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Papers by wei leng

Research paper thumbnail of Yet another use for the laryngeal mask

Anaesthesia, 1992

Correspondence 175 administration (5-10s) did not produce this effect. So consistent is this find... more Correspondence 175 administration (5-10s) did not produce this effect. So consistent is this finding that one of us (W.D.M.) uses it as an additional confirmatory test of the correct placement of the intravenous cannula in the rat.

Research paper thumbnail of Viscous heating, adiabatic heating and energetic consistency in compressible mantle convection

Geophysical Journal International, 2008

Although it has been suggested that the total viscous heating, Qv, should be exactly balanced by ... more Although it has been suggested that the total viscous heating, Qv, should be exactly balanced by the total adiabatic heating, Qa, for compressible mantle convection, previous numerical studies show a significant imbalance of up to several percent between Qv and Qa for simple isoviscous compressible convection. The cause of this imbalance and its potential effects on more complicated convective systems remain largely unknown. In this study, we present an analysis to show that total viscous heating and adiabatic heating for compressible mantle convection with anelastic liquid approximation (ALA) and the Adams–Williamson equation of state are balanced out at any instant in time, and that the previously reported imbalance between Qv and Qa for numerical models with a truncated anelastic liquid approximation (TALA) is caused by neglecting the effect of the pressure on the buoyancy force. Although we only consider the Adams–Williamson equation of state in our analysis, our method can be used to check the energetic consistency for other forms of equation of state. We formulate numerical models of compressible mantle convection under both TALA and ALA formulations by modifying the Uzawa algorithm in Citcom code. Our numerical results confirm our analysis on the balance between total viscous heating and total adiabatic heating.

Research paper thumbnail of Constraints on thermochemical convection of the mantle from plume heat flux, plume excess temperature, and upper mantle temperature

Journal of Geophysical Research, 2006

1] Seismic and geochemical observations indicate a compositionally heterogeneous mantle in the lo... more 1] Seismic and geochemical observations indicate a compositionally heterogeneous mantle in the lower mantle, suggesting a layered mantle. The volume and composition of each layer, however, remain poorly constrained. This study seeks to constrain the layered mantle model from observed plume excess temperature, plume heat flux, and upper mantle temperature. Three-dimensional spherical models of whole mantle and layered mantle convection are computed for different Rayleigh number, internal heat generation, buoyancy number, and bottom layer thickness for layered mantle models. The model results show that these observations are controlled by internal heating rate in the layer overlying the thermal boundary layer from which mantle plumes are originated. To reproduce the observations, internal heating rate needs 6565% for whole mantle convection, but for layered mantle models, the internal heating rate for the top layer is 6560-65% for averaged bottom layer thicknesses <$1100 km. The heat flux at the core-mantle boundary (CMB) is constrained to be 12.6TWforwholemantleconvection.Forlayeredmantle,anupperboundontheCMBheatfluxis12.6 TW for whole mantle convection. For layered mantle, an upper bound on the CMB heat flux is 12.6TWforwholemantleconvection.Forlayeredmantle,anupperboundontheCMBheatfluxis14.4 TW. For mantle secular cooling rate of 80K/Ga,thecurrentstudysuggeststhatthetoplayerofalayeredmantleisrelativelythick(>2520km)andhasradiogenicheatgenerationrate>2.82A^10Aˋ12W/kgthatis>3timesofthatforthedepletedmantlesourceformid−oceanridgebasalts(DMM).ForthetoplayertohavetheradiogenicheatgenerationoftheDMM,mantlesecularcoolingrateneedstoexceed145K/Ga.ThecurrentstudyalsoshowsthatplumetemperatureintheuppermantleisabouthalfoftheCMBtemperatureforwholemantleconvectionor80 K/Ga, the current study suggests that the top layer of a layered mantle is relatively thick (>2520 km) and has radiogenic heat generation rate >2.82 Â 10 À12 W/kg that is >3 times of that for the depleted mantle source for mid-ocean ridge basalts (DMM). For the top layer to have the radiogenic heat generation of the DMM, mantle secular cooling rate needs to exceed 145 K/Ga. The current study also shows that plume temperature in the upper mantle is about half of the CMB temperature for whole mantle convection or 80K/Ga,thecurrentstudysuggeststhatthetoplayerofalayeredmantleisrelativelythick(>2520km)andhasradiogenicheatgenerationrate>2.82A^10Aˋ12W/kgthatis>3timesofthatforthedepletedmantlesourceformid−oceanridgebasalts(DMM).ForthetoplayertohavetheradiogenicheatgenerationoftheDMM,mantlesecularcoolingrateneedstoexceed145K/Ga.ThecurrentstudyalsoshowsthatplumetemperatureintheuppermantleisabouthalfoftheCMBtemperatureforwholemantleconvectionor0.6 of temperature at compositional boundary for a layered mantle, independent of internal heating rate and Rayleigh number. Finally, the model calculations confirm that mantle plumes accounts for the majority ($80%) of CMB heat flux in whole mantle convection models. However, plume heat flux decreases significantly by as much as a factor of 3, as plumes ascend through the mantle to the upper mantle, owing to the adiabatic and possibly diffusive cooling of the plumes and owing to slight ($180 K) subadiabaticity in mantle geotherm. Citation: Zhong, S. (2006), Constraints on thermochemical convection of the mantle from plume heat flux, plume excess temperature, and upper mantle temperature,

