Antarctic ozone recovery

Since 1976, and more so since 1985, the Antarctic ozone level has suffered considerable depletion (termed as Antarctic ozone hole), attributed to the destructive effects of CFC compounds leaking into the atmosphere from man-made gadgets. The 12-month running means of South Pole Dobson ozone (monthly means, upto 1999 end only) were subjected to spectral analysis, which showed considerable, significant amplitudes for QBO (Quasi-biennial, 2-3 years) and QTO (Quasi-triennial, 3-4 years) oscillations, with a total range of 20-30 DU. When subtracted from the original values, a fairly smooth variation was seen, with a decrease from ~260 DU in 1986 to ~230 DU in 1996 (~12% decrease in 12-month running means), and an almost steady level thereafter. Thus, the net ozone variation at South Pole consists of two parts, (i) a long-term monotonically downward trend upto 1996 and a steady level thereafter and (ii) a superposed QBO-QTO oscillation. The chemical destruction effect is not likely to disappear soon, and may even increase if greenhouse effects, major volcanic eruptions or enhanced stratospheric cooling intervene. If the long-term level (i) remains steady, an extrapolation of the QBO-QTO patterns indicates that the ozone level is due for an increase from about 1999 end to about 2001 beginning. The purpose of the present analysis is to point out that, if such an increase of 20-30 DU occurs, it should not be misinterpreted as due to a decrease in chemical destruction, which scientists are eagerly awaiting due to the indication of a reduction in the halogen load in recent years due to adherence to the Montreal Protocol. After one or two years (in 2002), the extrapolated QBO-QTO oscillation may bring down the ozone level back again to the 1999 end level, and the apparent recovery may turn out to be a false signal.

Humans optimally anticipate and compensate for an uneven step during walking

The simple task of walking up a sidewalk curb is actually a dynamic prediction task. The curb is a disturbance that could cause a loss of momentum if not anticipated and compensated for. It might be possible to adjust momentum sufficiently to ensure undisturbed time of arrival, but there are infinite possible ways to do so. Much of steady, level gait is determined by energy economy, which should be at least as important with terrain disturbances. It is, however, unknown whether economy also governs walking up a curb, and whether anticipation helps. Here we show that humans compensate with an anticipatory pattern of forward speed adjustments, predicted by a criterion of minimizing mechanical energy input. The strategy is mechanistically predicted by optimal control for a simple model of bipedal walking dynamics, with each leg's push-off work as input. Optimization predicts a tri-phasic trajectory of speed (and thus momentum) adjustments, including an anticipatory phase. In experiment, human subjects ascend an artificial curb with the predicted tri-phasic trajectory, which approximately conserves overall walking speed relative to undisturbed flat ground. The trajectory involves speeding up in a few steps before the curb, losing considerable momentum from ascending it, and then regaining speed in a few steps thereafter. Descending the curb entails a nearly opposite, but still anticipatory, speed fluctuation trajectory, in agreement with model predictions that speed fluctuation amplitudes should scale linearly with curb height. The fluctuation amplitudes also decrease slightly with faster average speeds, also as predicted by model. Humans can reason about the dynamics of walking to plan anticipatory and economical control, even with a sidewalk curb in the way.

UH-60A Airloads Workshop—Setting the Stage for the Rotorcraft CFD/CSD Revolution, Part I: Background and Initial Success

The UH-60A Airloads Workshop was a unique collaboration of aeromechanics experts from the U.S. Government, industry, and academia to address technical issues that hindered accurate rotor loads predictions. The Airloads Workshop leveraged the NASA/Army UH-60A Airloads flight test and NFAC wind tunnel test data. It functioned continuously for 17 years, from 2001 to 2018, and brought about one of the most important advancements in rotorcraft aeromechanics prediction capabilities by successfully demonstrating high-fidelity coupled computational fluid dynamics (CFD) and computational structural dynamics (CSD) analyses for both steady and maneuvering flight. The article is divided into two parts. Part I surveys the background of rotorcraft CFD/CSD development difficulties, the origins of the Airloads Workshop, and the rapid success achieved during the first phase that consisted of eight Workshops. Part II describes ongoing development during the subsequent two phases of the Airloads Workshop, the Ninth through the 13th, and the 14th through the 31st Workshops; the impact of the Airloads Workshop; and the lessons learned. Part I surveys the technical activities that led to a breakthrough for CFD/CSD coupling to successfully predict rotor blade airloads in trimmed steady-level flight conditions. This success illustrated the importance of collaboration among key experts with diverse backgrounds focused on a common objective to advance rotorcraft prediction methods.

