The Experts below are selected from a list of 3693 Experts worldwide ranked by ideXlab platform
Jin Koda - One of the best experts on this subject based on the ideXlab platform.
-
virgo high resolution co survey v circumnuclear Elliptical Ring in ngc 4569
Publications of the Astronomical Society of Japan, 2005Co-Authors: Hiroyuki Nakanishi, Yoshiaki Sofue, Jin KodaAbstract:We present high-resolution (1. �� 8–4. 5) CO data of the Virgo spiral galaxy NGC 4569, obtained using the Nobeyama Millimeter Array. We found that the molecular gas is highly concentrated in the circumnuclear region with two off-center peaks. A CO image with the highest angular resolution of 2. �� 0 ×1. �� 8 shows that six blobs likely form a circumnuclear Elliptical Ring (CER) with a semimajor axis of 720pc. The CER shows a strongly twisted velocity field, and the position–velocity diagram shows significant forbidden velocity components. These kinetic features are understood as being non-circular motion due to a bar-potential. We found that the CER coincides with the Hα bright central core and that the mass ratio of the molecular gas to the dynamical mass is about 18%. These results support a gaseous inflow scenario induced by a weak bar potential and self-gravity of the gas.
-
Virgo High-Resolution CO Survey :V. Circumnuclear Elliptical Ring in NGC 4569
Publications of the Astronomical Society of Japan, 2005Co-Authors: Hiroyuki Nakanishi, Yoshiaki Sofue, Jin KodaAbstract:We present high-resolution ($1\farcs8$ -- $4\farcs5$) CO data of the Virgo spiral galaxy NGC 4569, obtained using the Nobeyama Millimeter Array. We found that the molecular gas is highly concentrated in the circumnuclear region with two off-center peaks. A CO image with the highest angular resolution of $2\farcs0 \times 1\farcs8$ shows that six blobs likely form a circumnuclear Elliptical Ring (CER) with a semi-major axis radius of 720 pc. The CER shows a strongly twisted velocity field, and the position--velocity (PV) diagram shows significant forbidden velocity components. These kinetic features are understood as being non-circular motion due to a bar-potential. We found that the CER coincides with the H$\alpha$ bright central core and that the mass ratio of the molecular gas to the dynamical mass is about 18%. These results support a gaseous inflow scenario induced by a weak bar potential and self-gravity of the gas.
Wei Dong - One of the best experts on this subject based on the ideXlab platform.
-
influence of specimen geometries and drying conditions on concrete cracking in restrained Elliptical Ring tests
Construction and Building Materials, 2019Co-Authors: Wei Dong, Wenyan Yuan, Xiangming Zhou, Xiaoyu ZhaoAbstract:Abstract The restrained shrinkage Elliptical Ring test has been established as an efficient method for assessing the cracking potential of concrete at early ages because an Elliptical Ring can provide a higher degree of restraint compared with a circular one. In this study, a series of circular and Elliptical concrete Rings restrained by steel Rings with various thicknesses were tested under top & bottom surfaces drying or outer circumferential surface drying. By compaRing concrete cracking age under different geometrical and drying conditions, the effects of Ring geometry, restraining steel Ring thickness and drying condition on the cracking process in concrete Rings were revealed. Furthermore, numerical analyses were conducted to investigate the fracture mechanism for circular and Elliptical Rings by applying a fictitious temperature field to simulate the shrinkage effect of concrete. It is found that the increase of steel Ring thickness can enhance the degree of restraint, therefore shorten the cracking age for both circular and Elliptical Rings. However, the improvement is more significant for circular Rings. The fracture processes under the two drying conditions, i.e. top & bottom surfaces drying and outer circumferential surface drying are completely different: for drying from outer circumferential surface, the crack initiates at the outer surface and propagates towards the inner surface; for drying from top & bottom surfaces, the crack initiates partially along the height direction at the inner circumference of a concrete Ring, and propagates along the radial direction, step by step, until the crack propagates throughout the whole Ring wall. In both cases, the self-restraint caused by the non-uniform shrinkage of concrete and the external restraint from the inner steel Ring contribute the driving effects for crack propagation. In general, compared with circular Rings, the Elliptical Rings demonstrate the advantage of providing a higher degree of restraint. The Elliptical Ring test method can, therefore, supplement the traditional circular Ring test method for assessing cracking tendency of concrete with higher cracking resistance.
