The Experts below are selected from a list of 171 Experts worldwide ranked by ideXlab platform
A. Bokota - One of the best experts on this subject based on the ideXlab platform.
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The Numerical Analysis of the Hardening Phenomena of the Hot-work Tool Steel
Procedia Engineering, 2017Co-Authors: Joanna Wróbel, Adam Kulawik, A. BokotaAbstract:Abstract In the paper, to the numerical analysis of quenching phenomena, the complex model of hardening of the hot-work tool steel is used. The numerical algorithm of the thermal phenomena is based on the solving of the heat transfer equation, which takes into account the heat of phase transformations in the solid state, using the finite element method. Model of estimation of phase fractions and their kinetics is based on the continuous cooling diagram (CCT). Phase fractions which occur during the continuous heating and cooling (austenite, pearlite or bainite) are described by Johnson-Mehl-Avrami (JMA) formula. To determine of the formed martensite the modified Koistinen-Marburger (KM) equation is used. The stress and strain are determined by the solution of the equilibrium equations in the rate form using finite element method. The Young's and tangent modulus were dependent on temperature, whereas the yields stress was function of temperature and phase composition of the hardened element. In the model the thermal, Structural, Plastic strains and transformation Plasticity are taken into account. Thermophysical properties occurring in the constitutive relations depended on the temperature and phase composition of the material. To calculate the Plastic strains the Huber-Mises Plasticity condition with isotropic hardening is used. Whereas to determine transformations induced Plasticity the modified Leblond model is applied. Based on the implemented algorithms of the volumetric hardening process (assuming the various temperatures of the cooling medium) the numerical analysis of the phase content, strains and stresses for the hot-work steel (W360) element is performed.
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Analityczno-numeryczna analiza spawania laserowego płaskowników smukłych
Przegląd Spawalnictwa - Welding Technology Review, 2016Co-Authors: Joanna Wróbel, Adam Kulawik, A. BokotaAbstract:W pracy przedstawiono model analityczno-numeryczny oraz analize zjawisk cieplnych, przemian fazowych i zjawisk mechanicznych towarzyszących spawaniu techniką laserową smuklych elementow plaskich. Do rozwiązania zagadnienia przewodzenia ciepla zastosowano metode funkcji Greena. Model szacowania udzialu faz oraz ich kinetyki oparto na wykresie spawalniczym ciąglego chlodzenia (CTPc-S). Udzialy faz metalurgicznych powstających podczas ciąglego nagrzewania i chlodzenia (austenit, perlit lub bainit) wyznaczano rownaniem Johnsona-Mehla i Avramiego. Do wyznaczania tworzącego sie martenzytu wykorzystano zmody kowane rownanie Koistinena i Marburgera. Naprezenia i odksztalcenia wyznaczono z rozwiązania metodą elementow skonczonych rownan rownowagi w formie predkościowej. Uwzgledniono odksztalcenia cieplne, strukturalne, plastyczne oraz odksztalcenia indukowane przemianami fazowymi. Do wyznaczania odksztalcen plastycznych zastosowano warunek plastyczności Hubera-Misesa ze wzmocnieniem izotropowym, natomiast odksztalcenia plastyczne indukowane przemianami fazowymi obliczano formulą Leblonda. Dokonano analizy skladu fazowego i naprezen towarzyszących spawaniu doczolowemu elementow wykonanych z niskoweglowej spawalnej stali (S235). Analize przeprowadzono dla dwoch wersji spawania: pojedynczą wiązką laserową oraz podwojnymi wiązkami, z ktorych jedna zostala uzyta do podgrzewania wstepnego, a druga do spawania. Analytical-numerical analysis of laser welding of thin flat bars Abstract In the paper an analytical-numerical model and the analysis of thermal phenomena, phase transformations and mechanical phenomena occur in laser welding of thin at bars were presented. To solve the heat transfer equation, the method of Green’s function was used. To calculate the phase fractions and their kinetics the model based on the analysis of the continuous cooling diagram for the welding (CCT) is used. Phase fractions which occur during the continuous heating and cooling (austenite, pearlite or bainite) are described by Johnson-Mehl-Avrami (JMA) formula. To determine the formed martensite the modi ed Koistinen-Marburger (KM) equation is used. The stress and strain are determined by the solution of the equilibrium equations in the rate form using nite element method. In the model the thermal, Structural, Plastic strains and induced Plasticity are taken into account. To calculate the Plastic strains the Huber-Mises Plasticity condition with isotropic hardening is used. Whereas to determine transformations induced Plasticity the modi ed Leblond model is applied. The analysis of the phase content and stress state which occur during the butt welding of elements made of low carbon steel (S235) were performed. The calculations were carried out for the two cases of welding: a single laser beam and a double laser beam, where rst was a preheating source and the second the main welding source.
