The Experts below are selected from a list of 138 Experts worldwide ranked by ideXlab platform
Masao Saito - One of the best experts on this subject based on the ideXlab platform.
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The Brightness Temperature of the Quiet Solar Chromosphere at 2.6 mm
Solar Physics, 2017Co-Authors: Kazumasa Iwai, Masumi Shimojo, Shinichiro Asayama, Tetsuhiro Minamidani, Stephen White, Timothy Bastian, Masao SaitoAbstract:The Absolute brightness Temperature of the Sun at millimeter wavelengths is an important diagnostic of the solar chromosphere. Because the Sun is so bright, measurement of this property usually involves the operation of telescopes under extreme conditions and requires a rigorous performance assessment of the telescope. In this study, we establish solar observation and calibration techniques at 2.6 mm wavelength for the Nobeyama 45 m telescope and accurately derive the Absolute solar brightness Temperature. We tune the superconductor–insulator–superconductor (SIS) receiver by inducing different bias voltages onto the SIS mixer to prevent saturation. Then, we examine the linearity of the receiver system by comparing outputs derived from different tuning conditions. Furthermore, we measure the lunar filled beam efficiency of the telescope using the New Moon, and then derive the Absolute brightness Temperature of the Sun. The derived solar brightness Temperature is 7700 ± 310 K $7700 \pm 310~\mbox{K}$ at 115 GHz. The telescope beam pattern is modeled as a summation of three Gaussian functions and derived using the solar limb. The real shape of the Sun is determined via deconvolution of the beam pattern from the observed map. Such well-calibrated single-dish observations are important for high-resolution chromospheric studies because they provide the Absolute Temperature Scale that is lacking from interferometer observations.
Kazumasa Iwai - One of the best experts on this subject based on the ideXlab platform.
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The Brightness Temperature of the Quiet Solar Chromosphere at 2.6 mm
Solar Physics, 2017Co-Authors: Kazumasa Iwai, Masumi Shimojo, Shinichiro Asayama, Tetsuhiro Minamidani, Stephen White, Timothy Bastian, Masao SaitoAbstract:The Absolute brightness Temperature of the Sun at millimeter wavelengths is an important diagnostic of the solar chromosphere. Because the Sun is so bright, measurement of this property usually involves the operation of telescopes under extreme conditions and requires a rigorous performance assessment of the telescope. In this study, we establish solar observation and calibration techniques at 2.6 mm wavelength for the Nobeyama 45 m telescope and accurately derive the Absolute solar brightness Temperature. We tune the superconductor–insulator–superconductor (SIS) receiver by inducing different bias voltages onto the SIS mixer to prevent saturation. Then, we examine the linearity of the receiver system by comparing outputs derived from different tuning conditions. Furthermore, we measure the lunar filled beam efficiency of the telescope using the New Moon, and then derive the Absolute brightness Temperature of the Sun. The derived solar brightness Temperature is 7700 ± 310 K $7700 \pm 310~\mbox{K}$ at 115 GHz. The telescope beam pattern is modeled as a summation of three Gaussian functions and derived using the solar limb. The real shape of the Sun is determined via deconvolution of the beam pattern from the observed map. Such well-calibrated single-dish observations are important for high-resolution chromospheric studies because they provide the Absolute Temperature Scale that is lacking from interferometer observations.
G.r. Odette - One of the best experts on this subject based on the ideXlab platform.
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Assessment of irradiation embrittlement of the Eurofer97 steel after 590 MeV proton irradiation
Journal of Nuclear Materials, 2009Co-Authors: Philippe Spätig, G.r. Odette, R. Stoenescu, P. Mueller, D. GraggAbstract:The irradiation hardening of the Eurofer97 steel following 590 MeV proton irradiations was determined at three different irradiation Temperatures, 50 °C, 250 °C and 350 °C, and various doses up to about 1.3 displacement per atom. The dose and Temperature dependence of the irradiation hardening was characterized by a linear relationship between the irradiation hardening and the square root of the dose as: delta_yield_stress=k(T)dpa^1/2. Mini pre-cracked bend bar (1x1x16 mm3) were also tested in the lower ductile to brittle transition region before and after irradiation at 300 °C and 0.5 dpa. The effective fracture toughness-Temperature curves, Ke(T), were indexed on an Absolute Temperature Scale at To for Ke=100 MPa m1/2 for both the unirradiated and irradiated condition. The irradiation-induced Temperature shift delta_To of the Ke(T) curves yielded a coefficient Co, defined as Co=delta_To /delta_yield_stress, of about 0.53. For these low doses, helium effects could not be identified on the fracture properties.
