The Experts below are selected from a list of 6798 Experts worldwide ranked by ideXlab platform
Zhaoyan Zhang - One of the best experts on this subject based on the ideXlab platform.
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Theory of shock wave propagation during laser ablation
Physical Review B, 2004Co-Authors: Zhaoyan Zhang, George GogosAbstract:Laser ablation consists of three coupled processes: (i) heat conduction within the solid, (ii) flow through a Discontinuity Layer (evaporation wave) attached to the solid surface, and (iii) shock wave expansion of the laser induced plume. In this paper, a one-dimensional solution for all three coupled processes is presented. The heat conduction and the evaporation wave are solved numerically. The shock wave expansion of the laser induced plume, however, is solved analytically, to our knowledge, for the first time; analytical solutions for the classic Riemann problem have been employed to solve the transient propagation of the strong shock wave. This model provides a sound theoretical basis for the analysis of the laser ablation process. The temperature, pressure, density, and velocity of the laser induced plume at different laser intensities, back temperatures, back pressures, and ambient gas species are calculated. The effects of the laser intensity, back temperature, back pressure, and ambient gas species are analyzed. The theoretical results provide insight into experimental results available in the literature.
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Theoretical Study of the Transient Shock Wave Propagation During Laser Ablation
Heat Transfer: Volume 1, 2003Co-Authors: Zhaoyan Zhang, George GogosAbstract:Laser ablation consists of three coupled processes: i) heat conduction within the solid, ii) flow through a Discontinuity Layer (evaporation wave) attached to the solid surface, and iii) shock wave expansion of the laser induced vapor. In this paper; a one-dimensional solution for all three coupled processes is presented. The heat conduction and the evaporation wave are solved numerically. The shock wave expansion of the laser induced vapor, how ever, is solved analytically for the first time Analytical solutions for the classic Riemann problem have been employed to solve the transient propagation of the strong shock wave. This model provides a sound theoretical basis for the analysis of the laser ablation process. The effects of the laser intensity, back temperature and back pressure are analyzed. The temperature pressure; density and velocity of the laser induced vapor are calculated and the results are discussed.Copyright © 2003 by ASME
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Numerical simulation of laser induced plasma during pulsed laser deposition
Journal of Applied Physics, 2001Co-Authors: Zhaoyan Zhang, Zhen-xue Han, George S. DulikravichAbstract:A numerical study of the laser induced evaporation and ionization process during pulsed laser deposition is presented. The process is separated into three domains: (i) conduction inside the solid, (ii) a Discontinuity Layer between solid and vapor, and (iii) expansion of high temperature vapor/plasma. A quasi-one-dimensional model is solved to predict the temperature field inside the solid. Mass, momentum, and energy are conserved across the Discontinuity Layer. Equations of mass, momentum, and energy conservation are solved simultaneously to provide boundary conditions for the expansion process. Euler equations are used to model the expansion of high temperature vapor/plasma. The Euler equations are integrated numerically using a Runge–Kutta scheme combined with flux vector splitting. The density, pressure, temperature, and velocity contours of the vapor phase are calculated and the results are analyzed.
George Gogos - One of the best experts on this subject based on the ideXlab platform.
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Theory of shock wave propagation during laser ablation
Physical Review B, 2004Co-Authors: Zhaoyan Zhang, George GogosAbstract:Laser ablation consists of three coupled processes: (i) heat conduction within the solid, (ii) flow through a Discontinuity Layer (evaporation wave) attached to the solid surface, and (iii) shock wave expansion of the laser induced plume. In this paper, a one-dimensional solution for all three coupled processes is presented. The heat conduction and the evaporation wave are solved numerically. The shock wave expansion of the laser induced plume, however, is solved analytically, to our knowledge, for the first time; analytical solutions for the classic Riemann problem have been employed to solve the transient propagation of the strong shock wave. This model provides a sound theoretical basis for the analysis of the laser ablation process. The temperature, pressure, density, and velocity of the laser induced plume at different laser intensities, back temperatures, back pressures, and ambient gas species are calculated. The effects of the laser intensity, back temperature, back pressure, and ambient gas species are analyzed. The theoretical results provide insight into experimental results available in the literature.
