LIN TIAN - Academia.edu (original) (raw)

Papers by LIN TIAN

Journal of Atmospheric and Oceanic Technology, 2004

The 94-GHz (W band) Cloud Radar System (CRS) has been developed and flown on a NASA ER-2 highalti... more The 94-GHz (W band) Cloud Radar System (CRS) has been developed and flown on a NASA ER-2 highaltitude (20 km) aircraft. The CRS is a fully coherent, polarimetric Doppler radar that is capable of detecting clouds and precipitation from the surface up to the aircraft altitude in the lower stratosphere. The radar is especially well suited for cirrus cloud studies because of its high sensitivity and fine spatial resolution. This paper describes the CRS motivation, instrument design, specifications, calibration, and preliminary data from NASA's Cirrus Regional Study of Tropical Anvils and Cirrus Layers-Florida Area Cirrus Experiment (CRYS-TAL-FACE) field campaign. The unique combination of CRS with other sensors on the ER-2 provides an unprecedented opportunity to study cloud radiative effects on the global energy budget. CRS observations are being used to improve our knowledge of atmospheric scattering and attenuation characteristics at 94 GHz, and to provide datasets for algorithm implementation and validation for the upcoming NASA CloudSat mission that will use a 94-GHz spaceborne cloud radar to provide the first direct global survey of the vertical structure of cloud systems.

Journal of Applied Meteorology, 2001

A persistent, mesoscale region of intense eyewall convection contained within Hurricane Bonnie on... more A persistent, mesoscale region of intense eyewall convection contained within Hurricane Bonnie on 23 August 1998 is examined from multiple observations synthesized from the National Aeronautics and Space Administration ER-2 and DC-8 aircraft. The intense convection occurred late in the day as Bonnie was attaining its minimum central pressure and during a stage when the inner core featured a markedly asymmetric structure. The internal structure of this convective burst and its relationship to the warm core are presented using a synthesis of high-resolution satellite, aircraft radar, and in situ data. An exceptionally vigorous eyewall tower within the burst and penetrating to nearly 18 km is described. A second intense eyewall tower, adjacent to the eye, is shown to be associated with a mesoscale subsiding current of air, with vertical velocities on the order of several meters per second that descends at least 9 km and extends horizontally nearly 25 km into the eye interior. The subsidence is a much deeper and broader-scale feature than the convectively induced, symmetric overturning that commonly occurs on the upper-level flanks of convective towers in other tropical environments. The air supplying the deep current probably originates both at tropopause height and also from air detrained out of the adjacent updraft at midlevels. Strong downdrafts within the eye could not be associated with every hot tower. Whether this result was due to undersampling by aircraft or whether deep eye downdrafts are indeed sporadic, it is plausible that up to 3ЊC of midlevel eye warming observed in Bonnie may arise from one or more of these convectively induced episodes rather than as a result of a gradual sinking motion applied uniformly throughout the eye.

Bulletin of The American Meteorological Society, 2000

Journal of Atmospheric and Oceanic Technology, 2005

One challenge of using millimeter-wave radar for measuring clouds is achieving system calibration... more One challenge of using millimeter-wave radar for measuring clouds is achieving system calibration. The delicate nature of millimeter-wave components and the harsh environment in which they operate may cause undetected changes in the system response unless gular system calibration is performed. Scattering properties of the Ocean surface have been widely used as a calibration reference for airborne and spaceborne microwave sensors. However, at millimeter-wave frequencies, the Ocean surface backscattering mechanism is still not well understood, in part, due to the lack of experimental measuiements. During the Cirrus Regional Study of Tropical Anvils and Cirrus Layers-Florida Area Cirrus Experiment (CRYSTAL-FACE), measurements of Ocean surface backscattering were made using a 94-GHz (W-band) cloud radar onboard a NASA ER-2 high-altitude aircraft. The measurement set includes the normalized Ocean surface cross section over a range of the incidence angles under a variety of wind conditions. Analysis of the radar measurements shows good agreement with a quasi-specular scattering model. This unprecedented dataset enhances our knowledge about the Ocean surface scattering mechanism at 94 GHz. The results of this work support the proposition of using the Ocean surface as a calibration reference for d o m e millimeter-wave cloud radars and for the ongoing NASA Cloudsat mission, which will use a 94-GHz spacebome cloud radar for global cloud measurements.

