On the role of microstructural variability in pultrusion

Pultrusion is a continuous manufacturing method to produce composite parts with constant cross sectional shape. This thesis focuses on advancing this manufacturing method by investigating the role of microstructural variability in pultrusion. The principal objective is to develop efficient numerical and experimental tools to improve the product quality of pultruded parts, taking meso/microstructural variability into account. To fulfill this objective, various numerical and experimental tools, which vary from material characterization to numerical process models and experimental validation techniques, were developed.Firstly, the focus is on understanding the behavior of pultrusion specific resin systems through the development of thermo-chemical mechanical material models. These models provide a comprehensive view of how resin properties evolve during the pultrusion process, a crucial step in ensuring high-quality end products. Then, the microstructural evolution with the compaction of rovings and the corresponding permeability of these materials are investigated. The fiber distribution analysis shows a reformation of fibers in parallel with the compaction direction. The apparent transverse permeability is shown to be lower than the permeability for the uniform distribution assumption. This investigation sheds light on the intricate relationship between meso/microstructure and impregnation, vital for preventing process-induced defects like voids and dry spots.As the thesis progresses, the emphasis shifts to residual stresses, a key concern in pultrusion. Novel numerical models are created to predict the distribution of mesoscale residual stresses, considering the local variation in fiber volume fraction (Vf). This contributes to a better understanding of how variability in fiber distribution influences residual stress formation and, consequently, part quality and performance. The experimental validation aspect of the research comes into play in the measurement of transverse residual stresses within thick pultruded parts. The local transverse residual stress in the core of a pultruded part is analyzed formerly with an assumption of uniform fiber distribution. The tensile transverse residual stress prediction in the literature is experimentally confirmed. This data and the method itself provide valuable insights into the real-world implications of residual stresses and their impact on the structural integrity of pultruded products. Later, a novel part of the thesis lies in the characterization of transverse residual stress states while considering non-uniform fiber distribution. This analysis offers a comprehensive view of how variability affects residual stresses, facilitating a better understanding of the pultrusion process.The discussion section critically reviews the contributions of each chapter, emphasizing their roles in improving pultruded product quality. It explores how variations in materials and the manufacturing process affect product quality, highlighting the reduction of defects and controlled residual stress distribution. This section also outlines future steps for advancing pultrusion technology and product quality.In summary, this thesis represents some essential steps to reach a holistic approach to advance the field of pultrusion by enhancing our understanding of the interplay between processing, meso/microstructure, and material properties. By addressing the challenges of variability and residual stresses, this research ultimately contributes to the production of higher-quality pultruded parts

Investigation of transverse residual stresses in a thick pultruded composite using digital image correlation with hole drilling

© 2019 Elsevier Ltd Process induced residual stresses are one of the main sources of defects such as (pre) mature matrix cracking during pultrusion of fiber reinforced polymer composite profiles. Recently, comprehensive process models have been developed to understand and describe the underlying mechanisms of the residual stresses in pultrusion processes. The predicted stresses however have not been validated with experimental measurements which are necessary to verify the implemented material models and assumptions in the process models. A hole drilling method with digital image correlation (DIC) is used in the present work to measure the transverse strain relaxation due to material removal in a pultruded thick composite profile (20 × 20 mm) made of unidirectional glass/polyester. The corresponding residual stress state is back calculated using the measured strains in a finite element based numerical model. The estimated level of transverse residual stress in the core of the profile was found to be 6.1 MPa in tension

An Experimental Study of Reduced-Voltage Operation in Modern FPGAs for Neural Network Acceleration