-
Quantifying the influence of Elliptical Ring geometry on the degree of restraint in a Ring test
Computers & Structures, 2018Co-Authors: Wei Dong, Xiangming Zhou, H. Luo, Gediminas KastiukasAbstract:Abstract A novel Elliptical Ring test method has been proposed to replace the traditional circular Ring test method for the purpose of shortening test duration for assessing cracking tendency of concrete and more conveniently examining crack evolution in concrete Rings. To further explore the mechanism of this new test method, a numerical model was established to analyse stress development and crack initiation in concrete Rings in which a fictitious temperature field simulated the externally applied mechanical effects of concrete shrinkage on concrete causing the same strain as shrinkage does. The proposed numerical model was validated against experimental results and was then used to evaluate the effects of Ring geometry on the degree of restraint to concrete. Moreover, a series of numerical experiments were conducted to derive the expression of the degree of restraint to Elliptical Rings. Through the error analysis of the degree of restraint on concrete properties and Ring geometry, the expression was verified so that it can be used to calculate the degree of restraint provided by the internal steel Ring. According to the derived expression, the restrained Elliptical Ring test can be designed to quantitatively simulate the service condition of concrete in an engineeRing structure more accurately.
-
investigating crack initiation and propagation of concrete in restrained shrinkage circular Elliptical Ring test
Materials and Structures, 2017Co-Authors: Wei Dong, Xiangming ZhouAbstract:The financial support from the National Natural Science Foundation of China under the grants of NSFC 51478083 & 51421064, EngineeRing and Physical Sciences Research Council under the grant of EP/I031952/1, and the National Basic Research Program of China (973 Program, Grant No. 2015CB057703) is gratefully acknowledged.
-
Effects of specimen size on assessment of shrinkage cracking of concrete via Elliptical Rings
Computers & Structures, 2016Co-Authors: Wei Dong, Xiangming Zhou, Gediminas KastiukasAbstract:AbstractAn Elliptical Ring test method is proposed to replace the circular Ring test recommended by ASTM and AASHTO for faster and more reliable assessment of cracking tendency of concrete. Numerical models are also established to simulate stress development and crack initiation/propagation in restrained concrete Rings. Cracking age, position and propagation in various Rings are obtained from numerical analyses that agree well with experimental results. Elliptical thin Rings of certain geometry can shorten the Ring test duration as desirable. In thin Rings, crack initiation is caused by external restraint effect so that a crack occurs at the inner circumference and propagates towards the outer one. In thick Rings, crack initiation is mainly due to the self-restraint effect so that a crack occurs at the outer circumference and propagates towards their inner one. Therefore, thick Elliptical concrete Rings do not necessarily crack earlier than circular ones as observed from experiment
-
assessment of restrained shrinkage cracking of concrete using Elliptical Ring specimens experimental and numerical
Journal of Materials in Civil Engineering, 2014Co-Authors: Xiangming Zhou, Wei Dong, Olayinka OladiranAbstract:A new experimental method is proposed for assessing cracking tendency of concrete using Elliptical Ring specimens subject to restrained shrinkage. To explore the mechanism of this method, a numerical model is developed to analyze stress development and crack initiation in concrete Rings in which the effect of concrete shrinkage is simulated by a fictitious temperature drop applied on concrete causing the same strain as shrinkage does. Stress developed in a concrete Ring is then obtained through a combined thermal and structural analysis. Based on the maximum tensile stress cracking criterion, it is found that numerical results accord well with experimental ones on cracking age for a range of circular and Elliptical concrete Rings with different geometries. Geometrical factor, i.e., the ratio between the major and the minor semi-axes of an Elliptical Ring, is the main factor which affects tensile stress developed and consequently concrete cracking age in restrained Ring specimens. Elliptical Rings with appropriate geometry can enable crack initiating much earlier than circular Rings, which consequently are able to accelerate Ring test for assessing cracking potential of concrete. Finally discussions are made on effects of Ring geometry on features of cracking, crack position and stress development in concrete Rings subject to restrained shrinkage to further explore the mechanism of Elliptical Ring test for assessing cracking potential of concrete.
Eoghan P. Holohan - One of the best experts on this subject based on the ideXlab platform.