Variations in oxidative stress and antioxidant defense level during different phases of hibernation in common Asian toad, Duttaphrynus melanostictus

To assess redox status during hibernation with metabolic depression, oxidative stress parameters and antioxidant defense were assessed during different phases of hibernation including active period, hibernation, arousal, and post arousal period, in the liver and brain tissues of Duttaphrynus melanostictus. We hypothesized low levels of oxidative stress and antioxidant defense during the hibernation period in comparison to the summer active period due to hypometabolism and their subsequent increase during the arousal period following an increase in body temperature and metabolism. Contrary to our hypothesis increased oxidative stress with significantly higher lipid peroxidation, protein carbonylation, GSSG/GSH ratio, and elevated antioxidants defense consisting of higher catalase activity and high ascorbic acid content to control oxidative stress were found during hibernation. However, GSH and uric acid levels were found low with SOD activities at a steady level during hibernation. Supporting our hypothesis increased oxidative stress with high lipid peroxidation and GSSG/GSH ratio were found during arousal from hibernation owing to increased oxygen consumption and rewarming. Augmented catalase and SOD activities and nonenzymatic antioxidants (GSH, ascorbic acid, and uric acid) level were found to counteract oxidative stress during arousal periods as it was expected. A steady level of protein carbonylation indicating no oxidative damage during arousal from hibernation due to elevated antioxidant defense shows the significance of hibernation to overcome food and water scarcity and cold climatic condition. Decrease in antioxidants levels accompanying coming down of lipid peroxidation, protein carbonylation, and GSSG/GSH ratio to their lower levels during post arousal period showing normalcy in redox status as it was during active period indicates controllability of oxidative stress in hibernating toads.

Trim Solutions of Multirotor Vehicles using a Fast Performance Prediction Method

A fast multirotor performance prediction method is presented. The method uses an algorithm to determine the flight performance and trim solutions of multirotor vehicles in steady, level flight. The method considers parasitic drag, force trim, fuselage interference, rotor interference, moment trim, and power prediction. In order to validate the method, vehicle lift, drag, and pitching moment predictions are compared to experimental data from NASA Ames for the 3DR Solo, a commercially available vehicle. The performance comparison with wind tunnel data show similar lift, drag and pitching moment trends when using estimated rotor and vehicle geometries. In addition, the predicted rotor speeds, vehicle power, and vehicle pitch are compared to flight test data of the Aeryon SkyRanger. The lead and rear rotor speed results show that the application of moment trim into the performance model provides rotor speed estimates that reflect the differential rotor speeds the flight test. An orientation study is conducted to explore the effects of rotor and fuselage interference velocities on rotor performance and the performance differences of a four-rotor vehicle flying in diamond and square configurations. Finally, a mass offset study is presented to predict the changes in rotor speed distribution of a SkyRanger vehicle when a 100 g mass is added to the support arm, which simulates asymmetry in centre of gravity location. The predicted performance results show overlapping results with flight testing with and without the mass offset at airspeeds below 5 m/s. At higher airspeeds, the rotor speed predictions that are established by moment trim requirements reflect the rotor speed trends shown from flight test data.

Trim Solutions of Multirotor Vehicles using a Fast Performance Prediction Method

A fast multirotor performance prediction method is presented. The method uses an algorithm to determine the flight performance and trim solutions of multirotor vehicles in steady, level flight. The method considers parasitic drag, force trim, fuselage interference, rotor interference, moment trim, and power prediction. In order to validate the method, vehicle lift, drag, and pitching moment predictions are compared to experimental data from NASA Ames for the 3DR Solo, a commercially available vehicle. The performance comparison with wind tunnel data show similar lift, drag and pitching moment trends when using estimated rotor and vehicle geometries. In addition, the predicted rotor speeds, vehicle power, and vehicle pitch are compared to flight test data of the Aeryon SkyRanger. The lead and rear rotor speed results show that the application of moment trim into the performance model provides rotor speed estimates that reflect the differential rotor speeds the flight test. An orientation study is conducted to explore the effects of rotor and fuselage interference velocities on rotor performance and the performance differences of a four-rotor vehicle flying in diamond and square configurations. Finally, a mass offset study is presented to predict the changes in rotor speed distribution of a SkyRanger vehicle when a 100 g mass is added to the support arm, which simulates asymmetry in centre of gravity location. The predicted performance results show overlapping results with flight testing with and without the mass offset at airspeeds below 5 m/s. At higher airspeeds, the rotor speed predictions that are established by moment trim requirements reflect the rotor speed trends shown from flight test data.

