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Kinetics of force-mediated chemical reactions of end-tethered polymers with varying chain length N in varying shear rate flow γ ̇ are explored via coarse-grained Brownian dynamics simulations. At fixed γ ̇ , force F along a polymer increases linearly with N as previously predicted; however, contrary to existing theory, the F(N) slope increases for N above a transition length that exhibits minimal dependence on γ ̇ . Force profiles are used in a stochastic model of a force-mediated reaction to compute the time for x percent of a polymer population to experience a reaction, tx. Observations are insensitive to the selected value of x in that tx data for varying N and γ ̇ can be consistently collapsed onto a single curve via appropriate scaling, with one master curve for systems below the transition N (small N) and another for those above (large N). Different force scaling for small and large N results in orders of magnitude difference in force-mediated reaction kinetics as represented by the population response time. Data presented illustrate the possibility of designing mechano-reactive polymer populations with highly controlled response to flow across a range in γ ̇ . [ABSTRACT FROM AUTHOR]

In this study, we address the trajectory tracking control problem for stratospheric airships, characterized by parameter uncertainties and external disturbances. Initially, a mathematical model of the airship is constructed, from which a trajectory tracking error model is derived. Subsequently, a novel sliding mode control law is formulated to enhance control accuracy and accelerate the convergence rate of the sliding mode. Furthermore, radial basis function neural networks are utilized to estimate and compensate for uncertain system parameters and external disturbances, significantly improving the system's robustness. Lastly, the application of Lyapunov's theory verifies the fixed-time stability of the closed-loop system and ensures the convergence of trajectory tracking error to a near-zero vicinity within fixed time. Simulation results strongly support the efficacy of the proposed control strategy. [ABSTRACT FROM AUTHOR]

This paper presents a guidance and control system for controlling the trajectory of a stratospheric unmanned airship using a cascaded Incremental Nonlinear Dynamic Inversion (INDI) method. The control system uses a two-loop cascaded INDI controller with virtual efforts and moments formulation to control both the airship attitude and velocity, while providing perturbation rejection properties. An active-set solver allocates the virtual controls to the airship propellers and aerodynamic surfaces while respecting the actuator bounds and rates saturation. The guidance system uses a Nonlinear Dynamic Inversion controller, where the position error dynamics formulation explicitly considers the lateral velocity of the airship, which enables it to counteract the wind influence. Simulation results demonstrate that the reference trajectory is precisely followed, even in the presence of unknown wind perturbations and both aerodynamic coefficients and mass and inertia parametric uncertainties through Monte-Carlo simulations. [ABSTRACT FROM AUTHOR]

In this paper, the path-following problem for an underactuated stratospheric airship with unknown dynamics and external disturbances has been studied. Vector field guidance is employed to fix the underactuated issue and generate desired heading. Time-delay control (TDC) is utilised to track desired states and estimate the model uncertain and disturbances using simple delayed states. To compensate time-delay estimation (TDE) errors, terminal sliding-mode is utilised and combined with TDC. The stability of the proposed controller is provided by using Lyapunov function. A numerical simulation is demonstrated to prove the performance of the proposed control algorithm. [ABSTRACT FROM AUTHOR]

The stratospheric airship, as a near-space vehicle, is increasingly utilized in scientific exploration and Earth observation due to its long endurance and regional observation capabilities. However, due to the complex characteristics of the stratospheric wind field environment, trajectory planning for stratospheric airships is a significant challenge. Unlike lower atmospheric levels, the stratosphere presents a wind field characterized by significant variability in wind speed and direction, which can drastically affect the stability of the airship's trajectory. Recent advances in deep reinforcement learning (DRL) have presented promising avenues for trajectory planning. DRL algorithms have demonstrated the ability to learn complex control strategies autonomously by interacting with the environment. In particular, the proximal policy optimization (PPO) algorithm has shown effectiveness in continuous control tasks and is well suited to the non-linear, high-dimensional problem of trajectory planning in dynamic environments. This paper proposes a trajectory planning method for stratospheric airships based on the PPO algorithm. The primary contributions of this paper include establishing a continuous action space model for stratospheric airship motion; enabling more precise control and adjustments across a broader range of actions; integrating time-varying wind field data into the reinforcement learning environment; enhancing the policy network's adaptability and generalization to various environmental conditions; and enabling the algorithm to automatically adjust and optimize flight paths in real time using wind speed information, reducing the need for human intervention. Experimental results show that, within its wind resistance capability, the airship can achieve long-duration regional station-keeping, with a maximum station-keeping time ratio (STR) of up to 0.997. [ABSTRACT FROM AUTHOR]