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The Numerical Analysis of the Phenomena of Superficial Hardening of the Hot-Work Tool Steel Elements / Analiza Numeryczna Zjawisk Przypowierzchniowego Hartowania Elementów Ze Stali Narzędziowej Do Pracy Na Gorąco
Archives of Metallurgy and Materials, 2015Co-Authors: A. Bokota, Adam Kulawik, R. Szymczyk, Joanna WróbelAbstract:In the paper the complex model of hardening of the hot-work tool steel is presented. Model of estimation of phase fractions and their kinetics is based on the continuous heating diagram (CHT) and cooling diagram (CCT). Phase fractions which occur during the continuous heating and cooling (austenite, pearlite or bainite) are described by Johnson-Mehl (JM) formula. To determine of the formed martensite the modified Koistinen-Marburger (KM) equation is used. Model takes into account the thermal, Structural, Plastic strains and transformation Plasticity. To calculate the Plastic strains the Huber-Mises Plasticity condition with isotopic hardening is used. Whereas to determine transformations induced Plasticity the Leblond model is applied. The numerical analysis of phase compositions and residual stresses in the hot-work steel (W360) element is considered.
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The numerical model prediction of phase components and stresses distributions in hardened tool steel for cold work
International Journal of Mechanical Sciences, 2015Co-Authors: T. Domański, A. BokotaAbstract:Abstract This study describes modelling of the processes of steel hardening. The first priority was given to a thermal phenomena, phase transformations in solid state and a mechanical phenomena. The issue of heat conductivity was based on the equation of transient heat conductivity with unit source. Numerical algorithms for kinetics of phase transformations and evaluation of fractions of phases were built on the diagrams of continuous heating and cooling of tool steel (CHT and CCT). The theoretical model of phase transformations was then verified by experiments. In modelling of mechanical phenomena, the equilibrium equations and constitutive relations were adopted in the rate form. Plastic strains are determined by the theory of non-isothermal Plastic flow associated with the Huber-Mises condition. The model assumed isotropic and kinematics hardening and besides elastic, thermal, Structural, Plastic strains and transformations Plasticity were included. Thermophysical properties including Young׳s modulus, tangent modulus and yield strength were directly dependent on temperature and material phase composition. The issues of thermo-elastic-Plastic were solved using the finite element method. Implemented algorithms were applied in computer stimulation of hardening of non-alloy tool steel. Numerical analysis of thermal effects and phase transformations, i.e. stresses and strains in mechanical phenomena in a tool steel material undergoing hardening were made.
Wei Qin - One of the best experts on this subject based on the ideXlab platform.
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Length of Acupuncture Training and Structural Plastic Brain Changes in Professional Acupuncturists
PloS one, 2013Co-Authors: Minghao Dong, Ling Zhao, Kai Yuan, Fang Zeng, Jinbo Sun, Karen M. Von Deneen, Fanrong Liang, Jixin Liu, Wei QinAbstract:Background: The research on brain Plasticity has fascinated researchers for decades. Use/training serves as an instrumental factor to influence brain neuroPlasticity. Parallel to acquisition of behavioral expertise, extensive use/training is concomitant with substantial changes of cortical structure. Acupuncturists, serving as a model par excellence to study tactile-motor and emotional regulation Plasticity, receive intensive training in national medical schools following standardized training protocol. Moreover, their behavioral expertise is corroborated during long-term clinical practice. Although our previous study reported functional Plastic brain changes in the acupuncturists, whether or not Structural Plastic changes occurred in acupuncturists is yet elusive.
