Our previous 2-D simulations have revealed the linear and nonlinear properties of mode conversion... more Our previous 2-D simulations have revealed the linear and nonlinear properties of mode conversion from incident fast-mode compressional waves to short wavelength (k⊥ρi ~ 1) kinetic Alfven waves (KAWs) at the magnetopause near the Alfven resonance surface, for simple cases in which the background magnetic fields on both sides of the current layer are parallel, corresponding to a northward interplanetary magnetic field. In this study, we further broaden our investigation to include (1) the effects of magnetic field rotation across the current layer and (2) the 3-D effects under various k vectors of the incident waves using a 3-D hybrid simulation. In the cases in which the magnetic field changes direction from the magnetosheath to the magnetosphere, there may exist two to three resonance points satisfying the Alfven resonance condition ω2=k∥2VA2(1-ω2/Ωi2), where ω is the wave frequency, VA is the local Alfven speed, and Ωi is the ion gyrofrequency. These waves radiate in opposite directions away from the resonance locations (in the case with two resonances) and wave energy can also be trapped in a leaky potential well in the case where there are three resonances. The wave absorption rate and the ion heating in the mode conversion processes are presented. Due to the 3-D effects, modes with finite ky's are generated while the initial waves propagate in the (kx, kz) plane. Harmonics of the driver frequency are generated in the the resulting KAWs, and meanwhile modes with strong k⊥ are produced. The nonlinear physics of 3-D mode conversion are discussed.
Journal of Mechanical Science and Technology, 2005
A vehicle cruise control strategy designed based on human drivers driving characteristics has bee... more A vehicle cruise control strategy designed based on human drivers driving characteristics has been investigated. Human drivers driving patterns have been investigated using vehicle driving test data obtained from 125 participants. The control algorithm has been designed to incorporate the driving characteristics of the human drivers and to achieve natural vehicle behavior of the controlled vehicle that would feel comfortable to the human driver. Vehicle following characteristics of the cruise controlled vehicle have been investigated using real-world vehicle driving test data and a validated simulation package.
We consider the problem of constraining a particle to a submanifold Sigma of configuration space ... more We consider the problem of constraining a particle to a submanifold Sigma of configuration space using a sequence of increasing potentials. We compare the classical and quantum versions of this procedure. This leads to new results in both cases: an unbounded energy theorem in the classical case, and a quantum averaging theorem. Our two step approach, consisting of an expansion in a dilation parameter, followed by averaging in normal directions, emphasizes the role of the normal bundle of Sigma, and shows when the limiting phase space will be larger (or different) than expected.
We consider the problem of constraining a particle to a smooth compact submanifold Σ of configura... more We consider the problem of constraining a particle to a smooth compact submanifold Σ of configuration space using a sequence of increasing potentials. We compare the classical and quantum versions of this procedure. This leads to new results in both cases: an unbounded energy theorem in the classical case, and a quantum averaging theorem. Our two step approach, consisting of an expansion in a dilation parameter, followed by averaging in normal directions, emphasizes the role of the normal bundle of Σ, and shows when the limiting phase space will be larger (or different) than expected.
Regional environmental change can be assessed using remote sensing in two ways: by looking for tr... more Regional environmental change can be assessed using remote sensing in two ways: by looking for trends in image time series in terms of spectral indices, like the normalized difference vegetation index (NDVI), or through post-classification change analysis to identify land cover change (LCC). Here we demonstrate the efficacy of combined trend-LCC analysis using the Northern Eurasian grain belt (NEGB) and Aral Basin (AB) as examples. NDVI time series from 2001-2008 were derived from 500m MODIS NBAR 8-d composites spanning the growing season from March to October of each year. LCC analysis was based on the 500m MODIS Global Land Cover product for the years 2001 and 2008. Seasonal Kendall trend tests showed, on a per-pixel basis, that statistically significant (p<0.05) NDVI trends were largely negative, with declining seasonal NDVI covering 57% of the NEGB’s land area and 15% of the AB. Among pixels exhibiting negative NDVI trends, we found elevated LCC rates (relative to pixels exhibiting no trend) from: (1) cropland mosaic to pure cropland in the northern portion of the NEGB, largely in Russia (RU); (2) cropland to grassland in the southern portion of the NEGB, largely in Kazakhstan (KZ); (3) cropland to grassland, and shrub to grassland, in the AB. Statistically significant (p<0.05) positive NDVI trends were rare, covering less than 1% of the NEGB and AB. Among pixels exhibiting positive NDVI trends, we found elevated LCC rates from: (1) cropland to cropland mosaic in relatively small clusters of pixels in the northern NEGB, mostly in RU; (2) grassland to cropland in the southern NEGB, largely in KZ, and also in small clusters; (3) grassland to cropland (largely along the Amu Darya river), in addition to more widespread conversion of grassland and barren classes to shrub, in the AB. In the NEGB, the overall direction of regional change was toward agricultural de-intensification in KZ, likely reflecting persistent drought, in contrast with agricultural intensification in RU - perhaps due to overriding effects of socioeconomic forces, relative to climatic drivers, on land use decisions in RU. In the AB, we find agricultural intensification (grassland to cropland conversion) associated with positive NDVI trends; concentration of positive trends along the Amu Darya in Karakalpakstan suggests an expansion of irrigation. We also find both shrub decline and shrub encroachment in the AB, with likely effects on ecosystem function reflected in negative NDVI trends (declining GPP) where shrubs are declining and positive NDVI trends (increasing GPP) where shrubs are increasing. In sum, LCC analysis complements NDVI trend analyses. LCC analysis focuses on discrete, abrupt, and principally human-caused change. NDVI trend analysis is better suited to identifying continuous, gradual change, primarily driven by climatic conditions. However, land surface changes are both discrete and continuous, depending on perspective, and can be mutually reinforcing. Here we find that LCC results inform our interpretation of NDVI trends and vice versa. Each analysis, alone, provides an incomplete picture of the complexities of land surface change.
