Description: This poster received 1st place in the 2013 Graduate Exhibition in the Engineering category. Abstract: High energy lasers emerged as an innovative and potential industrial tool to fabricate complex shapes on structural ceramics which is otherwise difficult using conventional machining techniques. However, obtaining a desired surface finish at higher material removal rate during laser machining of structural ceramics is still a critical issue. In this situation, the better understanding of various physical phenomena such as heat transfer, fluid flow, recoil pressure, Marangoni convection, and surface tension and its influence on the evolution of typical surface topography during laser machining could be more helpful. In light of this, this study was attempted to present the state of the art of laser machining of alumina using an integrated experimental and computational approach. A multistep computational model based on COMSOL™ Multiphysics was developed to study the effect of various physical phenomena on the generation of surface topography for various laser machining conditions. Furthermore, this process model can be used as a handy tool for the process engineers to configure the process variables (laser power, scanning speed, pulse rate, size of overlap) to obtain the specified quality characteristics. The surface topography of laser machined ...

Description: In this article, the authors report an atomistic simulation study of the behavior of nanocomposite materials that are formed by incorporating single-walled carbon nanotubes (SWCNTs), with three different diameters, and a multiwalled carbon nanotube (MWCNT) into a single-crystal nickel matrix. The interactions between carbon and nickel atoms are described by a modified embedded atom method potential. Mechanical properties of these nanocomposite materials are predicted by atomistic calculations and compared with that of fcc nickel and pristine CNTs. The authors' simulations predict that all Ni/CNT composites studied in this work are mechanically stable. Their elastic properties depend on the volume fraction and diameter of embedded CNTs. The single-crystal Young's modulus (E₁₁) of Ni/SWCNT composites exhibit a large increase in the direction of CNTs alignment compared to that of a single-crystal nickel. However, a moderate but gradual decrease is seen for E₂₂ and E₃₃ in the transverse directions with increase in CNT diameters. As a consequence, Ni/SWCNTs show a gradual decrease for the polycrystalline Young's, bulk and shear moduli with the increasing CNT diameters and volume fractions. These reductions, although moderate, suggest that enhancement of mechanical properties for polycrystalline Ni/SWCNT nanocomposites are not achievable at any CNT volume fraction. The Ni/MWCNT composite ...

Description: This articles discusses an analysis of multiple ignition sites, primary circuits, and burst phase delay distributions. All higher order central nervous systems exhibit spontaneous neural activity, though the purpose and mechanistic origin of such activity remains poorly understood. The authors quantitatively analyzed the ignition and spread of collective spontaneous electrophysiological activity in networks of cultured cortical neurons growing in microelectrode arrays. Leader neurons, which form a mono-synaptically connected primary circuit, and initiate a majority of network bursts were found to be a small subset of recorded neurons. Leader/follower firing delay times formed temporally stable positively skewed distributions. Blocking inhibitory synapses usually resulted in shorter delay times with reduced variance. These distributions are characterizations of general aspects of internal network dynamics and provide estimates of pair-wise synaptic distances. The resulting analysis produced specific quantitative constraints and insights into the activation patterns of collective neuronal activity in self-organized cortical networks, which may prove useful for models emulating spontaneously active systems.

Description: This article discusses the thermal annealing behavior of an oxide layer under silicon. High resolution Rutherford backscattering spectrometry and ion channeling have been employed to evaluate the crystallinity of the surface silicon layer in oxygen implanted silicon. The quality of the top surface layer was determined by measuring the minimum yields along 〈110〉 directions in channeling spectra. Single crystal (100) silicon was implanted with 300 keV O2+ to a dose of 1.06 X 10(18) O2+/cm2. Measurements of residual damage of the top layer were made after annealing the samples at 1150 ˚C for times ranging from 10 to 240 min in either Ar or N2. Under the implantation conditions used in this experiment, a uniform oxide layer 0.52 μm thick was buried under a top silicon layer 0.17 μm thick. The buried oxide layer has abrupt silicon to oxide interfaces. The highest quality silicon surface layer was produced after 3-h annealing in an Ar ambient. A lesser quality silicon surface layer was produced by annealing for shorter times or for equivalent times in N2 ambient.