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Cleavage fracture and irradiation embrittlement of fusion reactor alloys: mechanisms, multiScale models, toughness measurements and implications to structural integrity assessment
Journal of Nuclear Materials, 2003Co-Authors: G.r. Odette, Takuya Yamamoto, H. J. Rathbun, M.y. He, M. Hribernik, J.w. RensmanAbstract:We describe the highly efficient master curves–shifts (MC–ΔT) method to measure and apply cleavage fracture toughness, KJc(T), data and show that it is applicable to 9Cr martensitic steels. A reference Temperature, T0, indexes the invariant MC shape on an Absolute Temperature Scale. Then, T0 shifts (ΔT) are used to account for various effects of size and geometry, loading rate and irradiation embrittlement (ΔTi). The paper outlines a multiScale model, relating atomic to structural Scale fracture processes, that underpins the MC–ΔT method. At the atomic Scale, we propose that the intrinsic microarrest toughness, Kμ(T), of the body-centered cubic ferrite lattice dictates an invariant shape of the macroscopic KJc(T) curve. KJc(T) can be modeled in terms of the true stress–strain (σ–e) constitutive law, σ (T,ϵ), combined with a Temperature-dependent critical local stress, σ*(T) and stressed volume, V*. The local fracture properties, σ*(T)–V*, are governed by coarse-Scale brittle trigger particles and Kμ(T). Irradiation (and high strain rate) induced increases in the yield stress, Δσy, lead to ΔTi, with typical ΔTi/Δσy≈0.6±0.15 °C/MPa. However, ΔTi associated with decreases in σ* and V* can result from a number of potential non-hardening embrittlement (NHE) mechanisms, including a large amount of He on grain boundaries. Estimates based on available data suggest that this occurs at >500–700 appm bulk He. Hardening and NHE are synergistic, and can lead to very large ΔTi. NHE is signaled by large (>1 °C/MPa), or even negative, values of ΔTi/Δσy (for Δσy 1 and Δc/Δy≫1. Indeed, in some circumstances, the benefits of irradiation due to increases in Pc may more than offset the liabilities of the decreases in Δc.
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An integrated approach to assessing the fracture safe margins of fusion reactor structures
1996Co-Authors: G.r. OdetteAbstract:Design and operation of fusion reactor structures will require an appropriate data base closely coupled to a reliable failure analysis method to safely manage irradiation embrittlement. However, ongoing irradiation programs will not provide the information on embrittlement necessary to accomplish these objectives. A new engineering approach is proposed based on the concept of a master toughness-Temperature curve indexed on an Absolute Temperature Scale using shifts to account for variables such as size Scales, crack geometry and loading rates as well as embrittlement. While providing a simple practical engineering expedient, the proposed method can also be greatly enhanced by fundamental mechanism based models of fracture and embrittlement. Indeed, such understanding is required for the effective use of small specimen test methods, which is a integral element in developing the necessary data base.
Siavash H. Sohrab - One of the best experts on this subject based on the ideXlab platform.
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On a Scale-Invariant Model of Statistical Mechanics and the Laws of Thermodynamics
Journal of Energy Resources Technology-transactions of The Asme, 2016Co-Authors: Siavash H. SohrabAbstract:A Scale-invariant model of statistical mechanics is applied to describe modified forms of zeroth, first, second, and third laws of classical thermodynamics. Following Helmholtz, the total thermal energy of the thermodynamic system is decomposed into free heat U and latent heat pV suggesting the modified form of the first law of thermodynamics Q = H = U + pV. Following Boltzmann, entropy of ideal gas is expressed in terms of the number of Heisenberg–Kramers virtual oscillators as S = 4 Nk. Through introduction of stochastic definition of Planck and Boltzmann constants, Kelvin Absolute Temperature Scale T (degree K) is identified as a length Scale T (m) that is related to de Broglie wavelength of particle thermal oscillations. It is argued that rather than relating to the surface area of its horizon suggested by Bekenstein (1973, “Black Holes and Entropy,” Phys. Rev. D, 7(8), pp. 2333–2346), entropy of black hole should be related to its total thermal energy, namely, its enthalpy leading to S = 4Nk in exact agreement with the prediction of Major and Setter (2001, “Gravitational Statistical Mechanics: A Model,” Classical Quantum Gravity, 18, pp. 5125–5142).
