The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Michael Riemer - One of the best experts on this subject based on the ideXlab platform.
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secondary circulation of tropical cyclones in vertical wind shear lagrangian diagnostic and pathways of Environmental Interaction
Journal of the Atmospheric Sciences, 2015Co-Authors: Michael Riemer, Frederic LaliberteAbstract:AbstractThis study introduces a Lagrangian diagnostic of the secondary circulation of tropical cyclones (TCs), here defined by those trajectories that contribute to latent heat release in the region of high inertial stability of the TC core. This definition accounts for prominent asymmetries and transient flow features. Trajectories are mapped from the three-dimensional physical space to the (two dimensional) entropy–temperature space. The mass flux vector in this space subsumes the thermodynamic characteristics of the secondary circulation. The Lagrangian diagnostic is then employed to further analyze the impact of vertical wind shear on TCs in previously published idealized numerical experiments. One focus of this analysis is the classification and quantitative depiction of different pathways of Environmental Interaction based on thermodynamic properties of trajectories at initial and end times. Confirming results from previous work, vertical shear significantly increases the intrusion of low–equivalent...
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simple kinematic models for the Environmental Interaction of tropical cyclones in vertical wind shear
Atmospheric Chemistry and Physics, 2011Co-Authors: Michael Riemer, Michael T MontgomeryAbstract:Abstract. A major impediment to the intensity forecast of tropical cyclones (TCs) is believed to be associated with the Interaction of TCs with dry Environmental air. However, the conditions under which pronounced TC-environment Interaction takes place are not well understood. As a step towards improving our understanding of this problem, we analyze here the flow topology of a TC immersed in an environment of vertical wind shear in an idealized, three-dimensional, convection-permitting numerical experiment. A set of distinct streamlines, the so-called manifolds, can be identified under the assumptions of steady and layer-wise horizontal flow. The manifolds are shown to divide the flow around the TC into distinct regions. The manifold structure in our numerical experiment is more complex than the well-known manifold structure of a non-divergent point vortex in uniform background flow. In particular, one manifold spirals inwards and ends in a limit cycle, a meso-scale dividing streamline encompassing the eyewall above the layer of strong inflow associated with surface friction and below the outflow layer in the upper troposphere. From the perspective of a steady and layer-wise horizontal flow model, the eyewall is well protected from the intrusion of Environmental air. In order for the Environmental air to intrude into the inner-core convection, time-dependent and/or vertical motions, which are prevalent in the TC inner-core, are necessary. Air with the highest values of moist-entropy resides within the limit cycle. This "moist envelope" is distorted considerably by the imposed vertical wind shear, and the shape of the moist envelope is closely related to the shape of the limit cycle. In a first approximation, the distribution of high- and low-θe air around the TC at low to mid-levels is governed by the stirring of convectively modified air by the steady, horizontal flow. Motivated by the results from the idealized numerical experiment, an analogue model based on a weakly divergent point vortex in background flow is formulated. The simple kinematic model captures the essence of many salient features of the manifold structure in the numerical experiment. A regime diagram representing realistic values of TC intensity and vertical wind shear can be constructed for the point-vortex model. The results indicate distinct scenarios of Environmental Interaction depending on the ratio of storm intensity and vertical-shear magnitude. Further implications of the new results derived from the manifold analysis for TCs in the real atmosphere are discussed.
Michael T Montgomery - One of the best experts on this subject based on the ideXlab platform.
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simple kinematic models for the Environmental Interaction of tropical cyclones in vertical wind shear
Atmospheric Chemistry and Physics, 2011Co-Authors: Michael Riemer, Michael T MontgomeryAbstract:Abstract. A major impediment to the intensity forecast of tropical cyclones (TCs) is believed to be associated with the Interaction of TCs with dry Environmental air. However, the conditions under which pronounced TC-environment Interaction takes place are not well understood. As a step towards improving our understanding of this problem, we analyze here the flow topology of a TC immersed in an environment of vertical wind shear in an idealized, three-dimensional, convection-permitting numerical experiment. A set of distinct streamlines, the so-called manifolds, can be identified under the assumptions of steady and layer-wise horizontal flow. The manifolds are shown to divide the flow around the TC into distinct regions. The manifold structure in our numerical experiment is more complex than the well-known manifold structure of a non-divergent point vortex in uniform background flow. In particular, one manifold spirals inwards and ends in a limit cycle, a meso-scale dividing streamline encompassing the eyewall above the layer of strong inflow associated with surface friction and below the outflow layer in the upper troposphere. From the perspective of a steady and layer-wise horizontal flow model, the eyewall is well protected from the intrusion of Environmental air. In order for the Environmental air to intrude into the inner-core convection, time-dependent and/or vertical motions, which are prevalent in the TC inner-core, are necessary. Air with the highest values of moist-entropy resides within the limit cycle. This "moist envelope" is distorted considerably by the imposed vertical wind shear, and the shape of the moist envelope is closely related to the shape of the limit cycle. In a first approximation, the distribution of high- and low-θe air around the TC at low to mid-levels is governed by the stirring of convectively modified air by the steady, horizontal flow. Motivated by the results from the idealized numerical experiment, an analogue model based on a weakly divergent point vortex in background flow is formulated. The simple kinematic model captures the essence of many salient features of the manifold structure in the numerical experiment. A regime diagram representing realistic values of TC intensity and vertical wind shear can be constructed for the point-vortex model. The results indicate distinct scenarios of Environmental Interaction depending on the ratio of storm intensity and vertical-shear magnitude. Further implications of the new results derived from the manifold analysis for TCs in the real atmosphere are discussed.