We empirically evaluate an undervolting technique, i.e., underscaling the circuit supply voltage below the nominal level, to improve the power-efficiency of Convolutional Neural Network (CNN) accelerators mapped to Field Programmable Gate Arrays (FPGAs). Undervolting below a safe voltage level can lead to timing faults due to excessive circuit latency increase. We evaluate the reliability-power trade-off for such accelerators. Specifically, we experimentally study the reduced-voltage operation of multiple components of real FPGAs, characterize the corresponding reliability behavior of CNN accelerators, propose techniques to minimize the drawbacks of reduced-voltage operation, and combine undervolting with architectural CNN optimization techniques, i.e., quantization and pruning. We investigate the effect of environmental temperature on the reliability-power trade-off of such accelerators. We perform experiments on three identical samples of modern Xilinx ZCU102 FPGA platforms with five state-of-the-art image classification CNN benchmarks. This approach allows us to study the effects of our undervolting technique for both software and hardware variability. We achieve more than 3X power-efficiency (GOPs/W) gain via undervolting. 2.6X of this gain is the result of eliminating the voltage guardband region, i.e., the safe voltage region below the nominal level that is set by FPGA vendor to ensure correct functionality in worst-case environmental and circuit conditions. 43% of the power-efficiency gain is due to further undervolting below the guardband, which comes at the cost of accuracy loss in the CNN accelerator. We evaluate an effective frequency underscaling technique that prevents this accuracy loss, and find that it reduces the power-efficiency gain from 43% to 25%.Comment: To appear at the DSN 2020 conferenc

Jeden z gigantów neurochirurgii odszedł od nas ponad dekadę temu, a w literaturze neurochirurgicznej nie poświęcono mu większej uwagi

One of the giants of neurological surgery left us over a decade ago. Charles George Drake died September 15, 1998 in London, Ontario after an extended bout with lung cancer. Although he will always be identified with taking posterior fossa aneurysm surgery from the realm of the daring to the domain of the routine, his contributions were much broader. Clinical neurosciences have been blessed in the past century by the life and works of Drake. In the neurosurgical world, the achievements of Drake are very well known and have been well recorded. Unfortunately, in the past decade since his passing, only one paper has been published about him and his contributions to neurosurgery. This is a historical paper regarding Charles George Drake that attempts to (1) remember Drake as a pioneer; (2) to evaluate lessons that we have learned from him; and (3) to address the question ‘What made him great?’. As per Drake's teachings, this paper is meant to articulate the unique perspectives Charlie provided with respect to how we learn our craft, maintain the integrity of reporting, and implement suggestions as to how we may progress into the future. In conclusion, it is our hope that this paper will bring to life the unique character of Drake and his unprecedented blend of genius, creativity, technical skill, introspection, and ever-present humility for all international neurosurgeons to appreciate.Charles George Drake, jeden z gigantów neurochirurgii, zmarł przed ponad 10 laty. Chociaż jego nazwisko będzie zawsze kojarzone z wprowadzeniem do praktyki chirurgicznego leczenia tętniaków tylnego dołu czaszki, wkład Drake'a w neurochirurgię jest znacznie szerszy. Niestety, w ciągu dekady od jego odejścia opublikowano tylko jeden artykuł poświęcony jego życiu i wkładowi w neurochirurgię. Niniejszy historyczny artykuł dotyczący Charlesa George'a Drake'a podejmuje próbę upamiętnienia go jako pioniera, poddania ocenie pozostawionej przez niego spuścizny i odpowiedzi na pytanie, co uczyniło go wielkim. Mamy nadzieję, że artykuł ten przybliży środowisku neurochirurgów wyjątkowy charakter Drake'a i cechujące go bezprzykładne połączenie geniuszu, kreatywności, sprawności technicznej, wglądu i nieodłącznej skromności

Meso-Scale Process Modelling Strategies for Pultrusion of Unidirectional Profiles

