The Experts below are selected from a list of 324 Experts worldwide ranked by ideXlab platform
Guojun Zhang - One of the best experts on this subject based on the ideXlab platform.
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String-theoretic deformation of the Parke-Taylor Factor
Physical Review D, 2017Co-Authors: Sebastian Mizera, Guojun ZhangAbstract:Scattering amplitudes in a range of quantum field theories can be computed using the Cachazo-He-Yuan (CHY) formalism. In theories with colour ordering, the key ingredient is the so-called Parke-Taylor Factor. In this note we give a fully $\text{SL}(2,\mathbb{C})$-covariant definition and study the properties of a new integrand called the string Parke-Taylor Factor. It has an $\alpha'$ expansion whose leading coefficient is the field-theoretic Parke-Taylor Factor. Its main application is that it leads to a CHY formulation of open string tree-level amplitudes. In fact, the definition of the string Parke-Taylor Factor was motivated by trying to extend the compact formula for the first $\alpha'$ correction found by He and Zhang, while the main ingredient in its definition is a determinant of a matrix introduced in the context of string theory by Stieberger and Taylor.
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a string deformation of the parke Taylor Factor
Physical Review D, 2017Co-Authors: Sebastian Mizera, Guojun ZhangAbstract:Scattering amplitudes in a range of quantum field theories can be computed using the Cachazo-He-Yuan (CHY) formalism. In theories with colour ordering, the key ingredient is the so-called Parke-Taylor Factor. In this note we give a fully $\text{SL}(2,\mathbb{C})$-covariant definition and study the properties of a new integrand called the string Parke-Taylor Factor. It has an $\alpha'$ expansion whose leading coefficient is the field-theoretic Parke-Taylor Factor. Its main application is that it leads to a CHY formulation of open string tree-level amplitudes. In fact, the definition of the string Parke-Taylor Factor was motivated by trying to extend the compact formula for the first $\alpha'$ correction found by He and Zhang, while the main ingredient in its definition is a determinant of a matrix introduced in the context of string theory by Stieberger and Taylor.
Henryk Paul - One of the best experts on this subject based on the ideXlab platform.
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Microstructure and microtexture evolution during strain path changes of an initially stable Cu single crystal
Acta Materialia, 2010Co-Authors: Henryk Paul, Claire Maurice, J. DriverAbstract:The microstructure and microtexture evolution in a deformed Goss oriented crystal were characterized after a sample rotation and consequent change in strain path, over a range of scales by optical microscopy, high resolution scanning electron microscopy equipped with field emission gun and electron packscattered diffraction facilities and transmission electron microscopy orientation mapping. High purity copper single crystals with initial Goss{1 1 0}〈0 0 1〉 orientation were channel-die compressed 59% to develop a homogeneous structure composed of two sets of symmetrical primary microbands. New samples with ND rotated orientations of Goss{1 1 0}〈0 0 1〉, brass{1 1 0}〈1 1 2〉, M{1 1 0}〈1 1 1〉 and H{1 1 0}〈0 0 1〉, were then cut out and further compressed in channel-die by a few per cent. The change in flow stress could be correlated with the change in dislocation substructure and microtexture, particularly along shear bands initiated by the strain path change. In the H{1 1 0}〈0 1 1〉 and M{1 1 0}〈1 1 1〉 orientations, the flow stress increased by Taylor Factor hardening then decreased by intense macroscopic shear band (MSB) formation. In the softer brass orientation and in the absence of Taylor Factor hardening, more diffuse MSB formation occurred. The local rotations in the band were used to deduce the possible local slip systems initiated during the strain path change.