-
Unzipping Long Valley: An explanation for vent migration patterns duRing an Elliptical Ring fracture eruption
Geology, 2008Co-Authors: Eoghan P. Holohan, Valentin R. Troll, Benjamin Van Wyk De Vries, John J. Walsh, Thomas R. WalterAbstract:International audienceLong Valley caldera, California, formed duRing the cataclysmic Pleistocene eruption of the Bishop Tuff. Previous stratigraphic and petrologic studies of this eruption deciphered an intriguing pattern of vent migration, thought to mirror the lateral propagation (“unzipping”) of magma-tapping Ring fractures duRing caldera collapse. From scaled analog models, we show that this unzipping pattern was intrinsically related to the high plan-view ellipticity of the precollapse magma chamber roof. We also provide a first-order kinematic explanation for the systematic location of initial Elliptical roof failure and for the lateral propagation of highly Elliptical Ring fractures
-
Unzipping Long Valley: An explanation for vent migration patterns duRing an Elliptical Ring fracture eruption
Geology, 2008Co-Authors: Eoghan P. Holohan, Valentin R. Troll, Benjamin Van Wyk De Vries, John Walsh, Thomas WalterAbstract:Long Valley caldera, California, formed duRing the cataclysmic Pleistocene eruption of the Bishop Tuff. Previous stratigraphic and petrologic studies of this eruption deciphered an intriguing pattern of vent migration, thought to mirror the lateral propagation (“unzipping”) of magma-tapping Ring fractures duRing caldera collapse. From scaled analog models, we show that this unzipping pattern was intrinsically related to the high plan-view ellipticity of the precollapse magma chamber roof. We also provide a first-order kinematic explanation for the systematic location of initial Elliptical roof failure and for the lateral propagation of highly Elliptical Ring fractures.
Xiangming Zhou - One of the best experts on this subject based on the ideXlab platform.
-
influence of specimen geometries and drying conditions on concrete cracking in restrained Elliptical Ring tests
Construction and Building Materials, 2019Co-Authors: Wei Dong, Wenyan Yuan, Xiangming Zhou, Xiaoyu ZhaoAbstract:Abstract The restrained shrinkage Elliptical Ring test has been established as an efficient method for assessing the cracking potential of concrete at early ages because an Elliptical Ring can provide a higher degree of restraint compared with a circular one. In this study, a series of circular and Elliptical concrete Rings restrained by steel Rings with various thicknesses were tested under top & bottom surfaces drying or outer circumferential surface drying. By compaRing concrete cracking age under different geometrical and drying conditions, the effects of Ring geometry, restraining steel Ring thickness and drying condition on the cracking process in concrete Rings were revealed. Furthermore, numerical analyses were conducted to investigate the fracture mechanism for circular and Elliptical Rings by applying a fictitious temperature field to simulate the shrinkage effect of concrete. It is found that the increase of steel Ring thickness can enhance the degree of restraint, therefore shorten the cracking age for both circular and Elliptical Rings. However, the improvement is more significant for circular Rings. The fracture processes under the two drying conditions, i.e. top & bottom surfaces drying and outer circumferential surface drying are completely different: for drying from outer circumferential surface, the crack initiates at the outer surface and propagates towards the inner surface; for drying from top & bottom surfaces, the crack initiates partially along the height direction at the inner circumference of a concrete Ring, and propagates along the radial direction, step by step, until the crack propagates throughout the whole Ring wall. In both cases, the self-restraint caused by the non-uniform shrinkage of concrete and the external restraint from the inner steel Ring contribute the driving effects for crack propagation. In general, compared with circular Rings, the Elliptical Rings demonstrate the advantage of providing a higher degree of restraint. The Elliptical Ring test method can, therefore, supplement the traditional circular Ring test method for assessing cracking tendency of concrete with higher cracking resistance.
-
Quantifying the influence of Elliptical Ring geometry on the degree of restraint in a Ring test
Computers & Structures, 2018Co-Authors: Wei Dong, Xiangming Zhou, H. Luo, Gediminas KastiukasAbstract:Abstract A novel Elliptical Ring test method has been proposed to replace the traditional circular Ring test method for the purpose of shortening test duration for assessing cracking tendency of concrete and more conveniently examining crack evolution in concrete Rings. To further explore the mechanism of this new test method, a numerical model was established to analyse stress development and crack initiation in concrete Rings in which a fictitious temperature field simulated the externally applied mechanical effects of concrete shrinkage on concrete causing the same strain as shrinkage does. The proposed numerical model was validated against experimental results and was then used to evaluate the effects of Ring geometry on the degree of restraint to concrete. Moreover, a series of numerical experiments were conducted to derive the expression of the degree of restraint to Elliptical Rings. Through the error analysis of the degree of restraint on concrete properties and Ring geometry, the expression was verified so that it can be used to calculate the degree of restraint provided by the internal steel Ring. According to the derived expression, the restrained Elliptical Ring test can be designed to quantitatively simulate the service condition of concrete in an engineeRing structure more accurately.