The changes in abundance and composition experienced by phytoplankton communities in lakes and re... more The changes in abundance and composition experienced by phytoplankton communities in lakes and reservoirs occur in response to variations in the physical (light climate or energy) and the chemical (nutrient availability or resources) constraints for algal growth. Mediterranean reservoirs are very dynamic systems, subject to frequent changes in the physical environment as a result of water management operations, which suggests that phytoplankton communities might also undergo frequent changes. The phytoplankton community composition, abundance and seasonal dynamics of El Gergal, a medium-size Mediterranean reservoir, is analyzed and interpreted in terms of changes in the nutrient-energy balance. It is demonstrated that the seasonal scale changes in the physical environment trigger the seasonal predictable autogenic dynamics of the phytoplankton community. In addition, frequent short-term external perturbations of the physical environment may also induce allogenic shifts and reversions in the succession. The physical changes occur mainly as a result of variations in the outflows. Results are discussed in terms of phytoplankton functional groups life cycle strategies and water quality management.
Our previous 2-D simulations have revealed the linear and nonlinear properties of mode conversion... more Our previous 2-D simulations have revealed the linear and nonlinear properties of mode conversion from incident fast-mode compressional waves to short wavelength (k⊥ρi ~ 1) kinetic Alfven waves (KAWs) at the magnetopause near the Alfven resonance surface, for simple cases in which the background magnetic fields on both sides of the current layer are parallel, corresponding to a northward interplanetary magnetic field. In this study, we further broaden our investigation to include (1) the effects of magnetic field rotation across the current layer and (2) the 3-D effects under various k vectors of the incident waves using a 3-D hybrid simulation. In the cases in which the magnetic field changes direction from the magnetosheath to the magnetosphere, there may exist two to three resonance points satisfying the Alfven resonance condition ω2=k∥2VA2(1-ω2/Ωi2), where ω is the wave frequency, VA is the local Alfven speed, and Ωi is the ion gyrofrequency. These waves radiate in opposite directions away from the resonance locations (in the case with two resonances) and wave energy can also be trapped in a leaky potential well in the case where there are three resonances. The wave absorption rate and the ion heating in the mode conversion processes are presented. Due to the 3-D effects, modes with finite ky's are generated while the initial waves propagate in the (kx, kz) plane. Harmonics of the driver frequency are generated in the the resulting KAWs, and meanwhile modes with strong k⊥ are produced. The nonlinear physics of 3-D mode conversion are discussed.
Journal of Mechanical Science and Technology, 2005
A vehicle cruise control strategy designed based on human drivers driving characteristics has bee... more A vehicle cruise control strategy designed based on human drivers driving characteristics has been investigated. Human drivers driving patterns have been investigated using vehicle driving test data obtained from 125 participants. The control algorithm has been designed to incorporate the driving characteristics of the human drivers and to achieve natural vehicle behavior of the controlled vehicle that would feel comfortable to the human driver. Vehicle following characteristics of the cruise controlled vehicle have been investigated using real-world vehicle driving test data and a validated simulation package.
We consider the problem of constraining a particle to a submanifold Sigma of configuration space ... more We consider the problem of constraining a particle to a submanifold Sigma of configuration space using a sequence of increasing potentials. We compare the classical and quantum versions of this procedure. This leads to new results in both cases: an unbounded energy theorem in the classical case, and a quantum averaging theorem. Our two step approach, consisting of an expansion in a dilation parameter, followed by averaging in normal directions, emphasizes the role of the normal bundle of Sigma, and shows when the limiting phase space will be larger (or different) than expected.