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Theoretical Study of the Transient Shock Wave Propagation During Laser Ablation
Heat Transfer: Volume 1, 2003Co-Authors: Zhaoyan Zhang, George GogosAbstract:Laser ablation consists of three coupled processes: i) heat conduction within the solid, ii) flow through a Discontinuity Layer (evaporation wave) attached to the solid surface, and iii) shock wave expansion of the laser induced vapor. In this paper; a one-dimensional solution for all three coupled processes is presented. The heat conduction and the evaporation wave are solved numerically. The shock wave expansion of the laser induced vapor, how ever, is solved analytically for the first time Analytical solutions for the classic Riemann problem have been employed to solve the transient propagation of the strong shock wave. This model provides a sound theoretical basis for the analysis of the laser ablation process. The effects of the laser intensity, back temperature and back pressure are analyzed. The temperature pressure; density and velocity of the laser induced vapor are calculated and the results are discussed.Copyright © 2003 by ASME
Jan G Hiddink - One of the best experts on this subject based on the ideXlab platform.
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impacts of bottom fishing on the sediment infaunal community and biogeochemistry of cohesive and non cohesive sediments
Limnology and Oceanography, 2016Co-Authors: Marija Sciberras, Ruth Parker, Claire Powell, Craig Robertson, Silke Kroger, Stefan G Bolam, Jan G HiddinkAbstract:Bottom-trawl fisheries are wide-spread and have large effects on benthic ecosystems.We investigate the effect of scallop dredging on sand and otter trawling on mud by measuring changes in the infaunal community and the biogeochemical processes which they mediate. We hypothesize that changes in biogeochemistry due to fishing will be larger in mud where macrofauna-mediated processes are expected to play a greater role, than in sand where hydrodynamics mediate the redox system. We sampled benthic infauna, sediment pore-water nutrients, oxygen, chlorophyll a (Chl a), apparent redox potential Discontinuity Layer, organic carbon and nitrogen content over a gradient of fishing intensity in sand and mud. The effects of fishing on biogeochemistry were stronger on mud than on sand, where biogeochemistry appeared to be more strongly influenced by tidal currents and waves. On mud, trawling increased sediment-surface Chl a and ammonium concentration beyond 5 cm depth, but decreased ammonium and silicate concentration in the upper sediment Layers. The effects of fauna and bioturbation potential on biogeochemistry were very limited in both mud and sand habitats. Our results suggests that otter trawling may be affecting organic-matter remineralization and nutrient cycling through sediment resuspension and burial of organic matter to depth rather than through the loss of bioturbation potential of the benthic community. In conclusion, our hypothesis that the effects of trawling on biogeochemistry are larger in mud is supported, but the hypothesis that these effects are mediated by changes in the infauna is not supported. These results imply that management of trawling on muddy sediments should have higher priority.
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Impacts of bottom fishing on the sediment infaunal community and biogeochemistry of cohesive and non‐cohesive sediments
Limnology and Oceanography, 2016Co-Authors: Marija Sciberras, Ruth Parker, Claire Powell, Silke Kroger, Stefan G Bolam, Craig M. Robertson, Jan G HiddinkAbstract:Bottom-trawl fisheries are wide-spread and have large effects on benthic ecosystems.We investigate the effect of scallop dredging on sand and otter trawling on mud by measuring changes in the infaunal community and the biogeochemical processes which they mediate. We hypothesize that changes in biogeochemistry due to fishing will be larger in mud where macrofauna-mediated processes are expected to play a greater role, than in sand where hydrodynamics mediate the redox system. We sampled benthic infauna, sediment pore-water nutrients, oxygen, chlorophyll a (Chl a), apparent redox potential Discontinuity Layer, organic carbon and nitrogen content over a gradient of fishing intensity in sand and mud. The effects of fishing on biogeochemistry were stronger on mud than on sand, where biogeochemistry appeared to be more strongly influenced by tidal currents and waves. On mud, trawling increased sediment-surface Chl a and ammonium concentration beyond 5 cm depth, but decreased ammonium and silicate concentration in the upper sediment Layers. The effects of fauna and bioturbation potential on biogeochemistry were very limited in both mud and sand habitats. Our results suggests that otter trawling may be affecting organic-matter remineralization and nutrient cycling through sediment resuspension and burial of organic matter to depth rather than through the loss of bioturbation potential of the benthic community. In conclusion, our hypothesis that the effects of trawling on biogeochemistry are larger in mud is supported, but the hypothesis that these effects are mediated by changes in the infauna is not supported. These results imply that management of trawling on muddy sediments should have higher priority.