-
investigating crack initiation and propagation of concrete in restrained shrinkage circular Elliptical Ring test
Materials and Structures, 2017Co-Authors: Wei Dong, Xiangming ZhouAbstract:The financial support from the National Natural Science Foundation of China under the grants of NSFC 51478083 & 51421064, EngineeRing and Physical Sciences Research Council under the grant of EP/I031952/1, and the National Basic Research Program of China (973 Program, Grant No. 2015CB057703) is gratefully acknowledged.
-
Effects of specimen size on assessment of shrinkage cracking of concrete via Elliptical Rings
Computers & Structures, 2016Co-Authors: Wei Dong, Xiangming Zhou, Gediminas KastiukasAbstract:AbstractAn Elliptical Ring test method is proposed to replace the circular Ring test recommended by ASTM and AASHTO for faster and more reliable assessment of cracking tendency of concrete. Numerical models are also established to simulate stress development and crack initiation/propagation in restrained concrete Rings. Cracking age, position and propagation in various Rings are obtained from numerical analyses that agree well with experimental results. Elliptical thin Rings of certain geometry can shorten the Ring test duration as desirable. In thin Rings, crack initiation is caused by external restraint effect so that a crack occurs at the inner circumference and propagates towards the outer one. In thick Rings, crack initiation is mainly due to the self-restraint effect so that a crack occurs at the outer circumference and propagates towards their inner one. Therefore, thick Elliptical concrete Rings do not necessarily crack earlier than circular ones as observed from experiment
-
assessment of restrained shrinkage cracking of concrete using Elliptical Ring specimens experimental and numerical
Journal of Materials in Civil Engineering, 2014Co-Authors: Xiangming Zhou, Wei Dong, Olayinka OladiranAbstract:A new experimental method is proposed for assessing cracking tendency of concrete using Elliptical Ring specimens subject to restrained shrinkage. To explore the mechanism of this method, a numerical model is developed to analyze stress development and crack initiation in concrete Rings in which the effect of concrete shrinkage is simulated by a fictitious temperature drop applied on concrete causing the same strain as shrinkage does. Stress developed in a concrete Ring is then obtained through a combined thermal and structural analysis. Based on the maximum tensile stress cracking criterion, it is found that numerical results accord well with experimental ones on cracking age for a range of circular and Elliptical concrete Rings with different geometries. Geometrical factor, i.e., the ratio between the major and the minor semi-axes of an Elliptical Ring, is the main factor which affects tensile stress developed and consequently concrete cracking age in restrained Ring specimens. Elliptical Rings with appropriate geometry can enable crack initiating much earlier than circular Rings, which consequently are able to accelerate Ring test for assessing cracking potential of concrete. Finally discussions are made on effects of Ring geometry on features of cracking, crack position and stress development in concrete Rings subject to restrained shrinkage to further explore the mechanism of Elliptical Ring test for assessing cracking potential of concrete.
Thomas Walter - One of the best experts on this subject based on the ideXlab platform.
-
Unzipping Long Valley: An explanation for vent migration patterns duRing an Elliptical Ring fracture eruption
Geology, 2008Co-Authors: Eoghan P. Holohan, Valentin R. Troll, Benjamin Van Wyk De Vries, John Walsh, Thomas WalterAbstract:Long Valley caldera, California, formed duRing the cataclysmic Pleistocene eruption of the Bishop Tuff. Previous stratigraphic and petrologic studies of this eruption deciphered an intriguing pattern of vent migration, thought to mirror the lateral propagation (“unzipping”) of magma-tapping Ring fractures duRing caldera collapse. From scaled analog models, we show that this unzipping pattern was intrinsically related to the high plan-view ellipticity of the precollapse magma chamber roof. We also provide a first-order kinematic explanation for the systematic location of initial Elliptical roof failure and for the lateral propagation of highly Elliptical Ring fractures.