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Thierry Romeuf - One of the best experts on this subject based on the ideXlab platform.
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On Lack-of-Knowledge theory in structural mechanics
Comptes Rendus Mecanique, 2010Co-Authors: François Louf, Paul Enjalbert, Pierre Ladevèze, Thierry RomeufAbstract:Today, the validation of complex structural models – i.e. the assessment of their quality compared to an experimental reference – remains a major issue. Strictly speaking, the validation problem consists in comparing the response of the numerical model (whether deterministic or stochastic) with complete reality. A first answer to this problem, using Lack-of-Knowledge (LOK) theory, was introduced at LMT-Cachan. This theory is an attempt to “model the unknown” by taking all the sources of uncertainties, including modeling errors, into account through the concept of basic LOKs. In this article, we introduce basic LOKs associated with both the amplitudes and directions of excitations. These basic LOKs are propagated rigorously throughout the mechanical model in order to determine intervals (with stochastic bounds) within which lies a given quantity of interest (stress or displacement). Then, we introduce a strategy for the reduction of Lack of Knowledge, which we illustrate through an academic example.
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On Lack-of-Knowledge theory in structural mechanics
Comptes Rendus Mécanique, 2010Co-Authors: François Louf, Paul Enjalbert, Pierre Ladevèze, Thierry RomeufAbstract:International audienceToday, the validation of complex structural models – i.e. the assessment of their quality compared to an experimental reference – remains a major issue. Strictly speaking, the validation problem consists in comparing the response of the numerical model (whether deterministic or stochastic) with complete reality. A first answer to this problem, using Lack-of-Knowledge (LOK) theory, was introduced at LMT-Cachan. This theory is an attempt to “model the unknown” by taking all the sources of uncertainties, including modeling errors, into account through the concept of basic LOKs. In this article, we introduce basic LOKs associated with both the amplitudes and directions of excitations. These basic LOKs are propagated rigorously throughout the mechanical model in order to determine intervals (with stochastic bounds) within which lies a given quantity of interest (stress or displacement). Then, we introduce a strategy for the reduction of Lack of Knowledge, which we illustrate through an academic example.La validation de modèles structuraux complexes – c'est-à-dire la vérification de leur qualité vis-à-vis d'une référence expérimentale – demeure un verrou scientifique fort. Le véritable problème de validation consiste à comparer la réponse du modèle numérique, qu'il soit déterministe ou pas, avec la réponse de toutes les structures réelles, dans tous les environnements possible. Un premier élément de réponse à ce problème a été introduit via la théorie des méconnaissances au LMT-Cachan. Afin de « modéliser l'inconnu », cette théorie prend en compte toutes les incertitudes, en incluant les erreurs de modèles, à travers le concept de méconnaissances de base. Dans le cet article, on introduit des méconnaissances de base sur les excitations (amplitude et direction). Ces méconnaissances de base sont ensuite propagées à travers le modèle mécanique afin de déterminer des intervalles dont les bornes sont probabilistes, contenant une quantité d'intérêt (contrainte ou déplacement). Ensuite une stratégie de réduction des méconnaissances de base par apport d'information expérimentale est présentée sur un exemple académique
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On the Lack-of-Knowledge (LOK) theory for computational structural elasticity problems
2007Co-Authors: Paul Enjalbert, François Louf, Pierre Ladevèze, Guillaume Puel, Thierry RomeufAbstract:The validation of complex structural models - i.e. the assessment of their quality compared to an experimental reference - remains a major issue today. The true validation problem should be addressed through comparison of the model used classically - whether it is deterministic or not - with the complete reality. A tentative answer through the Lack-of-Knowledge (LOK) theory was introduced in [1
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On a strategy for the reduction of the Lack of Knowledge (LOK) in model validation
Reliability Engineering and System Safety, 2006Co-Authors: Pierre Ladevèze, Guillaume Puel, Thierry RomeufAbstract:Today, the quantification of the quality of a dynamic structural model remains a major issue, and the number of methods being devised in order to validate a model by comparison with an experimental reference keeps increasing. This paper presents a theory based on the concept of Lack of Knowledge, which consists in globalizing the various sources of errors on the substructure level by means of a scalar internal variable, called the LOK variable, defined over an interval whose upper and lower bounds follow probabilistic laws. These intervals, which are defined for each substructure, are then propagated rigorously throughout the mechanical model in order to determine intervals with stochastic bounds within which lies a given quantity of interest defined over the whole structure. Then, a general strategy for the reduction of the Lack of Knowledge is discussed and applied to academic examples as well as industrial cases.