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Impacts of Bottom Fishing on Sediment Biogeochemical and Biological Parameters in Cohesive and Non-cohesive Sediments
Limnology and Oceanography, 2016Co-Authors: Marija Sciberras, Ruth Parker, Silke Kroger, Stefan G Bolam, Craig M. Robertson, Claire F. Powell, Jan G HiddinkAbstract:Bottom-trawl fisheries are wide-spread and have large effects on benthic ecosystems.We investigate the effect of scallop dredging on sand and otter trawling on mud by measuring changes in the infaunal community and the biogeochemical processes which they mediate. We hypothesize that changes in biogeochemistry due to fishing will be larger in mud where macrofauna-mediated processes are expected to play a greater role, than in sand where hydrodynamics mediate the redox system. We sampled benthic infauna, sediment pore-water nutrients, oxygen, chlorophyll a (Chl a), apparent redox potential Discontinuity Layer, organic carbon and nitrogen content over a gradient of fishing intensity in sand and mud. The effects of fishing on biogeochemistry were stronger on mud than on sand, where biogeochemistry appeared to be more strongly influenced by tidal currents and waves. On mud, trawling increased sediment-surface Chl a and ammonium concentration beyond 5 cm depth, but decreased ammonium and silicate concentration in the upper sediment Layers. The effects of fauna and bioturbation potential on biogeochemistry were very limited in both mud and sand habitats. Our results suggests that otter trawling may be affecting organic-matter remineralization and nutrient cycling through sediment resuspension and burial of organic matter to depth rather than through the loss of bioturbation potential of the benthic community. In conclusion, our hypothesis that the effects of trawling on biogeochemistry are larger in mud is supported, but the hypothesis that these effects are mediated by changes in the infauna is not supported. These results imply that management of trawling on muddy sediments should have higher priority.
Marija Sciberras - One of the best experts on this subject based on the ideXlab platform.
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impacts of bottom fishing on the sediment infaunal community and biogeochemistry of cohesive and non cohesive sediments
Limnology and Oceanography, 2016Co-Authors: Marija Sciberras, Ruth Parker, Claire Powell, Craig Robertson, Silke Kroger, Stefan G Bolam, Jan G HiddinkAbstract:Bottom-trawl fisheries are wide-spread and have large effects on benthic ecosystems.We investigate the effect of scallop dredging on sand and otter trawling on mud by measuring changes in the infaunal community and the biogeochemical processes which they mediate. We hypothesize that changes in biogeochemistry due to fishing will be larger in mud where macrofauna-mediated processes are expected to play a greater role, than in sand where hydrodynamics mediate the redox system. We sampled benthic infauna, sediment pore-water nutrients, oxygen, chlorophyll a (Chl a), apparent redox potential Discontinuity Layer, organic carbon and nitrogen content over a gradient of fishing intensity in sand and mud. The effects of fishing on biogeochemistry were stronger on mud than on sand, where biogeochemistry appeared to be more strongly influenced by tidal currents and waves. On mud, trawling increased sediment-surface Chl a and ammonium concentration beyond 5 cm depth, but decreased ammonium and silicate concentration in the upper sediment Layers. The effects of fauna and bioturbation potential on biogeochemistry were very limited in both mud and sand habitats. Our results suggests that otter trawling may be affecting organic-matter remineralization and nutrient cycling through sediment resuspension and burial of organic matter to depth rather than through the loss of bioturbation potential of the benthic community. In conclusion, our hypothesis that the effects of trawling on biogeochemistry are larger in mud is supported, but the hypothesis that these effects are mediated by changes in the infauna is not supported. These results imply that management of trawling on muddy sediments should have higher priority.
