lattice formulation of a fermionic field theory defined on a randomly triangulated compact manifold is discussed, with emphasis on the topological problem of defining spin structures on the manifold. An explicit construction is presented for the two-dimensional case and its relation with the Ising model is discussed. Furthermore, an exact realization of the Kramers-Wannier duality for the two-dimensional Ising model on the manifold is considered. The global properties of the field are discussed. The importance of the GSO projection is stressed. This projection has to be performed for the duality to hold., Comment: Presented at the 41th Zakopane School of Theoretical Physics, 49 pages, Latex + 22 eps figures

We implement fermions on dynamical random triangulation and determine numerically the spectrum of the Dirac-Wilson operator D for the system of Majorana fermions coupled to two-dimensional Euclidean quantum gravity. We study the dependence of the spectrum of the operator (epsilon D) on the hopping parameter. We find that the distributions of the lowest eigenvalues become discrete when the hopping parameter approaches the value 1/sqrt{3}. We show that this phenomenon is related to the behavior of the system in the 'antiferromagnetic' phase of the corresponding Ising model. Using finite size analysis we determine critical exponents controlling the scaling of the lowest eigenvalue of the spectrum including the Hausdorff dimension d_H and the exponent kappa which tells us how fast the pseudo-critical value of the hopping parameter approaches its infinite volume limit., Comment: 26 pages, Latex + 23 eps figs, extended analysis of the spectrum, added figures