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Lack of Knowledge in structural model validation
Computer Methods in Applied Mechanics and Engineering, 2006Co-Authors: Pierre Ladevèze, Guillaume Puel, Thierry RomeufAbstract:This paper deals with the structural modeling of a family of similar, actual structures taking into account uncertainties and modeling errors. Only errors of the “structural stiffness” type are considered. We develop a new theory in which what we call the Lack of Knowledge (LOK) is defined through an internal variable, whose upper and lower bounds are stochastic, associated with each substructure. Two main questions are discussed: the impact of the basic LOKs on the predicted structural response and the reduction of the basic LOKs through the use of additional information.
Pierre Ladevèze - One of the best experts on this subject based on the ideXlab platform.
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On Lack-of-Knowledge theory in structural mechanics
Comptes Rendus Mecanique, 2010Co-Authors: François Louf, Paul Enjalbert, Pierre Ladevèze, Thierry RomeufAbstract:Today, the validation of complex structural models – i.e. the assessment of their quality compared to an experimental reference – remains a major issue. Strictly speaking, the validation problem consists in comparing the response of the numerical model (whether deterministic or stochastic) with complete reality. A first answer to this problem, using Lack-of-Knowledge (LOK) theory, was introduced at LMT-Cachan. This theory is an attempt to “model the unknown” by taking all the sources of uncertainties, including modeling errors, into account through the concept of basic LOKs. In this article, we introduce basic LOKs associated with both the amplitudes and directions of excitations. These basic LOKs are propagated rigorously throughout the mechanical model in order to determine intervals (with stochastic bounds) within which lies a given quantity of interest (stress or displacement). Then, we introduce a strategy for the reduction of Lack of Knowledge, which we illustrate through an academic example.
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On Lack-of-Knowledge theory in structural mechanics
Comptes Rendus Mécanique, 2010Co-Authors: François Louf, Paul Enjalbert, Pierre Ladevèze, Thierry RomeufAbstract:International audienceToday, the validation of complex structural models – i.e. the assessment of their quality compared to an experimental reference – remains a major issue. Strictly speaking, the validation problem consists in comparing the response of the numerical model (whether deterministic or stochastic) with complete reality. A first answer to this problem, using Lack-of-Knowledge (LOK) theory, was introduced at LMT-Cachan. This theory is an attempt to “model the unknown” by taking all the sources of uncertainties, including modeling errors, into account through the concept of basic LOKs. In this article, we introduce basic LOKs associated with both the amplitudes and directions of excitations. These basic LOKs are propagated rigorously throughout the mechanical model in order to determine intervals (with stochastic bounds) within which lies a given quantity of interest (stress or displacement). Then, we introduce a strategy for the reduction of Lack of Knowledge, which we illustrate through an academic example.La validation de modèles structuraux complexes – c'est-à-dire la vérification de leur qualité vis-à-vis d'une référence expérimentale – demeure un verrou scientifique fort. Le véritable problème de validation consiste à comparer la réponse du modèle numérique, qu'il soit déterministe ou pas, avec la réponse de toutes les structures réelles, dans tous les environnements possible. Un premier élément de réponse à ce problème a été introduit via la théorie des méconnaissances au LMT-Cachan. Afin de « modéliser l'inconnu », cette théorie prend en compte toutes les incertitudes, en incluant les erreurs de modèles, à travers le concept de méconnaissances de base. Dans le cet article, on introduit des méconnaissances de base sur les excitations (amplitude et direction). Ces méconnaissances de base sont ensuite propagées à travers le modèle mécanique afin de déterminer des intervalles dont les bornes sont probabilistes, contenant une quantité d'intérêt (contrainte ou déplacement). Ensuite une stratégie de réduction des méconnaissances de base par apport d'information expérimentale est présentée sur un exemple académique
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On the Lack-of-Knowledge (LOK) theory for computational structural elasticity problems
2007Co-Authors: Paul Enjalbert, François Louf, Pierre Ladevèze, Guillaume Puel, Thierry RomeufAbstract:The validation of complex structural models - i.e. the assessment of their quality compared to an experimental reference - remains a major issue today. The true validation problem should be addressed through comparison of the model used classically - whether it is deterministic or not - with the complete reality. A tentative answer through the Lack-of-Knowledge (LOK) theory was introduced in [1
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On a strategy for the reduction of the Lack of Knowledge (LOK) in model validation
Reliability Engineering and System Safety, 2006Co-Authors: Pierre Ladevèze, Guillaume Puel, Thierry RomeufAbstract:Today, the quantification of the quality of a dynamic structural model remains a major issue, and the number of methods being devised in order to validate a model by comparison with an experimental reference keeps increasing. This paper presents a theory based on the concept of Lack of Knowledge, which consists in globalizing the various sources of errors on the substructure level by means of a scalar internal variable, called the LOK variable, defined over an interval whose upper and lower bounds follow probabilistic laws. These intervals, which are defined for each substructure, are then propagated rigorously throughout the mechanical model in order to determine intervals with stochastic bounds within which lies a given quantity of interest defined over the whole structure. Then, a general strategy for the reduction of the Lack of Knowledge is discussed and applied to academic examples as well as industrial cases.