Yue Leon Guo - One of the best experts on this subject based on the ideXlab platform.
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prenatal perfluorooctanoic acid exposure and glutathione s transferase t1 m1 genotypes and their association with atopic dermatitis at 2 years of age
PLOS ONE, 2019Co-Authors: Huiju Wen, Shuli Wang, Pauchung Chen, Yue Leon GuoAbstract:Background Perfluoroalkyl substance (PFAS) exposure was found associated with atopic diseases. Atopic dermatitis (AD) is a childhood skin disorder. However, the effect of Interaction between PFASs and glutathione S-transferase (GST) T1/M1 genotype on AD remains unclear. Objective To investigate the association between gene-Environmental Interaction and childhood AD using a birth cohort study. Methods From 2001 to 2005, 1,264 mother–newborn pairs were recruited from eight Taiwanese maternity hospitals. PFAS levels and Genotypes were analysed from cord blood. Information on children’s health status including AD occurrence was obtained via phone interviews at 6 months and 2 years. Cord plasma concentrations of nine PFASs were measured via ultra-high performance liquid chromatography/tandem mass spectrometry. GSTT1/M1 was genotyped (null/present) via polymerase chain reaction. Environment-gene Interaction effects on AD were assessed using multiple logistic regression analysis. Results Overall, 839 mother–newborn pairs completed all measurements. The prevalence of ever having physician-diagnosed AD by 2 years of age was 5.4%. Among PFASs, perfluorooctanoic acid (PFOA) was positively associated with AD adjusted for potential confounders. After grouping PFOA levels into three groups: undetected, below and above the median in those with detected, children in above the median group who had the GSTT1-null, or GSTM1-null genotype exhibited a higher odds ratio for AD (OR [95%CI] = 3.45 [1.26–9.99] and 2.92 [1.12–7.91], respectively) as compared to the undetected group. Conclusions Our data demonstrated that in-utero PFOA exposure with GSTT1/M1 null genotype were associated with AD. Minimizing early-life PFAS exposure may help against AD development, especially in genetically susceptible individuals.
Frederic Laliberte - One of the best experts on this subject based on the ideXlab platform.
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secondary circulation of tropical cyclones in vertical wind shear lagrangian diagnostic and pathways of Environmental Interaction
Journal of the Atmospheric Sciences, 2015Co-Authors: Michael Riemer, Frederic LaliberteAbstract:AbstractThis study introduces a Lagrangian diagnostic of the secondary circulation of tropical cyclones (TCs), here defined by those trajectories that contribute to latent heat release in the region of high inertial stability of the TC core. This definition accounts for prominent asymmetries and transient flow features. Trajectories are mapped from the three-dimensional physical space to the (two dimensional) entropy–temperature space. The mass flux vector in this space subsumes the thermodynamic characteristics of the secondary circulation. The Lagrangian diagnostic is then employed to further analyze the impact of vertical wind shear on TCs in previously published idealized numerical experiments. One focus of this analysis is the classification and quantitative depiction of different pathways of Environmental Interaction based on thermodynamic properties of trajectories at initial and end times. Confirming results from previous work, vertical shear significantly increases the intrusion of low–equivalent...
Jan Babic - One of the best experts on this subject based on the ideXlab platform.
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Active Compliance Control Reduces Upper Body Effort in Exoskeleton-Supported Walking
IEEE Transactions on Human-Machine Systems, 2020Co-Authors: Barkan Ugurlu, Hironori Oshima, Emre Sariyildiz, Tatsuo Narikiyo, Jan BabicAbstract:This article presents a locomotion controller for lower limb exoskeletons so as to enable the combined robot and user system to exhibit compliant walking characteristics when interacting with the environment. This is of critical importance to reduce the excessive ground reaction forces during the walking task execution with the aim of improved Environmental Interaction capabilities. In robot-aided walking support for paraplegics, the user has to actively use his/her upper limbs via crutches to ensure overall balance. By virtue of this requisite, several issues may particularly arise during touchdown instants, e.g., upper body orientation fluctuates, shoulder joints are subject to excessive loading, and arms may need to exert extra forces to counterbalance these effects. In order to reduce the upper body effort via compliant locomotion, the controller is designed to manage the force/position tradeoff by using an admittance controller in each joint. For proof of concept, a series of exoskeleton-aided walking experiments were conducted with the participation of nine healthy volunteers, four of whom additionally walked on an irregular surface for further performance evaluation. The results suggest that the proposed locomotion controller is advantageous over conventional high-gain position tracking in decreasing undesired oscillatory torso motion and total arm force, adequately reducing the required upper body effort.