9 research outputs found

    Metal-Insulator Transitions in Degenerate Hubbard Models and Ax_xC60_{60}

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    Mott-Hubbard metal-insulator transitions in NN-fold degenerate Hubbard models are studied within the Gutzwiller approximation. For any rational filling with xx (integer) electrons per site it is found that metal-insulator transition occurs at a critical correlation energy Uc(N,x)=Uc(N,2N−x)=Îł(N,x)âˆŁÏ”Ë‰(N,x)∣U_c(N,x)=U_c(N,2N-x)=\gamma(N,x)|\bar{\epsilon}(N,x)|, where ϔˉ\bar{\epsilon} is the band energy per particle for the uncorrelated Fermi-liquid state and Îł(N,x)\gamma(N,x) is a geometric factor which increases linearly with xx. We propose that the alkali metal doped fullerides AxC60A_xC_{60} can be described by a 3-fold degenerate Hubbard model. Using the current estimate of band width and correlation energy this implies that most of AxC60{\rm A_xC_{60}}, at integer xx, are Mott-Hubbard insulators and A3C60{\rm A_3C_{60}} is a strongly correlated metal.Comment: 10 pages, Revte

    Ultrasonic quantification of high temperature cyclic damage in an advanced nickel based superalloy

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    Present paper discusses about a new methodology to quantify cyclic damage through ultrasonic measurement. Based on experimental results, correlations have been made between damage accumulated inside the material due to strain excursions and corresponding ultrasonic parameters. It has been proposed that based on the existing correlation between attenuation coefficient and number of cycles to failure, fatigue failure characteristics can be partitioned into two regimes (a) failures due to early nucleation and rapid propagation of cracks and (b) failures due to delayed propagation and crack coalescence. Plastic strain accumulation and surface crack density have been chosen as two physical parameters directly influencing attenuation coefficient and it has been observed that with increasing plastic strain accumulation, ultrasonic attenuation increases. Between two primary echoes of ultrasonic spectra, some secondary defect echoes have been found. A damage descriptor has been introduced by taking difference between the bandwidth of defect echo and badman echo normalized by overall amplitude frequency distributions of backwall echo. It has been found to bear sensitivity towards surface crack density. This quantitative estimation differentiates between the classical descriptions of damage due to dislocation mediated plasticity, micro crack generation and coalescence. (C) 2014 Elsevier B.V. All rights reserved

    Ultrasonic quantiïŹcation of high temperature cyclic damage in an advanced nickel based superalloy

    No full text
    Present paper discusses about a new methodology to quantify cyclic damage through ultrasonic measurement. Based on experimental results, correlations have been made between damage accumulated inside the material due to strain excursions and corresponding ultrasonic parameters. It has been proposed that based on the existing correlation between attenuation coefïŹcient and number of cycles to failure, fatigue failure characteristics can be partitioned into two regimes (a) failures due to early nucleation and rapid propagation of cracks and (b) failures due to delayed propagation and crack coalescence. Plastic strain accumulation and surface crack density have been chosen as two physical parameters directly inïŹ‚uencing attenuation coefïŹcient and it has been observed that with increasing plastic strain accumulation, ultrasonic attenuation increases. Between two primary echoes of ultrasonic spectra, some secondary defect echoes have been found. A damage descriptor has been introduced by taking difference between the bandwidth of defect echo and backwall echo normalized by overall amplitude frequency distributions of backwall echo. It has been found to bear sensitivity towards surface crack density. This quantitative estimation differentiates between the classical descriptions of damage due to dislocation mediated plasticity, micro crack generation and coalescence

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    Not AvailablePotato (Solanum tuberosum ssp. tuberosum) cultivars grown under tropical conditions exhibit comparatively poor yields compared to the temperate conditions, hence, there is need for stable cultivars with greater yields. The interactions of four cultivars with ten environments for 2 years under All India Coordinated Research Project (Potato) across the country for 2 harvesting stage (75 and 90 DAP) revealed that the cultivars were significantly different among themselves for Total Yield (TY) and Marketable Yield (MY) harvested at 75 and 90 DAP at seven and eight environments, respectively. The pooled analysis showed a significant difference for cultivar and environmental main effects for all traits, indicating the existence of cultivars genetic variability justified from the heterogeneity of environments. The significant effect of G×E interaction for TY and MY at 90 DAP, and a non significance for the same traits at 75 DAP clearly indicated that the prevailing environments during early crop stage were uniform as compared to its later harvesting stage. Partitioning of G×E interaction into linear and non linear components were highly significant for all traits, strongly suggesting the real differences in cultivars for regression over environmental means and the response of cultivars to environment was controlled genetically. The cultivar K. Pukhraj was proven as early bulking and stable cultivar for TY and MY at 75 DAP and predictable in nature, as against K. Khyati which was stable cultivar for TY and MY at 90 DAP across growing environments. Hence, K. Khyati, which recorded the highest TY (27.45 t ha-1) and MY (25.24 t ha-1) for harvesting at 75 DAP, and TY (31.28 t ha-1) and MY (28.19 t ha-1) at 90 DAP, can be recommended for tropical conditions.Not Availabl

    Not Available

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    Not AvailablePotato (Solanum tuberosum ssp. tuberosum) cultivars grown under tropical conditions exhibit comparatively poor yields compared to the temperate conditions, hence, there is need for stable cultivars with greater yields. The interactions of four cultivars with ten environments for 2 years under All India Coordinated Research Project (Potato) across the country for 2 harvesting stage (75 and 90 DAP) revealed that the cultivars were significantly different among themselves for Total Yield (TY) and Marketable Yield (MY) harvested at 75 and 90 DAP at seven and eight environments, respectively. The pooled analysis showed a significant difference for cultivar and environmental main effects for all traits, indicating the existence of cultivars genetic variability justified from the heterogeneity of environments. The significant effect of G×E interaction for TY and MY at 90 DAP, and a non significance for the same traits at 75 DAP clearly indicated that the prevailing environments during early crop stage were uniform as compared to its later harvesting stage. Partitioning of G×E interaction into linear and non linear components were highly significant for all traits, strongly suggesting the real differences in cultivars for regression over environmental means and the response of cultivars to environment was controlled genetically. The cultivar K. Pukhraj was proven as early bulking and stable cultivar for TY and MY at 75 DAP and predictable in nature, as against K. Khyati which was stable cultivar for TY and MY at 90 DAP across growing environments. Hence, K. Khyati, which recorded the highest TY (27.45 t ha-1) and MY (25.24 t ha-1) for harvesting at 75 DAP, and TY (31.28 t ha-1) and MY (28.19 t ha-1) at 90 DAP, can be recommended for tropical conditions.ICAR, New Delh
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