24 research outputs found
Cerebellar output controls generalized spike-and-wave discharge occurence
© 2015 The Authors Annals of Neurology published by Wiley Periodicals, Inc. on behalf of American Neurological Association. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License (CC BY-NC-ND 4.0) which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.Disrupting thalamocortical activity patterns has proven to be a promising approach to stop generalized spike-and-wave discharges (GSWDs) characteristic of absence seizures. Here, we investigated to what extent modulation of neuronal firing in cerebellar nuclei (CN), which are anatomically in an advantageous position to disrupt cortical oscillations through their innervation of a wide variety of thalamic nuclei, is effective in controlling absence seizuresPeer reviewedFinal Published versio
Influence of Nd : YAG parameters on the selective laser sintering of metallic powders
Compared with CW CO2 laser sources, Nd:YAG lasers with Q-switching capability offer a wider parameter range, with improved sintering control, due to the short pulsed energy delivery. In particular, thermal diffusion being strictly limited by the nanosecond interaction between the energy pulse and the powder, higher accuracy can be achieved, while caking can be minimized. By systematically varying average power, scan velocity and repetition rate, process maps are established, for various materials, such as nickel and cobalt alloys, and titanium. Sintering depth and macrostructures are determined for different parameter sets. Basic models and physical explanations are given, for the various phenomena and consolidation processes. This mapping provides a correlation between the process parameters and the structure and properties of the produced parts. Results show that roughness and density are related to the pulsed energy delivery. For example, it is shown that multi-layer Ti samples can be sintered to a density close to 80 %
Optimization of powder layer density in selective laser sintering
An important parameter for the overall quality of SLS parts is the density of powder layers before sintering. Previous studies have shown that the control of powder particle shape and size distribution can increase the density of non-packed powder beds. However, these studies concerned beds several orders of magnitude larger than the SLS layers. The purpose of this study is to determine if, and to what extent, the density of thin powder layers can be increased. Experiments show that the density of thin layers increases from 53% to 63% when adding 30% fine powder to the coarse powder, with a coarse-to-fine ratio of 1:10. Compared with the bulk experiments, this density improvement method is less efficient, because the particles do not arrange as efficiently, and the wall effects can become predominant
Thermal behavior of parts made by direct metal laser sintering
The Direct Metal Laser Sintering (DMLS) manufacturing technique induces thermal stresses in parts. When such parts are used at elevated temperatures, residual stresses are relaxed and the part can suffer significant distortion. This study presents values of geometrical distortion for two laser exposure strategies and for different heat treatment temperatures and durations, Surface and bulk hardness data are provided as well as porosity measurements. At temperatures above 300 degrees C, the geometrical changes become important. A stabilization treatment at 600 degrees C can help reduce distortions
Direct rapid tooling: a review of current research
Rapid prototyping technologies are now evolving toward rapid tooling. The reasons for this extension are found in the need to further reduce the time-to-market by shortening not only the development phase, but also the industrialization phase of the manufacturing process. The present state of rapid tooling is reviewed and the direct rapid tooling concept, aimed at developing direct and rapid tool manufacturing processes, is presented, along with three promising methods. Their intrinsic properties are outlined and compared. Necessary research and development are described in terms of direct rapid tooling requirements
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Thermal Behavior of Parts Made by Direct Metal Laser Sintering
The Direct Metal Laser Sintering (DMLS) manufacturing technique induces thermal stresses
in parts. When such parts are used at elevated temperatures, residual stresses are relaxed and the
part can suffer significant distortion. This study presents values of geometrical distortion for two
laser exposure strategies and for different heat treatment temperatures and durations. Surface and
bulk hardness data are provided as well as porosity measurements. At temperatures above 300
the geometrical changes become important. A stabilization treatment. at 600°C can help reduce
distortions.Mechanical Engineerin
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Injection Molds Behavior and Lifetime Characterization
This paper presents the concept of a standard method used to determine the durability of
injection molds. In particular, some Rapid Tooling molds are less resistant to abrasive plastics than
conventional steel molds. Some evidence of wear in a conventional mold is given, and a specific
mold is designed for this test; polymer materials are defined and the test methodology is outlined.
Numerical simulation is utilized to show the areas ofthe mold subject to high shear stresses.Mechanical Engineerin
Injection molds behavior and lifetime characterization - Concept and design of a standard measurement method
This paper presents the concept of a standard method used to determine the durability of injection molds. In particular, some Rapid Tooling molds are less resistant to abrasive plastics than conventional steel molds. Some evidence of wear in a conventional mold is given, and a specific mold is designed for this test; polymer materials are defined and the test methodology is outlined. Numerical simulation is utilized to show the areas of the mold subject to high shear stresses