Research paper thumbnail of Controls on plume heat flux and plume excess temperature

Journal of Geophysical Research, 2008

1] Plume heat flux and plume excess temperature in the upper mantle inferred from surface observa... more 1] Plume heat flux and plume excess temperature in the upper mantle inferred from surface observations may pose important constraints on the heat flux from the core and mantle internal heating rate. This study examined the relationship between plume heat flux Q p , core-mantle boundary (CMB) heat flux Q cmb and plume excess temperature DT plume in thermal convection using both numerical modeling and theoretical analysis. 3-D regional spherical models of mantle convection were computed with high resolution and for different Rayleigh number, internal heat generation rate, viscosity structures and dissipation number. An analytic model was developed for variations in Q p and DT plume with depth. The results can be summarized as following.

Research paper thumbnail of A community benchmark for 2-D Cartesian compressible convection in the Earth's mantle

Geophysical Journal International, 2010

Benchmark comparisons are an essential tool to verify the accuracy and validity of computational ... more Benchmark comparisons are an essential tool to verify the accuracy and validity of computational approaches to mantle convection. Six 2D Cartesian compressible convection codes are compared for steady-state constant and temperature-dependent viscosity cases as well as time-dependent constant viscosity cases. In general we find good agreement between all codes when comparing average flow characteristics such as Nusselt number and root-mean-square velocity. At Rayleigh numbers near 10 6 and dissipation numbers between 0 and 2, the results differ by approximately 1%. Differences in discretization and use of finite volumes vs. finite elements dominate the differences. There is a small systematic difference between the use of the anelastic liquid approximation compared to that of the truncated anelastic liquid approximation. In determining the onset of time-dependence, there was less agreement between the codes with a spread in the Rayleigh number where the first bifurcation occurs ranging from 7.79 × 10 5 to 1.05 × 10 6 .

Research paper thumbnail of Yet another use for the laryngeal mask

Anaesthesia, 1992

Correspondence 175 administration (5-10s) did not produce this effect. So consistent is this find... more Correspondence 175 administration (5-10s) did not produce this effect. So consistent is this finding that one of us (W.D.M.) uses it as an additional confirmatory test of the correct placement of the intravenous cannula in the rat.

Research paper thumbnail of Viscous heating, adiabatic heating and energetic consistency in compressible mantle convection

Geophysical Journal International, 2008

Although it has been suggested that the total viscous heating, Qv, should be exactly balanced by ... more Although it has been suggested that the total viscous heating, Qv, should be exactly balanced by the total adiabatic heating, Qa, for compressible mantle convection, previous numerical studies show a significant imbalance of up to several percent between Qv and Qa for simple isoviscous compressible convection. The cause of this imbalance and its potential effects on more complicated convective systems remain largely unknown. In this study, we present an analysis to show that total viscous heating and adiabatic heating for compressible mantle convection with anelastic liquid approximation (ALA) and the Adams–Williamson equation of state are balanced out at any instant in time, and that the previously reported imbalance between Qv and Qa for numerical models with a truncated anelastic liquid approximation (TALA) is caused by neglecting the effect of the pressure on the buoyancy force. Although we only consider the Adams–Williamson equation of state in our analysis, our method can be used to check the energetic consistency for other forms of equation of state. We formulate numerical models of compressible mantle convection under both TALA and ALA formulations by modifying the Uzawa algorithm in Citcom code. Our numerical results confirm our analysis on the balance between total viscous heating and total adiabatic heating.

Research paper thumbnail of Constraints on thermochemical convection of the mantle from plume heat flux, plume excess temperature, and upper mantle temperature