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Lack of Knowledge in structural model validation
Computer Methods in Applied Mechanics and Engineering, 2006Co-Authors: Pierre Ladevèze, Guillaume Puel, Thierry RomeufAbstract:This paper deals with the structural modeling of a family of similar, actual structures taking into account uncertainties and modeling errors. Only errors of the “structural stiffness” type are considered. We develop a new theory in which what we call the Lack of Knowledge (LOK) is defined through an internal variable, whose upper and lower bounds are stochastic, associated with each substructure. Two main questions are discussed: the impact of the basic LOKs on the predicted structural response and the reduction of the basic LOKs through the use of additional information.
Guillaume Puel - One of the best experts on this subject based on the ideXlab platform.
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On the Lack-of-Knowledge (LOK) theory for computational structural elasticity problems
2007Co-Authors: Paul Enjalbert, François Louf, Pierre Ladevèze, Guillaume Puel, Thierry RomeufAbstract:The validation of complex structural models - i.e. the assessment of their quality compared to an experimental reference - remains a major issue today. The true validation problem should be addressed through comparison of the model used classically - whether it is deterministic or not - with the complete reality. A tentative answer through the Lack-of-Knowledge (LOK) theory was introduced in [1
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On a strategy for the reduction of the Lack of Knowledge (LOK) in model validation
Reliability Engineering and System Safety, 2006Co-Authors: Pierre Ladevèze, Guillaume Puel, Thierry RomeufAbstract:Today, the quantification of the quality of a dynamic structural model remains a major issue, and the number of methods being devised in order to validate a model by comparison with an experimental reference keeps increasing. This paper presents a theory based on the concept of Lack of Knowledge, which consists in globalizing the various sources of errors on the substructure level by means of a scalar internal variable, called the LOK variable, defined over an interval whose upper and lower bounds follow probabilistic laws. These intervals, which are defined for each substructure, are then propagated rigorously throughout the mechanical model in order to determine intervals with stochastic bounds within which lies a given quantity of interest defined over the whole structure. Then, a general strategy for the reduction of the Lack of Knowledge is discussed and applied to academic examples as well as industrial cases.
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Lack of Knowledge in structural model validation
Computer Methods in Applied Mechanics and Engineering, 2006Co-Authors: Pierre Ladevèze, Guillaume Puel, Thierry RomeufAbstract:This paper deals with the structural modeling of a family of similar, actual structures taking into account uncertainties and modeling errors. Only errors of the “structural stiffness” type are considered. We develop a new theory in which what we call the Lack of Knowledge (LOK) is defined through an internal variable, whose upper and lower bounds are stochastic, associated with each substructure. Two main questions are discussed: the impact of the basic LOKs on the predicted structural response and the reduction of the basic LOKs through the use of additional information.
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Extension of the Lack of Knowledge (LOK) theory to force uncertainties
2006Co-Authors: Pierre Ladevèze, Paul Enjalbert, Guillaume Puel, Thierry RomeufAbstract:This paper deals with the structural modeling of a family of similar, actual structures taking into account uncertainties and modeling errors. The concept of Lack of Knowledge (LOK), first introduced in [1,2], consists in globalizing the various sources of errors on the substructure using internal variables, called the LOK variables, defined over an interval whose upper and lower bounds follow probabilistic laws. From these basic LOK, we can derive for the whole structure the effective LOK for a quantity of interest a, resulting in an interval with stochastic bounds that we can compare with experimental values. First, errors on the ”structural stiffness” have been considered [1,2,4]. Here we go further, extending the concept of LOK to modelize errors on applied forces, the mathematical framework being the same.