Development of a Flexible Framework Multi-Design Optimization Scheme for a Hand Launched Fuel Cell-Powered UAV

This paper presents different methods for the design of a hand-launchable, fixed wing, fuel cell-powered unmanned aerial vehicle (UAV) to maximize flight endurance during steady level flight missions. The proposed design methods include the development of physical models for different propulsion system components. The performance characteristics of the aircraft are modeled through empirical contributing analyses in which each analysis corresponds to an aircraft subsystem. The contributing analyses are collected to form a design structure matrix which is included into a multi-disciplinary analysis to solve for the design variables over a defined design space. The optimal solution is found using a comprehensive optimization tool developed for long endurance flight missions. Optimization results showed a significant improvement in UAV flight endurance that reached up to 475 min with take-off ratio equals to 59 min/kg. Wind tunnel and bench-top tests and HiL simulation tests are performed to validate the results obtained from the optimization tools. Validated optimization results showed an increase of the overall UAV flight endurance by 19.4% compared to classical approaches in design methods.

Assessment of a Mid-Fidelity Numerical Approach for the Investigation of Tiltrotor Aerodynamics

The study of the complex aerodynamics that characterise tiltrotors represents a challenge for computational fluid dynamics tools. URANS numerical solvers are typically used to explore the aerodynamic features that characterise the different flight conditions of these aircraft, but their computational cost limits their applications to a few vehicle configurations. The present work explores the capabilities of a new mid-fidelity aerodynamic code that is based on the vortex particle method, DUST, to investigate the performance and flow physics of tiltrotors. With this aim, numerical simulations were performed in DUST while considering XV-15 tiltrotor configurations with increasing complexity. The study started with the investigation of a simpler configuration made up of a single wing and a proprotor. Subsequently, the full aircraft was studied in steady-level flights and its major operating flight conditions were explored—i.e., hover, conversion phase, and cruise. A thorough assessment of the code capabilities was performed by the comparison of the numerical results with high-fidelity Computational Fluid Dynamics (CFD) data. This thorough comparison showed that the mid-fidelity numerical approach implemented in DUST is suitable for capturing the flow physics related to the complex aerodynamic interactions between the proprotors and the wing along with the entire flight envelope of the tiltrotor. Moreover, a good representation of the aerodynamic performance of the vehicle was obtained, particularly for the flight conditions that are characterised by limited flow separations. The good accuracy obtained for both the performance and flow physics, combined with the relatively lower computational costs required by the mid-fidelity solver with respect to the URANS simulations, indicates that DUST could be considered a valuable tool for use in the preliminary design of novel tiltrotor configurations.

Optimal Segment Control of Active Twist Rotor for Power Reduction in Forward Flight

The segment control of active twist rotor is investigated to evaluate the effectiveness in rotor power reduction. A numerical model for predicting the isolated rotor power and loads in steady level flights is deployed and validated. A parametric sweep of the amplitude and phase angle for uniform single-harmonic active twist control is conducted to demonstrate the mechanism of active twist control in rotor power reduction. The optimal control schedules and segment layouts of the segment twist control for power reduction while considering saturation limits are obtained using an optimization framework based on genetic algorithm. Up to 5-seg configuration is considered. The results indicate that the segment twist control reduces the rotor power more than the uniform twist control by applying divergent control schedules to each segment. The load distribution of the rotor disk is harmonized in both circumferential and spanwise directions. The 2-seg and 3-seg control configurations are appropriate, while the configurations with more segments yield limited benefits and they may be penalized with an increase in system complexity.

Maintaining Optimum Health Requires Longer-Term Stable Vitamin D Concentrations

Humans are constantly invaded by environmental microbes. The body is protected from pathogen attacks by the immune defense system. In 99.8% of the time, our innate immune system is capable of getting rid of these organisms without before these can cause harm. Those who are with weaker immune systems constantly get infections and having chronic diseases. Among many factors contributing to maintaining a robust immune system, vitamin D has the highest impact. It has a major protective effect against acute respiratory infections and subduing both communicable and non-communicable diseases. A healthy person with stronger immunity may not manifest clinical signs and symptoms of COVID-19-silent, asymptomatic carriers of the virus and can be infectious. Whereas not all PCR positive persons are infectious. A rapid response occurs through the innate system that is followed by the adaptive response that lasts a longer period. Vitamin D kick starts both systems. However, the protective immune and other functions are damped in the presence of hypovitaminosis and also when the levels are fluctuating. Thus, the importance of maintaining serum 25(OH)D at a steady level above 30 ng/mL. When maintaining such, among all nutrients vitamin D has the widest benefits to multiple body systems. Thus, this sunshine vitamin (a steroid hormone) has been modulated through evolution to emerge as a key survival mechanism in humans. Nevertheless, vitamin D is not a panacea.