We consider the problem of constraining a particle to a smooth compact submanifold Σ of configura... more We consider the problem of constraining a particle to a smooth compact submanifold Σ of configuration space using a sequence of increasing potentials. We compare the classical and quantum versions of this procedure. This leads to new results in both cases: an unbounded energy theorem in the classical case, and a quantum averaging theorem. Our two step approach, consisting of an expansion in a dilation parameter, followed by averaging in normal directions, emphasizes the role of the normal bundle of Σ, and shows when the limiting phase space will be larger (or different) than expected.
Regional environmental change can be assessed using remote sensing in two ways: by looking for tr... more Regional environmental change can be assessed using remote sensing in two ways: by looking for trends in image time series in terms of spectral indices, like the normalized difference vegetation index (NDVI), or through post-classification change analysis to identify land cover change (LCC). Here we demonstrate the efficacy of combined trend-LCC analysis using the Northern Eurasian grain belt (NEGB) and Aral Basin (AB) as examples. NDVI time series from 2001-2008 were derived from 500m MODIS NBAR 8-d composites spanning the growing season from March to October of each year. LCC analysis was based on the 500m MODIS Global Land Cover product for the years 2001 and 2008. Seasonal Kendall trend tests showed, on a per-pixel basis, that statistically significant (p<0.05) NDVI trends were largely negative, with declining seasonal NDVI covering 57% of the NEGB’s land area and 15% of the AB. Among pixels exhibiting negative NDVI trends, we found elevated LCC rates (relative to pixels exhibiting no trend) from: (1) cropland mosaic to pure cropland in the northern portion of the NEGB, largely in Russia (RU); (2) cropland to grassland in the southern portion of the NEGB, largely in Kazakhstan (KZ); (3) cropland to grassland, and shrub to grassland, in the AB. Statistically significant (p<0.05) positive NDVI trends were rare, covering less than 1% of the NEGB and AB. Among pixels exhibiting positive NDVI trends, we found elevated LCC rates from: (1) cropland to cropland mosaic in relatively small clusters of pixels in the northern NEGB, mostly in RU; (2) grassland to cropland in the southern NEGB, largely in KZ, and also in small clusters; (3) grassland to cropland (largely along the Amu Darya river), in addition to more widespread conversion of grassland and barren classes to shrub, in the AB. In the NEGB, the overall direction of regional change was toward agricultural de-intensification in KZ, likely reflecting persistent drought, in contrast with agricultural intensification in RU - perhaps due to overriding effects of socioeconomic forces, relative to climatic drivers, on land use decisions in RU. In the AB, we find agricultural intensification (grassland to cropland conversion) associated with positive NDVI trends; concentration of positive trends along the Amu Darya in Karakalpakstan suggests an expansion of irrigation. We also find both shrub decline and shrub encroachment in the AB, with likely effects on ecosystem function reflected in negative NDVI trends (declining GPP) where shrubs are declining and positive NDVI trends (increasing GPP) where shrubs are increasing. In sum, LCC analysis complements NDVI trend analyses. LCC analysis focuses on discrete, abrupt, and principally human-caused change. NDVI trend analysis is better suited to identifying continuous, gradual change, primarily driven by climatic conditions. However, land surface changes are both discrete and continuous, depending on perspective, and can be mutually reinforcing. Here we find that LCC results inform our interpretation of NDVI trends and vice versa. Each analysis, alone, provides an incomplete picture of the complexities of land surface change.
The changes in abundance and composition experienced by phytoplankton communities in lakes and re... more The changes in abundance and composition experienced by phytoplankton communities in lakes and reservoirs occur in response to variations in the physical (light climate or energy) and the chemical (nutrient availability or resources) constraints for algal growth. Mediterranean reservoirs are very dynamic systems, subject to frequent changes in the physical environment as a result of water management operations, which suggests that phytoplankton communities might also undergo frequent changes. The phytoplankton community composition, abundance and seasonal dynamics of El Gergal, a medium-size Mediterranean reservoir, is analyzed and interpreted in terms of changes in the nutrient-energy balance. It is demonstrated that the seasonal scale changes in the physical environment trigger the seasonal predictable autogenic dynamics of the phytoplankton community. In addition, frequent short-term external perturbations of the physical environment may also induce allogenic shifts and reversions in the succession. The physical changes occur mainly as a result of variations in the outflows. Results are discussed in terms of phytoplankton functional groups life cycle strategies and water quality management.
Uploads