Overview of finite elements simulation of temperature profile to estimate properties of materials 3D-printed by laser powder-bed fusion

Laser powder bed fusion(LPBF),like many other additive manufacturing techniques,offers flexibility in design expected to become a disruption to the manufacturing industry.The current cost of LPBF process does not favor a try-anderror way of research,which makes modelling and simulation a field of superior importance in that area of engineering.In this work,various methods used to overcome challenges in modeling at different levels of approximation of LPBF process are reviewed.Recent efforts made towards a reliable and computationally effective model to simulate LPBF process using finite element(FE)codes are presented.A combination of ray-tracing technique,the solution of the radiation transfer equation and absorption measurements has been used to establish an analytical equation,which gives a more accurate approximation of laser energy deposition in powder-substrate configuration.When this new analytical energy deposition model is used in in FE simulation,with other physics carefully set,it enables us to get reliable cooling curves and melt track morphology that agree well with experimental observations.The use of more computationally effective approximation,without explicit topological changes,allows to simulate wider geometries and longer scanning time leading to many applications in real engineering world.Different applications are herein presented including:prediction of printing quality through the simulated overlapping of consecutive melt tracks,simulation of LPBF of a mixture of materials and estimation of martensite inclusion in printed steel.     

Improved detection of time windows of brain responses in fMRI using modified temporal clustering analysis

Temporal clustering analysis (TCA) has been proposed recently as a method to detect time windows of brain responses in functional MRI (fMRI) studies when the timing and location of the activation are completely unknown. Modifications to the TCA technique are introduced in this report to further improve the sensitivity in detecting brain activation. The modified TCA is based on the integrated signal intensity of a temporal cluster at each time point, while the original TCA is based only on the size of a temporal cluster at each time point. A temporal cluster at each time point is defined, in both TCA methods, as a group of pixels reaching their maximum (or minimum) values at the same time. Both computer simulation and in vivo fMRI experiments have been performed. Compared with the original TCA, the modified TCA shows a significant improvement in the sensitivity to detect activation peaks for determining time windows of brain responses.     

Iterative temporal clustering analysis for the detection of multiple response peaks in fMRI

The temporal clustering analysis (TCA) is a novel and effective technique for obtaining brain activation maps when the timing and location of the activation are completely unknown. Performing the TCA method once can only detect the largest peak of the activation time windows well, if multiple response peaks at the same location of the brain occur. However, this limitation can be removed by using a TCA method in an iterative way in order for the smaller peaks to be detected. Our in vivo fMRI experiments with event-related visual tasks have demonstrated this ability.     

A weakly compressible MPS method for modeling of open‐boundary free‐surface flow

A mesh‐free particle method, based on the moving particle semi‐implicit (MPS) interaction model, has been developed for the simulation of two‐dimensional open‐boundary free‐surface flows. The incompressibility model in the original MPS has been replaced with a weakly incompressible model. The effect of this replacement on the efficiency and accuracy of the model has been investigated. The new inflow–outflow boundary conditions along with the particle recycling strategy proposed in this study extend the application of the model to open‐boundary problems. The final model is able to simulate open‐boundary free surface flow in cases of large deformation and fragmentation of free surface. The models and proposed algorithms have been validated and applied to sample problems. The results confirm the model's efficiency and accuracy. Copyright © 2009 John Wiley & Sons, Ltd.     

A general,efficient, and inexpensive catalyst system for the coupling of aryl iodides and thiols

An efficient copper-catalyzed carbon-sulfur bond formation reaction was developed. This method is particularly noteworthy given its experimental simplicity, high generality, and exceptional level of functional group toleration and the low cost of the catalyst system. [reaction: see text]     

Observation of a very large internal hyperfine field (62.4 T) in the ferromagnetically ordered state of the S = 1 alpha-iron(II) octaethyltetraazaporphyrin

The origins of the extraordinarily large internal hyperfine field (62.4 T) for the three-dimensional (weak) ferromagnetically ordered ground state of alpha-Fe(OETAP) are discussed semiquantitatively in terms of existing physical theory. In particular, the classical Fermi-contact contribution to the internal field is found to be highly enhanced by a very large orbital contribution and a significant dipolar term of the same sign. A rationale for the unexpected ordering of this S = 1 non-Kramers system is also presented.     

An algorithm for optimal minimax routing in ATM networks

Asynchronous Transfer Mode (ATM) has been adopted by the CCITT as the transport mode in which Broadband ISDN will be based. In this paper, we formulate the problem of routing cells in an ATM network as an optimization problem. The objective is to minimize the largest cell loss probability among all links. The constraints correspond to a multicommodity network flow problem with gains. An algorithm to determine a global optimal flow assignment is presented. The minimax routing algorithm was implemented and tested on several sample networks. The computational experiments show that the algorithm is computationally efficient.Supported by NSF grant NCR 92-23148.     

Characterization of the structure and organization of β-form crystals in type III and type IV isotactic polypropylene spherulites

Anisotropic growth of β-form crystals of isotactic polypropylene in type III and type IV spherulites has made possible microanalysis of the unit cell structure, optical properties, and crystal arrangement within the spherulites. Micro x-ray studies of the type III and type IV spherulites show that interspherulitic β-form crystals have a hexagonal unit cell with dimensions; a = 19.08 Å and c = 6.49 Å. The intrinsic refractive indices of these β-form crystals are 1.506 along the a axis and 1.536 along the c axis. The organization of the crystals within the spherulites and the optical properties of the spherulites are also quantitatively evaluated. Both the type III and type IV spherulites have the a axis of the crystal radial while the crystals rotate randomly around the type III spherulite radii and periodically around the type IV spherulite radii. The radial refractive index for both the type III and type IV spherulites has the same value of 1.496. The tangential refractive index of the type III spherulite has a constant value of 1.509; it varies periodically between a minimum of 1.496 and a maximum of 1.519 in the type IV spherulite. Microtechniques such as micro x-ray diffraction, interference microscopy, birefringence, and optical microscopy were required for acquisition of the data.     

ToF atom-probe fim study of LaB6 single crystals

The field evaporation mass spectra of LaB₆ are obtained with time-of-flight atom-probe field ion microscope in vacuum and in the presence of hydrogen, nitrogen and oxygen. The spectra are consistent with a preferential chemisorption of these gases on boron sites.