The resin injection pultrusion is an automated composite manufacturing method in which the resin is injected in a chamber. The flow and the thermo chemical mechanical (TCM) models have been studied for the pultrusion process to improve the reliability of the final products. Flow models are needed to understand and describe the fiber impregnation, filling time and presence of dry spots or voids. Also pressure field in the injection chamber can be estimated with flow models. TCM models are needed to predict residual stress distributions and to optimize the process conditions. A non-uniform fiber distribution strongly affects the results of both types of models. In this study, different strategies are carried out to implement non-uniform fiber distributions into the models. The cross-sectional image and fiber distribution of a 19×19 mm glass fiber reinforced polyester unidirectional pultruded composite is used. Non-uniform fiber distribution is observed and implemented into the flow model by means of permeability variations. The results of this study are compared with uniform fiber distribution results. In the TCM model, the non-uniform fiber volume content is implemented within different sized patches. The results show that the non-uniform fiber fraction should be taken into account for the process models of composites in order to capture the local process induced stresses and probability of dry spots or voids due to poor fiber impregnation

Echocardiographic evaluation of diastolic functions in patients with polycystic ovary syndrome: A comperative study of diastolic functions in sub-phenotypes of polycystic ovary syndrome

Background: Polycystic ovary syndrome (PCOS) is a heterogeneous endocrine disorder among reproductive-aged women. It is known to be associated with cardiovascular diseases. The aim of this study was to determine and compare the echocardiographic data of patients according to the phenotypes of PCOS. Methods: This study included 113 patients with PCOS and 52 controls. Patients were classified into four potential PCOS phenotypes. Laboratory analyses and echocardiographic measurements were performed. Left ventricular mass was calculated by using Devereux formula and was indexed to body surface area. Results: Phenotype-1 PCOS patients had significantly higher homeostasis model assessment — insu­lin resistance (HOMA-IR) (p = 0.023), free testosterone (p < 0.001), LDL cholesterol levels (p < 0.001) and free androgen index (p < 0.001) compared with the control group. There were significant differences between groups regarding the septal thickness, posterior wall thickness, Left ventricular ejection frac­tion, E/A ratio and left ventricular mass index (for all, p < 0.05). PCOS patients with phenotype 1 and 2 had significantly higher left ventricular mass index than the control group (p < 0.001). In univariate and multivariate analyses, PCOS phenotype, modified Ferriman-Gallwey Score and estradiol were found as variables, which independently could affect the left ventricular mass index. Conclusions: This study showed that women in their twenties who specifically fulfilled criteria for PCOS phenotype-1 according to the Rotterdam criteria, had higher left ventricular mass index and decreased E/A ratio, which might be suggestive of early stage diastolic dysfunction. (Cariol J 2017; 24, 4: 364–373

An experimental study of reduced-voltage operation in modern FPGAs for neural network acceleration

We empirically evaluate an undervolting technique, i.e., underscaling the circuit supply voltage below the nominal level, to improve the power-efficiency of Convolutional Neural Network (CNN) accelerators mapped to Field Programmable Gate Arrays (FPGAs). Undervolting below a safe voltage level can lead to timing faults due to excessive circuit latency increase. We evaluate the reliability-power trade-off for such accelerators. Specifically, we experimentally study the reduced-voltage operation of multiple components of real FPGAs, characterize the corresponding reliability behavior of CNN accelerators, propose techniques to minimize the drawbacks of reduced-voltage operation, and combine undervolting with architectural CNN optimization techniques, i.e., quantization and pruning. We investigate the effect ofenvironmental temperature on the reliability-power trade-off of such accelerators. We perform experiments on three identical samples of modern Xilinx ZCU102 FPGA platforms with five state-of-the-art image classification CNN benchmarks. This approach allows us to study the effects of our undervolting technique for both software and hardware variability. We achieve more than 3X power-efficiency (GOPs/W ) gain via undervolting. 2.6X of this gain is the result of eliminating the voltage guardband region, i.e., the safe voltage region below the nominal level that is set by FPGA vendor to ensure correct functionality in worst-case environmental and circuit conditions. 43% of the power-efficiency gain is due to further undervolting below the guardband, which comes at the cost of accuracy loss in the CNN accelerator. We evaluate an effective frequency underscaling technique that prevents this accuracy loss, and find that it reduces the power-efficiency gain from 43% to 25%.The work done for this paper was partially supported by a HiPEAC Collaboration Grant funded by the H2020 HiPEAC Project under grant agreement No. 779656. The research leading to these results has received funding from the European Union’s Horizon 2020 Programme under the LEGaTO Project (www.legato-project.eu), grant agreement No. 780681.Peer ReviewedPostprint (author's final draft