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Theory of the Lack of Knowledge : basic aspects and applications
2005Co-Authors: Pierre Ladevèze, Paul Enjalbert, Guillaume Puel, Thierry RomeufAbstract:The concept of Lack of Knowledge (LOK) was first introduced in [1, 2]. The basic principle consists in globalizing the various sources of errors on the substructure level using a scalar internal variable, called the LOK variable, defined over an interval whose upper and lower bounds follow probabilistic laws. The question of the impact of the structural model with LOKs on the prediction of the structural response can then be addressed. By a rigorous propagation of the intervals and the probability laws associated to the bounds, the envelope of the possible actual responses is defined, resulting in an interval with stochastic bounds including the structural response of interest. The comparison between these intervals and the experimental values available results in a reduction process of the basic LOKs, which considers the experimental data as additional information. In [3], we presented the first results of this strategy of reduction, starting from an initial overestimated LOK level, given by experience or a priori Knowledge. This paper is focused on the reduction of the LOKs of a actual, industrial structure from the EADS Space Transportation division; this real-case study shows the effectiveness of the strategy of reduction used.
Jenny Kurman - One of the best experts on this subject based on the ideXlab platform.
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Lack of Knowledge of a culture s social axioms and adaptation difficulties among immigrants
Journal of Cross-Cultural Psychology, 2004Co-Authors: Jenny Kurman, Carmel RoneneilonAbstract:Social axioms are the prevailing common and basic beliefs that supposedly guide behavior in a culture. Lack of accurate Knowledge about them may therefore interfere with adaptation to a culture. The present study investigated the implications of in accurate of Knowledge regarding the Israeli social axioms upon how immigrants from Ethiopia and the former Soviet Union have adapted to the Israeli society. Central findings were that a Lack of Knowledge of the social axioms is negatively related to the sociocultural adaptation of immigrants, that Lack of Knowledge regarding social axioms had a unique contribution to prediction of adaptation difficulties over the contribution of Lack of Knowledge about values, and that Knowledge of a culture’s prevailing social axioms contributes more to sociocultural adaptation than does actual proximity of the immigrants’ own social axioms to those of the majority. These findings strongly support the utility of social axioms as cultural descriptors.
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Lack of Knowledge of a Culture’s Social Axioms and Adaptation Difficulties among Immigrants
Journal of Cross-Cultural Psychology, 2004Co-Authors: Jenny Kurman, Carmel Ronen-eilonAbstract:Social axioms are the prevailing common and basic beliefs that supposedly guide behavior in a culture. Lack of accurate Knowledge about them may therefore interfere with adaptation to a culture. The present study investigated the implications of in accurate of Knowledge regarding the Israeli social axioms upon how immigrants from Ethiopia and the former Soviet Union have adapted to the Israeli society. Central findings were that a Lack of Knowledge of the social axioms is negatively related to the sociocultural adaptation of immigrants, that Lack of Knowledge regarding social axioms had a unique contribution to prediction of adaptation difficulties over the contribution of Lack of Knowledge about values, and that Knowledge of a culture’s prevailing social axioms contributes more to sociocultural adaptation than does actual proximity of the immigrants’ own social axioms to those of the majority. These findings strongly support the utility of social axioms as cultural descriptors.
Andrea B Maier - One of the best experts on this subject based on the ideXlab platform.
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Lack of Knowledge contrasts the willingness to counteract sarcopenia among community dwelling adults
Journal of Aging and Health, 2019Co-Authors: Jeanine M Van Ancum, Esmee M Reijnierse, Marijke C Trappenburg, Andrea B Maier, Carel G. M. Meskers, Suey S Y Yeung, Nini H Jonkman, Mirjam PijnappelsAbstract:Objective: Sarcopenia is highly prevalent in older adults. Knowledge among community-dwelling adults is important for effective prevention and treatment of sarcopenia. This study aims to assess current Knowledge about sarcopenia, investigate willingness for treatment and prevention, and awareness of muscle health. Method: Participants who attended health educational events completed a questionnaire on Knowledge about sarcopenia. Self-perceived muscle health was assessed by visual analog scale. Objective muscle measures included muscle mass, handgrip strength, and gait speed. Results: Included participants were 197 (median aged 67.9 years [interquartile range = 57.0-75.1]). Eighteen participants (9%) reported to know what sarcopenia is. Participants' self-perceived muscle health showed a low correlation with all objective muscle measures. 76% were willing, in case of sarcopenia diagnosis, to start treatment and 71% were willing to prevent sarcopenia. Discussion: Knowledge about sarcopenia is limited while participants were willing to start treatment and prevention. Strategies to increase Knowledge among community-dwelling adults are needed.