This paper addresses motion control issues of flexible joint robot manipulators using joint torqu... more This paper addresses motion control issues of flexible joint robot manipulators using joint torque feedback. A two-stage control scheme consisting of a motion controller and a joint torque controller is established in a systematic way for the general n-link case. To deal with uncertainties in the robotic system, a robust adaptive control algorithm is developed assuming that all system parameters including the joint flexibility values are unknown except for some of their bounds. The system stability is analyzed via Lyapunov stability theory. The result has the distinct feature that no restriction of joint flexibility, nor exact knowledge of the parameters of rotor subsystem is required. The outcome is a useful framework for generalization of control methods previously developed for rigid robots. Simulation results verify the effectiveness of the proposed control methods

Nature Structural & Molecular Biology, 2004

The proteasome is the main ATP-dependent protease in eukaryotic cells and controls the concentrat... more The proteasome is the main ATP-dependent protease in eukaryotic cells and controls the concentration of many regulatory proteins in the cytosol and nucleus. Proteins are targeted to the proteasome by the covalent attachment of polyubiquitin chains. The ubiquitin modification serves as the proteasome recognition element but by itself is not sufficient for efficient degradation of folded proteins. We report that proteolysis of tightly folded proteins is accelerated greatly when an unstructured region is attached to the substrate. The unstructured region serves as the initiation site for degradation and is hydrolyzed first, after which the rest of the protein is digested sequentially. These results identify the initiation site as a novel component of the targeting signal, which is required to engage the proteasome unfolding machinery efficiently. The proteasome degrades a substrate by first binding to its ubiquitin modification and then initiating unfolding at an unstructured region.

Journal of Atmospheric and Oceanic Technology, 2004

The 94-GHz (W band) Cloud Radar System (CRS) has been developed and flown on a NASA ER-2 highalti... more The 94-GHz (W band) Cloud Radar System (CRS) has been developed and flown on a NASA ER-2 highaltitude (20 km) aircraft. The CRS is a fully coherent, polarimetric Doppler radar that is capable of detecting clouds and precipitation from the surface up to the aircraft altitude in the lower stratosphere. The radar is especially well suited for cirrus cloud studies because of its high sensitivity and fine spatial resolution. This paper describes the CRS motivation, instrument design, specifications, calibration, and preliminary data from NASA's Cirrus Regional Study of Tropical Anvils and Cirrus Layers-Florida Area Cirrus Experiment (CRYS-TAL-FACE) field campaign. The unique combination of CRS with other sensors on the ER-2 provides an unprecedented opportunity to study cloud radiative effects on the global energy budget. CRS observations are being used to improve our knowledge of atmospheric scattering and attenuation characteristics at 94 GHz, and to provide datasets for algorithm implementation and validation for the upcoming NASA CloudSat mission that will use a 94-GHz spaceborne cloud radar to provide the first direct global survey of the vertical structure of cloud systems.