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Microstructure and microtexture evolution during strain path changes of an initially stable Cu single crystal
Acta Materialia, 2010Co-Authors: Henryk Paul, Claire Maurice, Julian H. DriverAbstract:International audienceThe microstructure and microtexture evolution in a deformed Goss oriented crystal were characterized after a sample rotation and consequent change in strain path, over a range of scales by optical microscopy, high resolution scanning electron microscopy equipped with field emission gun and electron packscattered diffraction facilities and transmission electron microscopy orientation mapping. High purity copper single crystals with initial Goss{1 1 0}〈0 0 1〉 orientation were channel-die compressed 59% to develop a homogeneous structure composed of two sets of symmetrical primary microbands. New samples with ND rotated orientations of Goss{1 1 0}〈0 0 1〉, brass{1 1 0}〈1 1 2〉, M{1 1 0}〈1 1 1〉 and H{1 1 0}〈0 0 1〉, were then cut out and further compressed in channel-die by a few per cent. The change in flow stress could be correlated with the change in dislocation substructure and microtexture, particularly along shear bands initiated by the strain path change. In the H{1 1 0}〈0 1 1〉 and M{1 1 0}〈1 1 1〉 orientations, the flow stress increased by Taylor Factor hardening then decreased by intense macroscopic shear band (MSB) formation. In the softer brass orientation and in the absence of Taylor Factor hardening, more diffuse MSB formation occurred. The local rotations in the band were used to deduce the possible local slip systems initiated during the strain path change
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Large strain deformation substructures and local crystallography in {100}/{110} aluminium bicrystals
Archives of Metallurgy and Materials, 2006Co-Authors: Henryk Paul, Claire Maurice, Julian Driver, Marcin BijakAbstract:Symmetrically oriented bicrystals of pure Al(99.998%) have been deformed in channel-die compression up to strains of similar to 1.5 to correlate the dislocation substructures and the slip system distributions. The study has focused on structure development in (100)< 001 >/{110}< 001 > (cube/Goss)-oriented bicrystals with the grain boundary situated parallel to the compression plane. Both orientations have the same nominal Taylor Factor and deform macroscopically by the same amount but have stable (Goss) and unstable (cube) micro-deformation behavior. The character of the deformation substructure was determined by systematic local orientation measurements using high resolution EBSD in a SEM-FEG scanning electron microscope and also by transmission electron microscopy (TEM) and the CBED technique at specific locations. The bicrystal deformation analysis shows that the microtexture evolution within neighboring grains is quite different. Very strong deformation banding is observed within crystallites with the unstable orientation, i.e. cube-oriented grain forms classical deformation bands of slightly and strongly dislocated areas. The Goss-oriented grains within bicrystals are more stable under plane strain conditions and do not show any tendency to strain inhomogeneties except for the zone near the grain boundary.
Indradev Samajdar - One of the best experts on this subject based on the ideXlab platform.
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On the widths of orientation gradient zones adjacent to grain boundaries
Scripta Materialia, 2009Co-Authors: Sushil Mishra, Prita Pant, K. L. Narasimhan, Anthony D. Rollett, Indradev SamajdarAbstract:Recrystallized commercial purity aluminum samples were deformed to true strains of 0.095 and 0.262 by uniaxial tension. Microtexture data were analyzed to quantify orientation gradients between the grain interior and the grain boundary of nearest neighbor crystallites. The gradients were characterized in terms of the length over which a significant gradient was observed and the maximum misorientation. Estimated length ratios were observed to obey an inverse power law relationship with Taylor Factor(s). (C) 2009 Acta Materialia Inc
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Deformation twinning in AISI 316L austenitic stainless steel: role of strain and strain path
Materials Science and Technology, 2007Co-Authors: Sushil Mishra, K. L. Narasimhan, Indradev SamajdarAbstract:AISI 316L austenitic stainless steel was deformed at different strain and strain paths. The twin boundaries in the deformed microstructure had two possible origins: decay of original annealing twins and generation of deformation twins. Assuming that rotations of grains, specifically grains on both sides of a twin boundary, are responsible for the twin decay, a simple model was proposed to bring out the domain of relative twin generation. A biaxial strain path, in general, was associated with strong twin generation - an association or dependency linked to the texture estimated values of Taylor Factor. Formation of strain induced martensite was also observed to be strain and strain path dependent and was more in biaxial strain path
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Development of Cold Rolled Texture and Microstructure in a Hot Band Fe-3%Si Steel
ISIJ International, 2002Co-Authors: S. Cicale, Indradev Samajdar, Bert Verlinden, G. Abbruzzese, P. Van HoutteAbstract:Hot band Fe-3%Si steel (CRGO or cold rolled grain oriented) was cold rolled with different reductions. The main objective of this study was an overall understanding of deformation texture and microstructure development. Hot band CRGO had a strong α-fiber (RD// ) texture. Cold reduction strengthened the a and y (ND// ) fibers, but weakened θ (ND// ). All Taylor type deformation texture models were reasonably successful in predicting these bulk texture developments, and the Lamel model seems to be the 'best-fit' model, both in terms of a 'deviation' parameter (indicating differences between experimental and simulated values of idealized texture components) and a 'trend' parameter (indicating the relative change(s) in texture components with strain). The striking feature of the microstructure was the 'selective' appearance of grain interior strain localization's. These appeared at approximately 37° with the rolling direction (RD). Though 37° bands appeared only in orientations with high Taylor Factor (M), the absolute value of the Taylor Factor alone, was not enough for the appearance of such bands. Negative textural softening or (dM/de) values, on the other hand, were always associated with the appearance of 37° bands, justifying or explaining their formation on the basis of a macroscopic plastic instability theory.