Triglyceride-glucose index levels in patients with congenital hypogonadotropic hypogonadism and the relationship with endothelial dysfunction and insulin resistance

Introduction: The risk of cardiometabolic diseases is increased in patients with hypogonadism. The triglyceride-glucose (TyG) index is a novel surrogate marker of insulin resistance and is associated with cardiovascular diseases. We investigated the TyG index levels and the relationship with endothelial dysfunction and insulin resistance in patients with congenital hypogonadotropic hypogonadism (CHH). Material and methods: A total of 98 patients with CHH (mean age 21.66 ± 1.99 years) and 98 healthy control subjects (mean age 21.69 ± 1.21 years) were enrolled. The demographic parameters, TyG index, asymmetric dimethylarginine (ADMA), high-sensitivity C-reactive protein (hs-CRP), and homeostatic model assessment of insulin resistance (HOMA-IR) levels were measured for all participants. Results: The patients had higher waist circumference (p < 0.001), triglycerides (p = 0.001), insulin (p = 0.003), HOMA-IR (p = 0.002), ADMA (p < 0.001), and TyG index (p < 0.001) levels and lower HDL-C (p = 0.044) and total testosterone (p < 0.001) levels compared to healthy control subjects. TyG index levels significantly correlated with the ADMA (r = 0.31, p = 0.003) and HOMA-IR (r = 0.32, p < 0.001) levels. TyG index was also determinant of HOMA-IR levels (ß = 0.20, p = 0.018). Conclusion: The results of the present study show that patients with CHH had increased TyG index levels. Also, the TyG index is independently associated with insulin resistance in patients with CHH. Long-term follow-up studies are warranted to find out the role of the TyG index in determining cardiometabolic risk in patients with hypogonadism.

Role of Adipokines and Hormones of Obesity in Childhood Asthma

Purpose: The aim of this study was to evaluate serum levels of leptin, ghrelin, and adiponectin in obese and non-obese children with asthma and in healthy non-asthmatic children, and analyze their relationships with clinical outcomes. Methods: This study enrolled 40 obese and 51 non-obese children with asthma and 20 healthy children. Body mass index and serum leptin, ghrelin, and adiponectin levels were determined in all children. Asthma symptom scores and lung function test results were recorded for subjects with asthma. Results: Serum leptin levels (11.8 +/- 7.9, 5.3 +/- 6.8, and 2.1 +/- 2.4 ng/mL in the obese asthmatic, non-obese asthmatic, and control groups, respectively) and adiponectin levels (12,586.2 +/- 3,724.1; 18,089.3 +/- 6,452.3; and 20,297.5 +/- 3,680.7 ng/mL, respectively) differed significantly among the groups (P<0.001 for all). Mean ghrelin levels were 196.1 +/- 96.8 and 311.9 +/- 352.8 pg/mL in the obese and non-obese asthmatic groups, respectively, and 348.8 +/- 146.4 pg/mL in the control group (P=0.001). The asthma symptom score was significantly higher in the obese children with asthma than in the non-obese children with asthma (P<0.001). Leptin and adiponectin levels were correlated with the asthma symptom score in non-obese children with asthma (r=0.34 and r=-0.62, respectively). Conclusions: Obesity leads to more severe asthma symptoms in children. Moreover, leptin, adiponectin, and ghrelin may play important roles in the inflammatory pathogenesis of asthma and obesity co-morbidity