19 research outputs found
Toepassing en verandering van de ROQ methode. Kwantificering en optimalisatie van logistieke dienstverlening.
No full textTechnology, Policy and Managemen
Probability of Delamination Detection for CFRP DCB Specimens Using Rayleigh Distributed Optical Fiber Sensors
No full textDistributed Optical Fiber Sensors (DOFS) show several inherent benefits with respect to conventional strain-sensing technologies and represent a key technology for Structural Health Monitoring (SHM). Despite the solid motivation behind DOFS-based SHM systems, their implementation for real-time structural assessment is still unsatisfactory outside academia. One of the main reasons is the lack of rigorous methodologies for uncertainty quantification, which hinders the performance assessment of the monitoring system. The concept of Probability of Detection (POD) should function as the guiding light in this process, but precautions must be taken to apply this concept to SHM, as it has been originally developed for Non-Destructive Evaluation techniques. Although DOFS have been the object of numerous studies, a well-established methodology for their performance evaluation in terms of PODs is still missing. In the present work, the concept of Probability of Delamination Detection (POD2) is proposed for a DOFS network; Carbon Fiber-Reinforced Polymers (CFRP) Double-Cantilever Beam (DCB) specimens equipped with DOFS have been tested under static loading, and the strain patterns along with the relative observed delamination size have been collected to generate an adequate database for the POD analysis, suggesting a reference methodology to quantify the performance of DOFS for delamination detection.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Structural Integrity & Composite
Strain-based delamination prediction in fatigue loaded CFRP coupon specimens by deep learning and static loading data
No full textMachine learning (ML) methods for the structural health monitoring (SHM) of composite structures rely on sufficient domain knowledge as they typically demand to extract damage-sensitive features from raw data before training the ML model. In practice, prior knowledge is not available in most cases. Deep learning (DL) methods, on the other hand, can obtain higher-level features from raw input data and have proven superior in several applications. This paper proposes a Convolutional Neural Network (CNN) based approach for the delamination prediction in CFRP double cantilever beam (DCB) specimens using raw local array strain measurements via distributed optical fiber sensors. The conventional CNN architecture is modified to perform regression, as the delamination size is a continuous value. 1D and 2D CNN architectures are deployed and compared and different techniques are exploited to encode 1D spatial strain pattern series as 2D images. Raw strain patterns collected during static testing are used to train the CNNs, while testing is performed on unseen raw fatigue strain patterns, showing the CNN ability to automatically extract discriminative features from the non-pre-processed static strain pattern-based signals that generalize to raw fatigue signals as well. This strategy has the potential to reduce fatigue testing expenditures while also shortening the time required to gather training data.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Structural Integrity & Composite
PCB pollution continues to impact populations of orcas and other dolphins in European waters
No full textNHM Repositor
Qualification of distributed optical fiber sensors using probability of detection curves for delamination in composite laminates
No full textDespite the promising application of Distributed Optical Fiber Sensors (DOFS) in monitoring damage in composite structures, their implementation outside academia is still unsatisfactory due to the lack of a systematic approach to assessing their damage detection performance. The existing tool developed for non-destructive evaluation, Probability of Detection (POD) curves, needs to be adapted for structural health monitoring applications to account for spatial and temporal dependency. Damage detection performance with DOFS is deeply related to the inherent variability sources of the system, the strain transfer properties of the optical fiber, and the loading conditions, which determine the damage-induced strain on the structure. This paper establishes a systematic approach based on the Length at Detection (LaD) method to qualify DOFS for damage detection in composites under different scenarios. Specifically, this study considers two DOFS with different strain transfer properties for monitoring delamination in carbon fiber reinforced polymers double-cantilever beam specimens under mode I quasi-static and fatigue loading. The POD curves derived from the LaD method confirm that this methodology can quantify the change in the detection performance due to the DOFS type and the loading conditions. The study also proposes a practical solution to compare POD curves obtained with different sample sizes, by introducing the concept of virtual specimens to simulate the lower confidence bound convergence.</p
Technological activities and their impact on the financial performance of the firm: exploitation and exploration within and between firms
No full textThis article analyzes the consequences for financial performance of technology strategies categorized along two dimensions: (1) explorative versus exploitative and (2) solitary versus collaborative. The financial performance implications of firms’ positioning along these two dimensions has important managerial implications, but has received only limited attention in prior studies. Drawing on organizational learning theory and technology alliances literature, a set of hypotheses on the performance implications of firms’ technology strategies are derived. These hypotheses are tested empirically on a panel dataset (1996-2003) of 168 R&D-intensive firms based in Japan, the US and Europe and situated in five different industries (chemicals, pharmaceuticals, ICT, electronics, non-electrical machinery). Patent data are used to construct indicators of explorative versus exploitative technological activities (activities in new or existing technology domains) and collaborative versus solitary technological activities (joint versus single patent ownership). The financial performance of firms is measured via a market value indicator: Tobin’s Q index.