Journal of Applied Meteorology, 2001

A persistent, mesoscale region of intense eyewall convection contained within Hurricane Bonnie on... more A persistent, mesoscale region of intense eyewall convection contained within Hurricane Bonnie on 23 August 1998 is examined from multiple observations synthesized from the National Aeronautics and Space Administration ER-2 and DC-8 aircraft. The intense convection occurred late in the day as Bonnie was attaining its minimum central pressure and during a stage when the inner core featured a markedly asymmetric structure. The internal structure of this convective burst and its relationship to the warm core are presented using a synthesis of high-resolution satellite, aircraft radar, and in situ data. An exceptionally vigorous eyewall tower within the burst and penetrating to nearly 18 km is described. A second intense eyewall tower, adjacent to the eye, is shown to be associated with a mesoscale subsiding current of air, with vertical velocities on the order of several meters per second that descends at least 9 km and extends horizontally nearly 25 km into the eye interior. The subsidence is a much deeper and broader-scale feature than the convectively induced, symmetric overturning that commonly occurs on the upper-level flanks of convective towers in other tropical environments. The air supplying the deep current probably originates both at tropopause height and also from air detrained out of the adjacent updraft at midlevels. Strong downdrafts within the eye could not be associated with every hot tower. Whether this result was due to undersampling by aircraft or whether deep eye downdrafts are indeed sporadic, it is plausible that up to 3ЊC of midlevel eye warming observed in Bonnie may arise from one or more of these convectively induced episodes rather than as a result of a gradual sinking motion applied uniformly throughout the eye.

Bulletin of The American Meteorological Society, 2000

Journal of Atmospheric and Oceanic Technology, 2005

One challenge of using millimeter-wave radar for measuring clouds is achieving system calibration... more One challenge of using millimeter-wave radar for measuring clouds is achieving system calibration. The delicate nature of millimeter-wave components and the harsh environment in which they operate may cause undetected changes in the system response unless gular system calibration is performed. Scattering properties of the Ocean surface have been widely used as a calibration reference for airborne and spaceborne microwave sensors. However, at millimeter-wave frequencies, the Ocean surface backscattering mechanism is still not well understood, in part, due to the lack of experimental measuiements. During the Cirrus Regional Study of Tropical Anvils and Cirrus Layers-Florida Area Cirrus Experiment (CRYSTAL-FACE), measurements of Ocean surface backscattering were made using a 94-GHz (W-band) cloud radar onboard a NASA ER-2 high-altitude aircraft. The measurement set includes the normalized Ocean surface cross section over a range of the incidence angles under a variety of wind conditions. Analysis of the radar measurements shows good agreement with a quasi-specular scattering model. This unprecedented dataset enhances our knowledge about the Ocean surface scattering mechanism at 94 GHz. The results of this work support the proposition of using the Ocean surface as a calibration reference for d o m e millimeter-wave cloud radars and for the ongoing NASA Cloudsat mission, which will use a 94-GHz spacebome cloud radar for global cloud measurements.

This paper addresses motion control issues of flexible joint robot manipulators using joint torqu... more This paper addresses motion control issues of flexible joint robot manipulators using joint torque feedback. A two-stage control scheme consisting of a motion controller and a joint torque controller is established in a systematic way for the general n-link case. To deal with uncertainties in the robotic system, a robust adaptive control algorithm is developed assuming that all system parameters including the joint flexibility values are unknown except for some of their bounds. The system stability is analyzed via Lyapunov stability theory. The result has the distinct feature that no restriction of joint flexibility, nor exact knowledge of the parameters of rotor subsystem is required. The outcome is a useful framework for generalization of control methods previously developed for rigid robots. Simulation results verify the effectiveness of the proposed control methods

Nature Structural & Molecular Biology, 2004

The proteasome is the main ATP-dependent protease in eukaryotic cells and controls the concentrat... more The proteasome is the main ATP-dependent protease in eukaryotic cells and controls the concentration of many regulatory proteins in the cytosol and nucleus. Proteins are targeted to the proteasome by the covalent attachment of polyubiquitin chains. The ubiquitin modification serves as the proteasome recognition element but by itself is not sufficient for efficient degradation of folded proteins. We report that proteolysis of tightly folded proteins is accelerated greatly when an unstructured region is attached to the substrate. The unstructured region serves as the initiation site for degradation and is hydrolyzed first, after which the rest of the protein is digested sequentially. These results identify the initiation site as a novel component of the targeting signal, which is required to engage the proteasome unfolding machinery efficiently. The proteasome degrades a substrate by first binding to its ubiquitin modification and then initiating unfolding at an unstructured region.