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Length of Acupuncture Training and Structural Plastic Brain Changes in Professional Acupuncturists
PloS one, 2013Co-Authors: Minghao Dong, Ling Zhao, Kai Yuan, Fang Zeng, Jinbo Sun, Karen M. Von Deneen, Fanrong Liang, Jixin Liu, Wei QinAbstract:The research on brain Plasticity has fascinated researchers for decades. Use/training serves as an instrumental factor to influence brain neuroPlasticity. Parallel to acquisition of behavioral expertise, extensive use/training is concomitant with substantial changes of cortical structure. Acupuncturists, serving as a model par excellence to study tactile-motor and emotional regulation Plasticity, receive intensive training in national medical schools following standardized training protocol. Moreover, their behavioral expertise is corroborated during long-term clinical practice. Although our previous study reported functional Plastic brain changes in the acupuncturists, whether or not Structural Plastic changes occurred in acupuncturists is yet elusive. Cohorts of acupuncturists (N = 22) and non-acupuncturists (N = 22) were recruited. Behavioral tests were delivered to assess the acupuncturists' behavioral expertise. The results confirmed acupuncturists' tactile-motor skills and emotion regulation proficiency compared to non-acupuncturists. Using the voxel-based morphometry technique, we revealed larger grey matter volumes in acupuncturists in the hand representation of the contralateral primary somatosensory cortex (SI), the right lobule V/VI and the bilateral ventral anterior cingulate cortex/ventral medial prefrontal cortex. Grey matter volumes of the SI and Lobule V/VI positively correlated with the duration of acupuncture practice. To our best knowledge, this study provides first evidence for the anatomical alterations in acupuncturists, which would possibly be the neural correlates underlying acupuncturists' exceptional skills. On one hand, we suggest our findings may have ramifications for tactile-motor rehabilitation. On the other hand, our results in emotion regulation domain may serve as a target for our future studies, from which we can understand how modulations of aversive emotions elicited by empathic pain develop in the context of expertise. Future longitudinal study is necessary to establish the presence and direction of a causal link between practice/use and brain anatomy.
Minghao Dong - One of the best experts on this subject based on the ideXlab platform.
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Length of Acupuncture Training and Structural Plastic Brain Changes in Professional Acupuncturists
PloS one, 2013Co-Authors: Minghao Dong, Ling Zhao, Kai Yuan, Fang Zeng, Jinbo Sun, Karen M. Von Deneen, Fanrong Liang, Jixin Liu, Wei QinAbstract:Background: The research on brain Plasticity has fascinated researchers for decades. Use/training serves as an instrumental factor to influence brain neuroPlasticity. Parallel to acquisition of behavioral expertise, extensive use/training is concomitant with substantial changes of cortical structure. Acupuncturists, serving as a model par excellence to study tactile-motor and emotional regulation Plasticity, receive intensive training in national medical schools following standardized training protocol. Moreover, their behavioral expertise is corroborated during long-term clinical practice. Although our previous study reported functional Plastic brain changes in the acupuncturists, whether or not Structural Plastic changes occurred in acupuncturists is yet elusive.