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Some implications of the modified forms of the first and the second laws of thermodynamics and the variational principles in chemically reactive systems
2005Co-Authors: Siavash H. SohrabAbstract:The application of a Scale-invariant statistical theory of fields to statistical thermodynamics is discussed. Defining the Boltzmann constant as Kk = k = mk c =1.381×10-23 J/K, Kelvin Absolute Temperature Scale becomes a length Scale. The thermal equilibrium between matter and radiation fields is described. The modified definition of Temperature results in the speed of sound in atmosphere 358 m/s and a modified mechanical equivalent of heat equal to the universal gas constant J = Ro. The physical foundation of the first and the second laws of thermodynamics are described in terms of two new state variables defining the reversible heat Qrev = TS and the reversible work Wrev = PV. The variational principles in reactive systems are described in terms of an invariant Lagrangian defined as Lβ =Uβ = Qβ - Wβ + Gβ = Kβ - Πβ + Lβ-1.
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A Scale-Invariant Model of Statistical Mechanics and Modified Forms of the First and the Second Laws of Thermodynamics
International Journal of Thermal Sciences, 1999Co-Authors: Siavash H. SohrabAbstract:Abstract A Scale-invariant statistical theory of fields is presented that leads to invariant definition of density, velocity, Temperature, and pressure. The definition of Boltzmann constant is introduced as k k = k = m k ν k c = 1.381 · 10 −23 J·K −1 , suggesting that the Kelvin Absolute Temperature Scale is equivalent to a length Scale. Two new state variables called the reversible heat Q rev = TS and the reversible work W rev = PV are introduced. The modified forms of the first and second law of thermodynamics are presented. The microscopic definition of heat (work) is presented as the kinetic energy due to the random (peculiar) translational, rotational, and pulsational motions. The Gibbs free energy of an element at Scale β is identified as the total system energy at Scale (β − 1), thus leading to an invariant form of the first law of thermodynamics U β = Q β − W β + N eβ U β −1 .
Stephen White - One of the best experts on this subject based on the ideXlab platform.
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The Brightness Temperature of the Quiet Solar Chromosphere at 2.6 mm
Solar Physics, 2017Co-Authors: Kazumasa Iwai, Masumi Shimojo, Shinichiro Asayama, Tetsuhiro Minamidani, Stephen White, Timothy Bastian, Masao SaitoAbstract:The Absolute brightness Temperature of the Sun at millimeter wavelengths is an important diagnostic of the solar chromosphere. Because the Sun is so bright, measurement of this property usually involves the operation of telescopes under extreme conditions and requires a rigorous performance assessment of the telescope. In this study, we establish solar observation and calibration techniques at 2.6 mm wavelength for the Nobeyama 45 m telescope and accurately derive the Absolute solar brightness Temperature. We tune the superconductor–insulator–superconductor (SIS) receiver by inducing different bias voltages onto the SIS mixer to prevent saturation. Then, we examine the linearity of the receiver system by comparing outputs derived from different tuning conditions. Furthermore, we measure the lunar filled beam efficiency of the telescope using the New Moon, and then derive the Absolute brightness Temperature of the Sun. The derived solar brightness Temperature is 7700 ± 310 K $7700 \pm 310~\mbox{K}$ at 115 GHz. The telescope beam pattern is modeled as a summation of three Gaussian functions and derived using the solar limb. The real shape of the Sun is determined via deconvolution of the beam pattern from the observed map. Such well-calibrated single-dish observations are important for high-resolution chromospheric studies because they provide the Absolute Temperature Scale that is lacking from interferometer observations.