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Lack of Knowledge and availability of diagnostic equipment could hinder the diagnosis of sarcopenia and its management
PLOS ONE, 2017Co-Authors: Esmee M Reijnierse, Marian A E De Van Der Schueren, Marijke C Trappenburg, Marjan Doves, Carel G. M. Meskers, Andrea B MaierAbstract:Objectives Sarcopenia is an emerging clinical challenge in an ageing population and is associated with serious negative health outcomes. This study aimed to assess the current state of the art regarding the Knowledge about the concept of sarcopenia and practice of the diagnostic strategy and management of sarcopenia in a cohort of Dutch healthcare professionals (physicians, physiotherapists, dietitians and others) attending a lecture cycle on sarcopenia. Material and methods This longitudinal study included Dutch healthcare professionals (n = 223) who were asked to complete a questionnaire before, directly after and five months after (n = 80) attending a lecture cycle on the pathophysiology of sarcopenia, diagnostic strategy and management of sarcopenia, i.e. interventions and collaboration. Results Before attendance, 69.7% of healthcare professionals stated to know the concept of sarcopenia, 21.4% indicated to know how to diagnose sarcopenia and 82.6% had treated patients with suspected sarcopenia. 47.5% used their clinical view as diagnostic strategy. Handgrip strength was the most frequently used objective diagnostic measure (33.9%). Five months after attendance, reported use of diagnostic tests was increased, i.e. handgrip strength up to 67.4%, gait speed up to 72.1% and muscle mass up to 20.9%. Bottlenecks during implementation of the diagnostic strategy were experienced by 67.1%; Lack of awareness among other healthcare professionals, acquisition of equipment and time constraints to perform the diagnostic measures were reported most often. Before attendance, 36.4% stated not to consult a physiotherapists or exercise therapists (PT/ET) or dietitian for sarcopenia interventions, 10.5% consulted a PT/ET, 32.7% a dietitian and 20.5% both a PT/ET and dietitian. Five months after attendance, these percentages were 28.3%, 21.7%, 30.0% and 20.0% respectively. Conclusion The concept of sarcopenia is familiar to most Dutch healthcare professionals but application in practice is hampered, mostly by Lack of Knowledge, availability of equipment, time constraints and Lack of collaboration.
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Lack of Knowledge and diagnostics hinders the implementation of sarcopenia in daily practice
European Geriatric Medicine, 2016Co-Authors: Esmee M Reijnierse, Marijke C Trappenburg, Marjan Doves, Carel G. M. Meskers, M.a.e. De Van Der Schueren, Andrea B MaierAbstract:Objectives: Sarcopenia is an emerging clinical challenge in an ageing population and is associated with negative health outcomes. Healthcare professionals play a key role in diagnosing and managing sarcopenia. This study aimed to assess the current state of Knowledge regarding the definition of sarcopenia, strategy diagnosing it and involved collaborating healthcare professionals among a group of Dutch healthcare professionals attending a lecture cycle on sarcopenia. Methods: The Sarcopenia Road Show comprised lectures and workshops on the pathophysiology of sarcopenia in one session, influencing factors and respective interventions at multiple locations in the Netherlands in 2015. Attending health care professionals were asked to complete a questionnaire (n = 223) before, directly after and after five months. Results: 69.7% of healthcare professionals stated to know the definition of sarcopenia and 82.6% had treated patients with suspected sarcopenia. Only 21.4% indicated to know how to formally diagnose sarcopenia; 47.5% used their clinical view. If diagnostic measures were used, handgrip strength was the most frequent one (33.9%). Five months after attendance, muscle mass was measured by 13.9%, handgrip strength by 50.6% and gait speed by 54.4%. Bottlenecks during the implementation of diagnosing sarcopenia were experienced by 67.1% participants; Lack of Knowledge among collaborating healthcare professionals, the acquisition of equipment and time constrains to perform the diagnostic tests were most often reported. Conclusions: The concept of sarcopenia is familiar to most and diverse healthcare professionals, however Lack of formal Knowledge hinders the implementation of diagnostics and intervention of sarcopenia in daily practice; collaboration should be improved.