The analyses confirm the existence of an inverted U-shape relationship between the share of explorative technological activities and financial performance. In addition, it is observed that most sample firms do not reach the optimal level of explorative technological activities. These findings point to the relevance of creating a balance between exploitation and exploration in the context of technological activities. Moreover, they suggest that, for the majority of R&D intensive firms, reaching such a balance between exploration and exploitation implies investing additional efforts and resources in exploring new knowledge domains. The analyses also show that firms, engaging more intensively in collaboration, perform relatively stronger in explorative activities. At the same time, a negative relationship between the share of collaborative technological activities and a firm’s market value is observed. Contrary to our expectations, it is collaboration in explorative technological activities, rather than collaboration in exploitative technological activities, that leads to a reduction in firm value. These findings question the relevance of open business models for technological activities. In particular, they suggest that the potential advantages of collaboration for (explorative) technological activities (i.e. access to complementary knowledge from other partners, sharing of technological costs and risks) might not compensate for the potential disadvantages, such as the incurred increase in coordination costs and the need to share innovation rewards across innovation partners.sponsorship: Author names appear alphabetically. The authors want to thank FWO Flanders (project: G.0468.09) for financial support to conduct this research. (FWO Flanders|G.0468.09)status: Publishe
Hepatocyte Growth Factor and Retinal Arteriolar Diameter in Singapore Chinese
No full textObjective: To assess if natural genetic variation in hepatocyte growth factor (HGF) is associated with altered retinal vessel diameter. Design: Two-stage cohort study. Participants and Controls: Discovery set (set 1, n = 682 children) and confirmatory set (set 2, n = 1293 adults). Methods: Children in the discovery set were genotyped for a panel of genetic markers within HGF. Markers that were found to be associated significantly with altered retinal vessel diameter then were genotyped in the confirmatory set. Main Outcome Measures: Increased or decreased retinal vessel diameter. Results: In the discovery set (n = 682 Chinese children aged 7 to 12 years), the variant allele of 4 HGF single nucleotide polymorphisms (SNPs) demonstrated association with larger retinal arteriolar diameter. The effect of the variant allele seems to be strongest within a recessive model of inheritance (Pmin = 4.6×10-3) for all 4 SNPs. When these 4 SNPs were assessed in a confirmatory study comprising 1293 Chinese adults, successful replication was observed for one of them (HGF +63962; rs5745752); the variant allele was observed to correlate with significantly larger retinal arteriolar diameter, with its effect again strongest within a model of recessive inheritance (P = 0.049). Analyzed as a quantitative trait, recessive carriage at HGF +63962 resulted in on average a 3.5-μm increase in retinal arteriolar diameter among children and a 2.5-μm increase in adults (P = 7.0×10-3, analysis of variance; P = 3.0×10-3, Kruskal-Wallis test). Conclusions: This study suggests that natural variation within HGF is involved in the control of retinal arteriolar diameter and may be important in the pathogenesis of microvascular disease in individuals of Chinese descent. Financial Disclosure(s): The author(s) have no proprietary or commercial interest in any materials discussed in this article. © 2010 American Academy of Ophthalmology.link_to_subscribed_fulltex
Promotion of exclusive breast-feeding at scale within routine health services: impact of breast-feeding counselling training for community health workers in Recife, Brazil.
No full textOBJECTIVE: Breast-feeding counselling has been identified as the intervention with the greatest potential for reducing child deaths, but there is little experience in delivering breast-feeding counselling at scale within routine health systems. The study aim was to compare rates of exclusive breast-feeding associated with a breast-feeding counselling intervention in which community health agents (CHA) received 20 h of training directed at counselling and practical skills with rates pre-intervention when CHA received 4 h of didactic teaching. DESIGN: Cross-sectional surveys of breast-feeding practices were conducted pre- and post-intervention in random samples of 1266 and 1245 infants aged 0-5.9 months, respectively. SETTING: Recife, Brazil, with a population of 2 million. SUBJECTS: CHA (n 1449) of Brazil's Family Health Programme were trained to provide breast-feeding counselling at home visits. RESULTS: Rates of exclusive breast-feeding improved when CHA were trained to provide breast-feeding counselling and were significantly higher by 10-13 percentage points at age 3-5.9 months when compared with pre-intervention rates (P < 0.05). Post-intervention point prevalence of exclusive breast-feeding for infants aged <4 months was 63% and for those aged <6 months was 50%. CONCLUSIONS: Multifunctional CHA were able to deliver breast-feeding counselling at scale within a routine health service and this was associated with a significant increase in rates of exclusive breast-feeding. The study reinforces the need to focus training on counselling and practical skills; a key component was an interactive style that utilized the knowledge and experience of CHA. The findings are relevant to the call by international organizations to scale up breast-feeding counselling
