713 research outputs found
Multiobjective gas turbine engine controller design using genetic algorithms
No full textThis paper describes the use of multiobjective genetic algorithms (MOGAs) in the design of a multivariable control system for a gas turbine engine. The mechanisms employed to facilitate multiobjective search with the genetic algorithm are described with the aid of an example. It is shown that the MOGA confers a number of advantages over conventional multiobjective optimization methods by evolving a family of Pareto-optimal solutions rather than a single solution estimate. This allows the engineer to examine the trade-offs between the different design objectives and configurations during the course of an optimization. In addition, the paper demonstrates how the genetic algorithm can be used to search in both controller structure and parameter space thereby offering a potentially more general approach to optimization in controller design than traditional numerical methods. While the example in the paper deals with control system design, the approach described can be expected to be applicable to more general problems in the fields of computer aided design (CAD) and computer aided engineering (CAE
Fuzzy scheduling control for gas turbine aero-engine: a multiobjective approach
No full textThis paper investigates the use of a nonconventional approach to control a gas turbine aero-engine. The rationale behind this study is the need to develop advanced tools and techniques that can assist in improving the performance of the system and simultaneously enhance the flexibility of the control strategy. Modern techniques are required for many complex systems where increasingly strict performance and regulatory requirements must be achieved. This is particularly true of aerospace systems where consideration of safety, reliability, maintainability, and environmental impact are all necessary as part of the control requirements. This paper investigates a combination of two such potential techniques: fuzzy logic and evolutionary algorithms. Emerging from new requirements for gas turbine aero-engine control, a flexible gain scheduler is developed and analyzed. A hierarchical multiobjective genetic algorithm is employed to search and optimize the potential solutions for a wide envelope controller covering idle, cruise, and full-power conditions. The overall strategy is demonstrated to be a straightforward and feasible method of refining the control system performance and increasing its flexibility
Developing a control framework for self-adjusting prosthetic sockets incorporating tissue injury risk estimation and generalized predictive control
No full textTo perform activities of daily living (ADL), people with lower limb amputation depend on the prosthetic socket for stability and proprioceptive feedback. Poorly fitting sockets can cause discomfort, pain, limb tissue injuries, limited device usage, and potential rejection. Semi-passively controlled adjustable socket technologies exist, but these depend upon the user’s perception to determine safe interfacial pressure levels. This paper presents a framework for automatic control of an adjustable transtibial prosthetic socket that enables active adaptation of residuum-socket interfacial loading through localized actuators, based on soft tissue injury risk estimation. Using finite element analysis, local interfacial pressure vs. compressive tissue strain relationships were estimated for three discrete anatomical actuator locations, for tissue injury risk assessment within a control structure. Generalized Predictive Control of multiple actuators was implemented to maintain interfacial pressure within estimated safe and functional limits. Controller simulation predicted satisfactory dynamic performance in several scenarios. Actuation rates of 0.06–1.51 kPa/s with 0.67% maximum overshoot, and 0.75–1.58 kPa/s were estimated for continuous walking, and for a demonstrative loading sequence of ADL, respectively. The developed platform could be useful for extending recent efforts in adjustable lower limb prosthetic socket design, particularly for individuals with residuum sensory impairment.</p
A Single-Peak-Structured Solar Cycle Signal in Stratospheric Ozone based on Microwave Limb Sounder Observations and Model Simulations
No full textIndividual file contain TOMCAT CTM simulated ozone profiles from five model simulations analysed in the following publication. Briefly,
vmro3_T2Mz_TOMCAT_A_NRL2_2005-2020.nc contain ozone profiles from the control simulation that uses ERA5 dynamical forcing fields and NRL V2 solar fluxes
vmro3_T2Mz_TOMCAT_B_SATIRE_2005-2020.nc and vmro3_T2Mz_TOMCAT_C_SORCE_2005-2020.nc contain ozone profiles from a simulations that are similar to the control simulation but with SATIRE and SORCE solar fluxes
vmro3_T2Mz_TOMCAT_D_SFix_2005-2020.nc has ozone profiles from simulation that is similar to the control simulation but with fixed solar fluxes, whereas vmro3_T2Mz_TOMCAT_E_DFix_2005-2020.nc also contain ozone profiles from a simulation where model uses annually repeating dynamical fields.