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Length of Acupuncture Training and Structural Plastic Brain Changes in Professional Acupuncturists
PloS one, 2013Co-Authors: Minghao Dong, Ling Zhao, Kai Yuan, Fang Zeng, Jinbo Sun, Karen M. Von Deneen, Fanrong Liang, Jixin Liu, Wei QinAbstract:The research on brain Plasticity has fascinated researchers for decades. Use/training serves as an instrumental factor to influence brain neuroPlasticity. Parallel to acquisition of behavioral expertise, extensive use/training is concomitant with substantial changes of cortical structure. Acupuncturists, serving as a model par excellence to study tactile-motor and emotional regulation Plasticity, receive intensive training in national medical schools following standardized training protocol. Moreover, their behavioral expertise is corroborated during long-term clinical practice. Although our previous study reported functional Plastic brain changes in the acupuncturists, whether or not Structural Plastic changes occurred in acupuncturists is yet elusive. Cohorts of acupuncturists (N = 22) and non-acupuncturists (N = 22) were recruited. Behavioral tests were delivered to assess the acupuncturists' behavioral expertise. The results confirmed acupuncturists' tactile-motor skills and emotion regulation proficiency compared to non-acupuncturists. Using the voxel-based morphometry technique, we revealed larger grey matter volumes in acupuncturists in the hand representation of the contralateral primary somatosensory cortex (SI), the right lobule V/VI and the bilateral ventral anterior cingulate cortex/ventral medial prefrontal cortex. Grey matter volumes of the SI and Lobule V/VI positively correlated with the duration of acupuncture practice. To our best knowledge, this study provides first evidence for the anatomical alterations in acupuncturists, which would possibly be the neural correlates underlying acupuncturists' exceptional skills. On one hand, we suggest our findings may have ramifications for tactile-motor rehabilitation. On the other hand, our results in emotion regulation domain may serve as a target for our future studies, from which we can understand how modulations of aversive emotions elicited by empathic pain develop in the context of expertise. Future longitudinal study is necessary to establish the presence and direction of a causal link between practice/use and brain anatomy.
Brahim Tighilet - One of the best experts on this subject based on the ideXlab platform.
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neurogenic potential of the vestibular nuclei and behavioural recovery time course in the adult cat are governed by the nature of the vestibular damage
PLOS ONE, 2011Co-Authors: Sophie Dutheil, Michel Lacour, Brahim TighiletAbstract:Functional and reactive neurogenesis and astrogenesis are observed in deafferented vestibular nuclei after unilateral vestibular nerve section in adult cats. The newborn cells survive up to one month and contribute actively to the successful recovery of posturo-locomotor functions. This study investigates whether the nature of vestibular deafferentation has an incidence on the neurogenic potential of the vestibular nuclei, and on the time course of behavioural recovery. Three animal models that mimic different vestibular pathologies were used: unilateral and permanent suppression of vestibular input by unilateral vestibular neurectomy (UVN), or by unilateral labyrinthectomy (UL, the mechanical destruction of peripheral vestibular receptors), or unilateral and reversible blockade of vestibular nerve input using tetrodotoxin (TTX). Neurogenesis and astrogenesis were revealed in the vestibular nuclei using bromodeoxyuridine (BrdU) as a newborn cell marker, while glial fibrillary acidic protein (GFAP) and glutamate decarboxylase 67 (GAD67) were used to identify astrocytes and GABAergic neurons, respectively. Spontaneous nystagmus and posturo-locomotor tests (static and dynamic balance performance) were carried out to quantify the behavioural recovery process. Results showed that the nature of vestibular loss determined the cellular Plastic events occurring in the vestibular nuclei and affected the time course of behavioural recovery. Interestingly, the deafferented vestibular nuclei express neurogenic potential after acute and total vestibular loss only (UVN), while non-Structural Plastic processes are involved when the vestibular deafferentation is less drastic (UL, TTX). This is the first experimental evidence that the vestibular complex in the brainstem can become neurogenic under specific injury. These new data are of interest for understanding the factors favouring the expression of functional neurogenesis in adult mammals in a brain repair perspective, and are of clinical relevance in vestibular pathology.
Antonio Aguado - One of the best experts on this subject based on the ideXlab platform.
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Plastic fibres as the only reinforcement for flat suspended slabs: Experimental investigation and numerical simulation
Construction and Building Materials, 2014Co-Authors: Pablo Pujadas, Ana Blanco, Sergio Henrique Pialarissi Cavalaro, Antonio AguadoAbstract:Abstract This paper focuses on the study of the Structural response of hyperstatic concrete flat suspended slabs reinforced only with Structural Plastic macro-fibres. First, the experimental program is described and then the results obtained are presented. The slabs tested maintained a high load level after cracking showing a ductile behaviour with great stress redistribution capacity. Next, the tests were simulated by means of a finite element software with constitutive models according to the specifications of RILEM and the Spanish Structural Concrete Code (EHE). The numerical results in terms of load/mid-span deflection were compared with the experimental results. The predictions provided by the codes and guideline models clearly overestimated the experimental results, which suggests the need to review the constitutive models used for Plastic fibre-reinforced concrete.