Journal of Geophysical Research, 2006

1] Seismic and geochemical observations indicate a compositionally heterogeneous mantle in the lo... more 1] Seismic and geochemical observations indicate a compositionally heterogeneous mantle in the lower mantle, suggesting a layered mantle. The volume and composition of each layer, however, remain poorly constrained. This study seeks to constrain the layered mantle model from observed plume excess temperature, plume heat flux, and upper mantle temperature. Three-dimensional spherical models of whole mantle and layered mantle convection are computed for different Rayleigh number, internal heat generation, buoyancy number, and bottom layer thickness for layered mantle models. The model results show that these observations are controlled by internal heating rate in the layer overlying the thermal boundary layer from which mantle plumes are originated. To reproduce the observations, internal heating rate needs 6565% for whole mantle convection, but for layered mantle models, the internal heating rate for the top layer is 6560-65% for averaged bottom layer thicknesses <$1100 km. The heat flux at the core-mantle boundary (CMB) is constrained to be 12.6TWforwholemantleconvection.Forlayeredmantle,anupperboundontheCMBheatfluxis12.6 TW for whole mantle convection. For layered mantle, an upper bound on the CMB heat flux is 12.6TWforwholemantleconvection.Forlayeredmantle,anupperboundontheCMBheatfluxis14.4 TW. For mantle secular cooling rate of 80K/Ga,thecurrentstudysuggeststhatthetoplayerofalayeredmantleisrelativelythick(>2520km)andhasradiogenicheatgenerationrate>2.82A^10Aˋ12W/kgthatis>3timesofthatforthedepletedmantlesourceformid−oceanridgebasalts(DMM).ForthetoplayertohavetheradiogenicheatgenerationoftheDMM,mantlesecularcoolingrateneedstoexceed145K/Ga.ThecurrentstudyalsoshowsthatplumetemperatureintheuppermantleisabouthalfoftheCMBtemperatureforwholemantleconvectionor80 K/Ga, the current study suggests that the top layer of a layered mantle is relatively thick (>2520 km) and has radiogenic heat generation rate >2.82 Â 10 À12 W/kg that is >3 times of that for the depleted mantle source for mid-ocean ridge basalts (DMM). For the top layer to have the radiogenic heat generation of the DMM, mantle secular cooling rate needs to exceed 145 K/Ga. The current study also shows that plume temperature in the upper mantle is about half of the CMB temperature for whole mantle convection or 80K/Ga,thecurrentstudysuggeststhatthetoplayerofalayeredmantleisrelativelythick(>2520km)andhasradiogenicheatgenerationrate>2.82A^10Aˋ12W/kgthatis>3timesofthatforthedepletedmantlesourceformid−oceanridgebasalts(DMM).ForthetoplayertohavetheradiogenicheatgenerationoftheDMM,mantlesecularcoolingrateneedstoexceed145K/Ga.ThecurrentstudyalsoshowsthatplumetemperatureintheuppermantleisabouthalfoftheCMBtemperatureforwholemantleconvectionor0.6 of temperature at compositional boundary for a layered mantle, independent of internal heating rate and Rayleigh number. Finally, the model calculations confirm that mantle plumes accounts for the majority ($80%) of CMB heat flux in whole mantle convection models. However, plume heat flux decreases significantly by as much as a factor of 3, as plumes ascend through the mantle to the upper mantle, owing to the adiabatic and possibly diffusive cooling of the plumes and owing to slight ($180 K) subadiabaticity in mantle geotherm. Citation: Zhong, S. (2006), Constraints on thermochemical convection of the mantle from plume heat flux, plume excess temperature, and upper mantle temperature,

Research paper thumbnail of Controls on plume heat flux and plume excess temperature

Journal of Geophysical Research, 2008

1] Plume heat flux and plume excess temperature in the upper mantle inferred from surface observa... more 1] Plume heat flux and plume excess temperature in the upper mantle inferred from surface observations may pose important constraints on the heat flux from the core and mantle internal heating rate. This study examined the relationship between plume heat flux Q p , core-mantle boundary (CMB) heat flux Q cmb and plume excess temperature DT plume in thermal convection using both numerical modeling and theoretical analysis. 3-D regional spherical models of mantle convection were computed with high resolution and for different Rayleigh number, internal heat generation rate, viscosity structures and dissipation number. An analytic model was developed for variations in Q p and DT plume with depth. The results can be summarized as following.

Research paper thumbnail of A community benchmark for 2-D Cartesian compressible convection in the Earth's mantle

Geophysical Journal International, 2010

Benchmark comparisons are an essential tool to verify the accuracy and validity of computational ... more Benchmark comparisons are an essential tool to verify the accuracy and validity of computational approaches to mantle convection. Six 2D Cartesian compressible convection codes are compared for steady-state constant and temperature-dependent viscosity cases as well as time-dependent constant viscosity cases. In general we find good agreement between all codes when comparing average flow characteristics such as Nusselt number and root-mean-square velocity. At Rayleigh numbers near 10 6 and dissipation numbers between 0 and 2, the results differ by approximately 1%. Differences in discretization and use of finite volumes vs. finite elements dominate the differences. There is a small systematic difference between the use of the anelastic liquid approximation compared to that of the truncated anelastic liquid approximation. In determining the onset of time-dependence, there was less agreement between the codes with a spread in the Rayleigh number where the first bifurcation occurs ranging from 7.79 × 10 5 to 1.05 × 10 6 .