Dhomse, S. S., Chipperfield, M. P., Feng, W., Hossaini, R., Mann, G. W., Santee, M. L., and Weber, M.: A Single-Peak-Structured Solar Cycle Signal in Stratospheric Ozone based on Microwave Limb Sounder Observations and Model Simulations, Atmos. Chem. Phys. Discuss. [preprint], https://doi.org/10.5194/acp-2021-663, in review, 2021
Skeletal muscle microvascular exchange capacity is associated with hyperglycaemia in subjects with central obesity
No full textAims: poor glycaemic control is associated with increased risk of microvascular disease in various organs including the eye and kidney, but the relationship between glycated haemoglobin (HbA1c) and microvascular function in skeletal muscle has not been described. We tested the association between HbA1c and a measure of microvascular exchange capacity (Kf) in skeletal muscle in people with central obesity at risk of developing Type 2 diabetes.Methods: microvascular function was measured in 28 women and 19 men [mean (± sd) age 51 ± 9 years] with central obesity who did not have diabetes. We estimated insulin sensitivity by hyperinsulinaemic–euglycaemic clamp, visceral and total fatness by magnetic resonance imaging, fitness (VO2 max by treadmill testing), physical activity energy expenditure [metabolic equivalents of tasks (METS) by use of the SenseWear Pro armband] and skeletal muscle microvascular exchange capacity (Kf) by venous occlusion plethysmography.Results: in regression modelling, age, sex and fasting plasma glucose accounted for 30.5% of the variance in HbA1c (r2 = 0.31, P = 0.001). Adding Kf to this model explained an additional 26.5% of the variance in HbA1c (r2 = 0.57, P = 0.0001 and Kf was strongly and independently associated with HbA1c (standardized B coefficient ?0.45 (95% confidence interval ?0.19, ?0.06), P = 0.001).Conclusions: we found a strong negative independent association between a measure of skeletal muscle microvascular exchange capacity (Kf) and HbA1c. Kf was associated with almost as much of the variance in HbA1c as fasting plasma glucos
Effects of stratosphere-troposphere chemistry coupling on tropospheric ozone
No full text[1] A new, computationally efficient coupled stratosphere-troposphere chemistry-climate model (S/T-CCM) has been developed based on three well-documented components: a 64-level general circulation model from the UK Met Office Unified Model, the tropospheric chemistry transport model (STOCHEM), and the UMSLIMCAT stratospheric chemistry module. This newly developed S/T-CCM has been evaluated with various observations, and it shows good performance in simulating important chemical species and their interdependence in both the troposphere and stratosphere. The modeled total column ozone agrees well with Total Ozone Mapping Spectrometer observations. Modeled ozone profiles in the upper troposphere and lower stratosphere are significantly improved compared to runs with the stratospheric chemistry and tropospheric chemistry models alone, and they are in good agreement with Michelson Interferometer for Passive Atmospheric Sounding satellite ozone profiles. The observed CO tape recorder is also successfully captured by the new CCM, and ozone-CO correlations are in accordance with Atmospheric Chemistry Experiment observations. However, because of limitations in vertical resolution, intrusion of CO-rich air in the stratosphere from the mesosphere could not be simulated in the current version of S/T-CCM. Additionally, the simulated stratosphere-to-troposphere ozone flux, which controls upper tropospheric OH and O-3 concentrations, is found to be more realistic in the new coupled model compared to STOCHEM.</p
Diastolic function is strongly and independently associated with cardio-respiratory fitness in central obesity
No full textAims/hypothesis: Cardiorespiratory fitness (VO2 max) is an independent risk factor for type 2 diabetes; but in people at risk, factors influencing VO2 max are poorly understood. We tested the hypothesis that VO2 max is associated with diastolic function (SEVR%), (as diastolic function influences myocardial perfusion). Methods: 47 men and women with central obesity without diabetes were studied. We measured fitness (VO2 max) by treadmill testing and diastolic function (SEVR%) by pulse wave analysis. We measured other factors influencing this relationship [insulin sensitivity (M/I) by hyperinsulinemic euglycemic clamp; fatness by MRI and DEXA; physical activity energy expenditure (METS) by Sensewear Pro2; muscle microvascular exchange capacity (Kf) by venous plethysmography]. Results: Mean age [mean (SD) was 51 (9) years]. VO2 max was associated with SEVR% (r=0.50, p=0.001), fatness (r=-0.39, p=0.008) and HbA1c (r=-0.35, p=0.018) but not with M/I, METS or Kf. In regression modelling with age, sex, fatness, and SEVR% as explanatory variables, only age, sex and SEVR% were independently associated with V02 max (SEVR% - standardised B coefficient =0.37 ((95%CIs 0.003, 0.18), p=0.007). 46% of the variance in VO2 max (r2=0.46 p=0.0001) was identified by this model. Conclusions/interpretation: There was a strong, independent association between VO2 max and a measure of diastolic function in sedentary people with central obesity
Engineering beta cell mass regulation in diabetes
No full text?-cell failure, encompassing a range of aberrant cellular processes from dysfunction to death, has long been recognised as the central defect in Type 1 Diabetes Mellitus (T1DM), but is now also accepted as a major factor in essentially all other types of diabetes, notably the “epidemic” variant, Type 2 Diabetes (T2DM). However, the mechanisms involved differ as exemplified by prominent role ascribed to the immune system and extrinsic pathway of apoptosis in T1DM and to metabolic insults (gluco- and lipo- toxicity) in T2DM. Intriguingly, common ground is emerging, whereby ?-cell renewal, death and plasticity are influenced by combinations of environmental factors, including metabolic changes, immune processes, cell-cell contacts and growth factors acting on ?-cells rendered either resistant or prone to cell death by intracellular signaling pathways, such as the IRS2/PI3K/AKT/mTOR pathway and master regulatory proteins such as c-Myc. Moreover, maintaining a functional ?-cell mass does not merely require avoiding destruction and dysfunction, but also renewal by self-replication and/or differentiation from precursors. Finally, the fact that processes regulating growth and death are intimately linked and also impact on function creates intriguing conundrums- for instance is there a maximum number/proportion of ?-cells that can be replicating at any one time without compromising ability to control blood glucose. This is very pertinent as rising glucose could accelerate ?-cell losses and or further compromise renewal thus constituting a spiral to catastrophe and transition from compensated insulin resistance to overt diabetes. Important new therapies are exploiting knowledge of beta cell mass regulation and function and further advances may finally unleash the potential of ?-cell targeted treatments and even cell-based therapies for diabetes. This exciting area will be the focus of this review
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