Terence G. Langdon - One of the best experts on this subject based on the ideXlab platform.
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Effect of annealing on wear resistance and electroconductivity of copper processed by high-pressure torsion
Journal of Materials Science, 2013Co-Authors: Alexander P. Zhilyaev, Iaroslava Shakhova, Andrey Belyakov, Rustam Kaibyshev, Terence G. LangdonAbstract:The influences of annealing temperature on the wear properties and electrical conductivity of Cu were studied after processing by high-pressure torsion (HPT). The annealing of Cu specimens processed by HPT leads to an increase in electroconductivity and a decrease in the wear rate. It is apparent that a nanotribolayer at the surface induced during wear sliding plays a more significant role than the ultrafine-grained structure. A slight increase was observed in the microhardness of HPT copper specimens upon annealing at a relatively low temperature (100 °C), and this is most likely due to a change in texture. The annealing leads to an increase in the Taylor Factor by ~5 %, which is in good agreement with the increase in the microhardness level which is also by ~5 %. It is apparent that low-temperature annealing of HPT copper may produce optimal properties of the specimens including high strength and electroconductivity with a lower wear rate.
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Evolution of microhardness and microstructure in a cast Al–7 % Si alloy during high-pressure torsion
Journal of Materials Science, 2012Co-Authors: Tarang Mungole, Naresh Nadammal, Kunal Dawra, Praveen Kumar, Megumi Kawasaki, Terence G. LangdonAbstract:Disks of a cast Al-7 % Si alloy were processed through high-pressure torsion (HPT) for 1/4, 1/2, 1, 5, and 10 revolutions under a pressure of 6.0 GPa and at temperatures of 298 and 445 K. The hardness of the samples after processing was significantly higher than in the cast sample, and the hardness profiles across the samples became more uniform with increasing numbers of turns. Processing at higher temperature gave lower hardness values. Experiments were conducted to examine the effects of HPT processing on various microstructural aspects of the cast Al-7 % Si alloy such as the grain size, the Taylor Factor, and the fraction of high-angle grain boundaries. The results demonstrate that there is a correlation between trends in the microhardness values and the observed microstructures
Sebastian Mizera - One of the best experts on this subject based on the ideXlab platform.
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String-theoretic deformation of the Parke-Taylor Factor
Physical Review D, 2017Co-Authors: Sebastian Mizera, Guojun ZhangAbstract:Scattering amplitudes in a range of quantum field theories can be computed using the Cachazo-He-Yuan (CHY) formalism. In theories with colour ordering, the key ingredient is the so-called Parke-Taylor Factor. In this note we give a fully $\text{SL}(2,\mathbb{C})$-covariant definition and study the properties of a new integrand called the string Parke-Taylor Factor. It has an $\alpha'$ expansion whose leading coefficient is the field-theoretic Parke-Taylor Factor. Its main application is that it leads to a CHY formulation of open string tree-level amplitudes. In fact, the definition of the string Parke-Taylor Factor was motivated by trying to extend the compact formula for the first $\alpha'$ correction found by He and Zhang, while the main ingredient in its definition is a determinant of a matrix introduced in the context of string theory by Stieberger and Taylor.
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a string deformation of the parke Taylor Factor
Physical Review D, 2017Co-Authors: Sebastian Mizera, Guojun ZhangAbstract:Scattering amplitudes in a range of quantum field theories can be computed using the Cachazo-He-Yuan (CHY) formalism. In theories with colour ordering, the key ingredient is the so-called Parke-Taylor Factor. In this note we give a fully $\text{SL}(2,\mathbb{C})$-covariant definition and study the properties of a new integrand called the string Parke-Taylor Factor. It has an $\alpha'$ expansion whose leading coefficient is the field-theoretic Parke-Taylor Factor. Its main application is that it leads to a CHY formulation of open string tree-level amplitudes. In fact, the definition of the string Parke-Taylor Factor was motivated by trying to extend the compact formula for the first $\alpha'$ correction found by He and Zhang, while the main ingredient in its definition is a determinant of a matrix introduced in the context of string theory by Stieberger and Taylor.
