Causes Of Variation In Performance Research Articles

Process-Structure-Property Relationships of Laser Powder Bed Fusion Lattice Structures

Abstract Lattice structure metamaterials offer a variety of unique and tailorable properties, yet industrial adoption is slowed by manufacturability and inspection-related difficulties. Despite recent advances in laser powder bed fusion additive manufacturing, the sub-millimeter features of lattices are at the edge of process capabilities and suffer from low geometric quality. To better understand their complex process-structure-property (PSP) relationships, octahedron structures were manufactured across a power spectrum, inspected, and mechanically tested. X-ray computed tomography was used to characterize lattice geometry, and demonstrated that lattice strut geometry measures, increased significantly as a function of laser power. Furthermore, lattices are shown to exhibit a direct correlation between laser power and mechanical performance metrics. Performance variations up to 60% are shown as a function of process parameters despite nominally identical geometry. Significant geometry variations are found to be the cause of performance variation, while material properties as measured by microindentation hardness are constant across the studied parameter range. PSP relationships are modeled, and the limitations of these models are explored. It was found that resulting models can predict mechanical performance based on geometric characteristics with R2 values of up to 0.86. Finally, mechanistic causes of observed performance changes are discussed.

Experimental and Computational Investigation of Shaped Film Cooling Holes Designed to Minimize Inlet Separation

Abstract Film cooling is used to protect turbine components from the extreme temperatures by ejecting coolant through arrays of holes to create an air buffer from the hot combustion gases. Limitations in traditional machining meant film cooling holes universally have sharp inlets, which create separation regions at the hole entrance. The present study uses experimental and computational data to show that these inlet separation are a major cause of performance variation in crossflow fed film cooling holes. Three-hole designs were experimentally tested by independently varying the coolant velocity ratio (VR) and the coolant channel velocity ratio (VRc) to isolate the effects of crossflow on hole performance. Leveraging additive manufacturing (AM) technologies, the addition of a 0.25D radius fillet to the inlet of a 7-7-7 shaped hole is shown to significantly improve diffuser usage and significantly reduce variation in performance with VRc. A second AM design used a very large radius of curvature inlet to reduce biasing caused by the inlet crossflow. Experiments showed that this “swept” hole design did minimize biasing of the coolant flow to one side of the shaped hole, and it significantly reduced variations due to varying VRc. RANS simulations at six VR and three VRc conditions were made for each geometry to better understand how the new geometries changed the velocity field within the hole. The sharp and rounded inlets were seen to have very similar tangential velocity fields and jet biasing. Both AM inlets created more uniform, slower velocity fields entering the diffuser. The results of this article indicate that large improvements in film cooling performance can be found by leveraging AM technology.

Factors Affecting the Performance of Female Entrepreneurship: Evidence from Punjab, Pakistan

This study aims to present micro level perspective and analysis on gender related challenges on the performance of the female entrepreneurs in Punjab, Pakistan. It examines structural and cultural factors affecting women entrepreneurs and how specific women, interviewed in selected cities, perceive and respond to these. The research helps to identify both human and social capital factors affecting the performance of the female entrepreneurs. Furthermore, it explores the main causes of performance variations among the businesses owned by female entrepreneurs. Data analyses shows that women entrepreneur’s personal resources (Human and social capital) have an important role in their business progress.

