The Eliashberg theory of superconductivity accounts for the fundamental physics of conventional superconductors,including the retardation of the interaction and the Coulomb pseudopotential,to predict the critical temp...The Eliashberg theory of superconductivity accounts for the fundamental physics of conventional superconductors,including the retardation of the interaction and the Coulomb pseudopotential,to predict the critical temperature T_(c).McMillan,Allen,and Dynes derived approximate closed-form expressions for the critical temperature within this theory,which depends on the electron–phonon spectral functionα^(2)F(ω).Here we show that modern machine-learning techniques can substantially improve these formulae,accounting for more general shapes of theα^(2)F function.Using symbolic regression and the SISSO framework,together with a database of artificially generatedα^(2)F functions and numerical solutions of the Eliashberg equations,we derive a formula for T_(c)that performs as well as Allen–Dynes for low-T_(c)superconductors and substantially better for higher-T_(c)ones.This corrects the systematic underestimation of Tc while reproducing the physical constraints originally outlined by Allen and Dynes.This equation should replace the Allen–Dynes formula for the prediction of higher-temperature superconductors.展开更多
Experiments were conducted to investigate the forced convective heat transfer and flow friction of turbulent airflow in a rectangular duct with cross-ribs attached at the two principal walls in the Reynolds number ran...Experiments were conducted to investigate the forced convective heat transfer and flow friction of turbulent airflow in a rectangular duct with cross-ribs attached at the two principal walls in the Reynolds number range from 5000 to 40000. The effect of the rib cross angle (45° 60° 75° and the height (4 mm, 5 mm) of the cross-ribs on the forced convection and flow friction were tested. Non-dimensional correlations for the duct average Nusselt number and friction factor of cross-ribs duct were developed from the test data. Experiments were also conducted for the corresponding parallel ribs to compare their relative performance. The experimental results show that both of the convective heat transfer coefficient and friction factor were increased with cross-ribs, with 45°cross-ribs being the best. Compared with parallel ribs normal to the flow direction under identical flow rate and identical pumping power constraints, the cross-ribs can enhance heat transfer in the lower Reynolds number region, while展开更多
This paper evaluates the SIFOM-FVCOM system recently developed by the authors to simulate multiphysics coastal ocean flow phenomena, especially those at small scales. First, its formulation for buoyancy is examined wi...This paper evaluates the SIFOM-FVCOM system recently developed by the authors to simulate multiphysics coastal ocean flow phenomena, especially those at small scales. First, its formulation for buoyancy is examined with regard to solution accu- racy and computational efficiency. Then, the system is used to track particles in circulations in the Jamaica Bay, demonstrating that large-scale patterns of trajectories of fluid particles are sensitive to small-scales flows from which they are released. Finally, a simulation is presented to illustrate the SIFOM-FVCOM system＇s capability, which is beyond the reach of other existing models, to directly and simultaneously model large-scale storm surges as well as small-scale flow structures around bridge piers within the Hudson River during the Hurricane Sandy.展开更多
基金The work presented here was performed under the auspice of Basic Energy Sciences,United States Department of Energy,contract number DE-SC0020385.
文摘The Eliashberg theory of superconductivity accounts for the fundamental physics of conventional superconductors,including the retardation of the interaction and the Coulomb pseudopotential,to predict the critical temperature T_(c).McMillan,Allen,and Dynes derived approximate closed-form expressions for the critical temperature within this theory,which depends on the electron–phonon spectral functionα^(2)F(ω).Here we show that modern machine-learning techniques can substantially improve these formulae,accounting for more general shapes of theα^(2)F function.Using symbolic regression and the SISSO framework,together with a database of artificially generatedα^(2)F functions and numerical solutions of the Eliashberg equations,we derive a formula for T_(c)that performs as well as Allen–Dynes for low-T_(c)superconductors and substantially better for higher-T_(c)ones.This corrects the systematic underestimation of Tc while reproducing the physical constraints originally outlined by Allen and Dynes.This equation should replace the Allen–Dynes formula for the prediction of higher-temperature superconductors.
基金The work described in this paper has been supported by a grant from the Research Grants Council of the Hong Kong Special Administrative Region, China (Project No. PolyU 5156/99E).
文摘Experiments were conducted to investigate the forced convective heat transfer and flow friction of turbulent airflow in a rectangular duct with cross-ribs attached at the two principal walls in the Reynolds number range from 5000 to 40000. The effect of the rib cross angle (45° 60° 75° and the height (4 mm, 5 mm) of the cross-ribs on the forced convection and flow friction were tested. Non-dimensional correlations for the duct average Nusselt number and friction factor of cross-ribs duct were developed from the test data. Experiments were also conducted for the corresponding parallel ribs to compare their relative performance. The experimental results show that both of the convective heat transfer coefficient and friction factor were increased with cross-ribs, with 45°cross-ribs being the best. Compared with parallel ribs normal to the flow direction under identical flow rate and identical pumping power constraints, the cross-ribs can enhance heat transfer in the lower Reynolds number region, while
基金supported by NSF (Grant Nos. CMMI-1334551, DMS-1622459)PSC-CUNY+1 种基金Partial support also comes from NSFC (Grant Nos. 51239001, 51509023)SFMT (Grant No. 2015319825080)
文摘This paper evaluates the SIFOM-FVCOM system recently developed by the authors to simulate multiphysics coastal ocean flow phenomena, especially those at small scales. First, its formulation for buoyancy is examined with regard to solution accu- racy and computational efficiency. Then, the system is used to track particles in circulations in the Jamaica Bay, demonstrating that large-scale patterns of trajectories of fluid particles are sensitive to small-scales flows from which they are released. Finally, a simulation is presented to illustrate the SIFOM-FVCOM system＇s capability, which is beyond the reach of other existing models, to directly and simultaneously model large-scale storm surges as well as small-scale flow structures around bridge piers within the Hudson River during the Hurricane Sandy.