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Impacts of bottom fishing on the sediment infaunal community and biogeochemistry of cohesive and non‐cohesive sediments
Limnology and Oceanography, 2016Co-Authors: Marija Sciberras, Ruth Parker, Claire Powell, Silke Kroger, Stefan G Bolam, Craig M. Robertson, Jan G HiddinkAbstract:Bottom-trawl fisheries are wide-spread and have large effects on benthic ecosystems.We investigate the effect of scallop dredging on sand and otter trawling on mud by measuring changes in the infaunal community and the biogeochemical processes which they mediate. We hypothesize that changes in biogeochemistry due to fishing will be larger in mud where macrofauna-mediated processes are expected to play a greater role, than in sand where hydrodynamics mediate the redox system. We sampled benthic infauna, sediment pore-water nutrients, oxygen, chlorophyll a (Chl a), apparent redox potential Discontinuity Layer, organic carbon and nitrogen content over a gradient of fishing intensity in sand and mud. The effects of fishing on biogeochemistry were stronger on mud than on sand, where biogeochemistry appeared to be more strongly influenced by tidal currents and waves. On mud, trawling increased sediment-surface Chl a and ammonium concentration beyond 5 cm depth, but decreased ammonium and silicate concentration in the upper sediment Layers. The effects of fauna and bioturbation potential on biogeochemistry were very limited in both mud and sand habitats. Our results suggests that otter trawling may be affecting organic-matter remineralization and nutrient cycling through sediment resuspension and burial of organic matter to depth rather than through the loss of bioturbation potential of the benthic community. In conclusion, our hypothesis that the effects of trawling on biogeochemistry are larger in mud is supported, but the hypothesis that these effects are mediated by changes in the infauna is not supported. These results imply that management of trawling on muddy sediments should have higher priority.
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Impacts of Bottom Fishing on Sediment Biogeochemical and Biological Parameters in Cohesive and Non-cohesive Sediments
Limnology and Oceanography, 2016Co-Authors: Marija Sciberras, Ruth Parker, Silke Kroger, Stefan G Bolam, Craig M. Robertson, Claire F. Powell, Jan G HiddinkAbstract:Bottom-trawl fisheries are wide-spread and have large effects on benthic ecosystems.We investigate the effect of scallop dredging on sand and otter trawling on mud by measuring changes in the infaunal community and the biogeochemical processes which they mediate. We hypothesize that changes in biogeochemistry due to fishing will be larger in mud where macrofauna-mediated processes are expected to play a greater role, than in sand where hydrodynamics mediate the redox system. We sampled benthic infauna, sediment pore-water nutrients, oxygen, chlorophyll a (Chl a), apparent redox potential Discontinuity Layer, organic carbon and nitrogen content over a gradient of fishing intensity in sand and mud. The effects of fishing on biogeochemistry were stronger on mud than on sand, where biogeochemistry appeared to be more strongly influenced by tidal currents and waves. On mud, trawling increased sediment-surface Chl a and ammonium concentration beyond 5 cm depth, but decreased ammonium and silicate concentration in the upper sediment Layers. The effects of fauna and bioturbation potential on biogeochemistry were very limited in both mud and sand habitats. Our results suggests that otter trawling may be affecting organic-matter remineralization and nutrient cycling through sediment resuspension and burial of organic matter to depth rather than through the loss of bioturbation potential of the benthic community. In conclusion, our hypothesis that the effects of trawling on biogeochemistry are larger in mud is supported, but the hypothesis that these effects are mediated by changes in the infauna is not supported. These results imply that management of trawling on muddy sediments should have higher priority.
Y. C. Whang - One of the best experts on this subject based on the ideXlab platform.
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Final Technical Report ''Double discontinuities in space plasma''
2004Co-Authors: Y. C. WhangAbstract:This research used high-resolution magnetic field data to examine the interior structures of MHD shocks in interplanetary space and in the magnetotail; we discovered that a slow-mode shock is often followed by an adjoining rotational Discontinuity Layer on the postshock side. The thickness of each Layer is of the order of a few ion inertial lengths. Such a compound structure is known as a double Discontinuity. When the magnetic field rotates by several degrees per ion inertial length inside a thin Layer, the Hall current term becomes important in the generalized Ohm's law. Steady state solutions based on the Hall-MHD theory have been obtained to show the merging of a rotational Layer and a slow shock Layer to form a compound structure like the observed double discontinuities.