The neural correlates of BCI performance variations in ALS: a pilot study

Event Abstract Back to Event The neural correlates of BCI performance variations in ALS: a pilot study Moritz Grosse-Wentrup1* 1 Max Planck Institute for Intelligent Systems, Empirical Inference, Germany Brain-Computer Interfaces (BCIs) hold the promise of enabling completely locked-in subjects, e.g., those in late stages of amyotrophic lateral sclerosis (ALS), to communicate by pure thought. To date, this promise has not been fulfilled. While healthy subjects and subjects in early to middle stages of ALS can learn how to operate a non-invasive BCI (Grosse-Wentrup et al., IEEE Transactions on Biomedical Engineering 56(4), 2009; Kübler et al., Neurology (64), 2005), no successful communication with a completely locked-in patient has been reported in literature. We believe that in order to enable completely locked-in patients to operate a BCI, we first need to understand the neuro-physiological causes of good and bad BCI performance. These insights might then be used induce a state-of-mind that is beneficial for operating a BCI, e.g., by neuro-feedback or electrical stimulation. In a series of recent studies, we have investigated the neuro-physiological causes of performance variations in healthy subjects operating a binary motor-imagery BCI. We found that gamma-range oscillations (between 55-85 Hz) modulate the sensorimotor-rhythm (Grosse-Wentrup et al., NeuroImage 56(2), 2011), resulting in group-average decoding differences of up to 22.2% depending on the state of fronto-parietal gamma-power (Grosse-Wentrup, 5th IEEE/EMBS International Conference on Neural Engineering, 2011). Here, we report results of a pilot study that reproduces this effect in one ALS patient. We recorded a 128-channel EEG in an ALS patient performing motor-imagery of the left or right hand. The patient was artificially ventilated, with residual control of the right wrist. We trained a support vector machine in classifying left- vs. right hand motor imagery, based on bandpower features over sensorimotor-areas. This resulted in a cross-validated accuracy of 59.2%, which is sufficient to reject the null-hypothesis of chance-level performance with p = 0.0178 (N=120). To identify brain areas related to BCI-performance, we first performed an Independent Component Analysis, manually rejected independent components (ICs) representing artifactual muscle activity, and then correlated gamma-power of the remaining ICs with a trial-wise measure of motor-imagery performance (cf. Grosse-Wentrup et al. (2011) for a description of this performance measure). In this way, we identified two ICs whose gamma-power exhibited a strong negative correlation with BCI-performance (rho = -0.3161/-0.2888, p = 0.0180/0.0258 (corrected for multiple comparisons), N = 120). A subsequent source localization procedure identified the origin of these gamma-range oscillations in the right superior parietal lobule, consistent with our findings in healthy subjects. While it remains to be seen how consistently this effect can be reproduced in ALS, its investigation over the course of ALS progression may provide novel insights into the current failure of completely locked-in patients to communicate by means of a BCI. Keywords: Amyotrophic Lateral Sclerosis, Motor Imagery, Neurotechnology and brain-machine interface Conference: BC11 : Computational Neuroscience & Neurotechnology Bernstein Conference & Neurex Annual Meeting 2011, Freiburg, Germany, 4 Oct - 6 Oct, 2011. Presentation Type: Poster Topic: neurotechnology and brain-machine interface (please use "neurotechnology and brain-machine interface" as keyword) Citation: Grosse-Wentrup M (2011). The neural correlates of BCI performance variations in ALS: a pilot study. Front. Comput. Neurosci. Conference Abstract: BC11 : Computational Neuroscience & Neurotechnology Bernstein Conference & Neurex Annual Meeting 2011. doi: 10.3389/conf.fncom.2011.53.00117 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 23 Aug 2011; Published Online: 04 Oct 2011. * Correspondence: Dr. Moritz Grosse-Wentrup, Max Planck Institute for Intelligent Systems, Empirical Inference, Tübingen, 72076, Germany, moritz.grosse-wentrup@tuebingen.mpg.de Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Moritz Grosse-Wentrup Google Moritz Grosse-Wentrup Google Scholar Moritz Grosse-Wentrup PubMed Moritz Grosse-Wentrup Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

The role of structural defects and texture variability in the performance of poly-Si thin film transistors

High-performance poly-Si Thin Film Transistors (TFTs) with champion mobility and threshold voltage characteristics have been reported by several groups in the literature. Performance improvements have been especially spectacular after the wide acceptance of laser-based, lateral crystallization technology and its numerous variants. Despite the noted improvements in average transistor performance, variation in TFT characteristics still presents substantial difficulties to control. Speculation on the cause of the variation has been provided by various sources but, so far, no systematic study has been performed to that effect. In this work we have conducted an extensive study of characteristics of poly-Si TFTs, fabricated by laser crystallization, and their relationship to the microstructural details of the active layer. Our study clarifies the effect of a single grain boundary inclusion in the device channel and pinpoints the key causes of variation in performance even in the absence of “hard” boundaries. The existence of structural defects, as well as texture variation, is found to correlate well with the observed variability in TFT mobility and threshold voltage. These findings have also been confirmed by a simple quantitative model. Our work points to the importance in achieving consistent microstructure and the difficulty in doing so by employing blanket crystallization technologies. To that end, crystallization technology emphasizing location control appears to be preferable.

Performance sensitivity to system parameters in multiwavelength super-continuum sources

We determine the fundamental cause of performance variation as a function of system parameters, in supercontinuum (SC) sources in a normal-dispersive fiber, with high-order nonlinearity effects included. The variations in the sliced-pulse quality with respect to the soliton order N, the input peak power, the slicing filter bandwidth, as well as the optimization of the fiber length and the slicing wavelength, are numerically investigated. The results show that, at a constant average input power, narrower input pulses (or smaller N) can help achieve broader output spectrum but at the expense of degradation in the sliced-pulse quality. Better quality of the sliced pulses can be obtained by using a slicing filter with wider filter bandwidth. Besides, the input peak power is found to have significant impact on the choice of the suitable slicing wavelength. These results can facilitate the optimization of system parameters in designing SC sources for optical transmission applications.

Analysis of performance optimization in supercontinuum sources.

We have determined the cause of performance variation as a function of system parameters in supercontinuum (SC) sources in a normal-dispersion fiber by numerically analyzing the noise evolution of the SC. High-order nonlinearity was considered in such an analysis for the first time to our knowledge. We found that the evolution of noise along the SC fiber has two stages: First, the noise is governed by dispersion, which is different from that of the signal, whereas self-steeping leads to an asymmetric noise distribution across the spectrum. Second, four-wave mixing generates new noise components, whereas Raman scattering augments the asymmetry. We evaluated the qualities of the spectrally sliced pulses at several stages to verify the analysis and found an asymmetric profile of the sliced-pulses' quality versus frequency.