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Theory and observation of double discontinuities
Nonlinear Processes in Geophysics, 2004Co-Authors: Y. C. WhangAbstract:Recent research using high-resolution magnetic field data to examine the interior structures of MHD shocks in interplanetary space and in the magnetotail led to a surprising discovery that a slow-mode shock is often followed by an adjoining rotational Discontinuity Layer on the postshock side. The thickness of each Layer is of the order of a few ion inertial lengths. Such a compound structure is known as a double Discontinuity. When the magnetic field rotates by several degrees per ion inertial length inside a thin Layer, the Hall current term becomes important in the generalized Ohm's law. Steady state solutions based on the Hall-MHD theory have been obtained to show the merging of a rotational Layer and a slow shock Layer to form a compound structure like the observed double discontinuities.
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Hall magnetohydrodynamics model of double discontinuities
Physics of Plasmas, 2002Co-Authors: Y. C. WhangAbstract:A double Discontinuity is a compound structure composed of a slow shock Layer and an adjoining rotational Discontinuity Layer on the postshock side. Since the Hall current effects become important as the magnetic field rotates by tens of degree over a thin rotational Layer, steady state solutions based on the Hall magnetohydrodynamics (MHD) theory can show the merging of a rotational Layer and a slow shock Layer to form the observed compound structure. This model uses a set of modified Rankine–Hugoniot relations to calculate the jump conditions between the upstream region and the interface between the two Layers, and uses the Hall-MHD equations to calculate the variations of the plasma and magnetic field in the rotational Layer in the downstream of the interface. Four series of solutions are presented to show the effect for each of four governing parameters on the structure of double discontinuities.
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Double discontinuities at the magnetotail plasma sheet-lobe boundary
Annales Geophysicae, 2001Co-Authors: Y. C. Whang, D. H. Fairfield, R. P. Lepping, Y. Saito, T. Mukai, James A. Slavin, Adam SzaboAbstract:A double Discontinuity is a compound structure composed of a slow shock Layer and an adjoining rotational Discontinuity Layer on the postshock side. We use high- resolution data from Geotail and Wind spacecraft to examine the interior structure within the finite thickness of the dis- continuity at the plasma sheet-lobe boundary and found that recognizable MHD structures at the boundary can be stand- alone slow shocks or double discontinuities. The plasma den- sity increases significantly and the magnetic field intensity decreases significantly across the interior of the slow shock Layer. Through the rotational Layer, the magnetic field ro- tates about the normal direction of the shock surface, as the plasma density and the magnetic field intensity remain nearly unchanged. The rotational angle can vary over a wide range. We notice that the observations of double discontinuities are no less frequent than the observations of stand-alone slow shocks. Identification of slow shocks and double disconti- nuities infers that plasma and magnetic field lines continu- ously move across the boundary surface from the lobe into the plasma sheet, and there is a conversion of magnetic field energy into plasma thermal energy through the slow shock Layer. The double discontinuities also allows for a rapid ro- tation of the postshock magnetic field lines immediately be- hind the shock Layer to accommodate the environment of the MHD flow in the plasma sheet region.
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Double Discontinuity: A compound structure of slow shock and rotational Discontinuity
Journal of Geophysical Research: Space Physics, 1998Co-Authors: Y. C. Whang, D. H. Fairfield, R. P. Lepping, Susumu Kokubun, J. Zhou, Adam Szabo, K. W. Ogilvie, R. J. FitzenreiterAbstract:This paper reports the observations of a compound structure in space plasma composed of a slow shock Layer and an adjoining rotational Discontinuity Layer on the postshock side. The compound structure looks like a new kind of MHD Discontinuity; it may be called a double Discontinuity. Two dual-spacecraft observations of double discontinuities using high-resolution magnetic field data were made in interplanetary space in 1995. The first one observed from Wind and IMP 8 is composed of a reversed slow shock and a rotational Discontinuity. The second one observed from Wind and Geotail is composed of a forward slow shock and a rotational Discontinuity. A double Discontinuity is a stable, large-scale solar wind structure. The thickness of the slow shock Layer is of a few ion inertial lengths. The flow in the preshock region has a low βi value and a large shock angle.