In response to the problem of disturbance in the imaging equipment of stratospheric airships, this study designs a vibration isolation and stability system for carrying imaging equipment. The system mainly consists of microprocessor, gimbal, voice coil motor (VCM) and rubber ring. By using adaptive control law based on characteristic model to control the double closed control loop of the motor composed of position loop and speed loop, the camera deflection caused by disturbance is effectively eliminated. Furthermore, in vertical vibration suppression, the adaptive control law based on the characteristic model is also applied to the double closed control loop of the voice coil motor, which removes most of the vertical vibration and realizes active vibration isolation. The passive isolation of the system is completed by rubber rings. The experimental results show that the vibration isolation and stabilization system have good performance in complex disturbance environments, effectively stabilizing the imaging equipment. [ABSTRACT FROM AUTHOR]

The exacerbation of air pollution during spring in Yunnan province, China, has attracted widespread attention. However, many studies have focused solely on the impacts of anthropogenic emissions while ignoring the role of natural processes. This study used satellite data spanning 21 years from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Atmospheric Infrared Sounder (AIRS) to reveal two natural processes closely related to springtime ozone (O3) and PM2.5 pollution: stratospheric intrusions (SIs) and cross-border transport of biomass burning (BB). We aimed to assess the mechanisms through which SIs and cross-border BB transport influence O3 and PM2.5 pollution in Southwestern China during the spring. The unique geographical conditions and prevalent southwest winds are considered the key driving factors for SIs and cross-border BB transport. Frequent tropopause folding provides favorable dynamic conditions for SIs in the upper troposphere. In the lower troposphere, the distribution patterns of O3 and stratospheric O3 tracer (O3S) are similar to the terrain, indicating that O3 is more likely to reach the surface with increasing altitude. Using stratospheric tracer tagging methods, we quantified the contributions of SIs to surface O3, ranging from 6 to 31 ppbv and accounting for 10–38% of surface O3 levels. Additionally, as Yunnan is located downwind of Myanmar and has complex terrain, it provides favorable conditions for PM2.5 and O3 generation from cross-border BB transport. The decreasing terrain distribution from north to south in Yunnan facilitates PM2.5 transport to lower-elevation border cities, whereas higher-elevation cities hinder PM2.5 transport, leading to spatial heterogeneity in PM2.5. This study provides scientific support for elucidating the two key processes governing springtime PM2.5 and O3 pollution in Yunnan, SIs and cross-border BB transport, and can assist policymakers in formulating optimal emission reduction strategies. [ABSTRACT FROM AUTHOR]

When it comes to computing the values of variables defining the preliminary sizing of an airship, a few standardized approaches are available in the existing literature. However, when including a disruptive technology in the design is required, sizing procedures need to be amended, so as to be able to deal with the features of any additional novel item. This is the case of atmospheric ionic thrusters, a promising propulsive technology based on electric power, where thrusters feature no moving parts and are relatively cheap to manufacture. The present contribution proposes modifications to an existing airship design technique, originally conceived accounting for standard electro-mechanical thrusters, so as to cope with the specific features of new atmospheric ionic thrusters. After introducing this design procedure in detail, its potential is tested by showing results from feasibility studies on an example airship intended for a high-altitude mission. Concurrently, the so-obtained results allow the demonstration of the sizing features corresponding to the adoption of atmospheric ionic thrusters at the current level of technology, comparing them to what is obtained for the same mission when employing a standard electro-mechanical propulsion system. [ABSTRACT FROM AUTHOR]

A fast trajectory tracking controller is designed for the airship, involving dynamic uncertainties of parameters, capable of guaranteeing the prescribed performance of tracking errors, and fast response of the closed-loop system. To achieve the decoupling of velocity control and attitude control of the airship, a new guidance and control integration framework is proposed first. Then, based on the dynamics model established by the spinor method, the lumped disturbance, caused by unknown aerodynamic parameter uncertainties and exogenous disturbances, is estimated online using a high-order finite-time observer. The control performance, namely, overshoot and steady-state performance of tracking errors, is significantly improved by utilizing the prescribed output performance constraints, while the convergence rate is further enhanced by combining the finite-time convergence property of the fast terminal sliding mode control. Simulation results attest to the effectiveness of the strategy in this paper. Compared with the adaptive fast terminal sliding mode control, the strategy effectively utilizes the capability of the actuator within the allowed range and reduces the convergence time by more than half with similar control inputs. [ABSTRACT FROM AUTHOR]

Situated at a land-sea interface, Houston, Texas, is a national hub for the petrochemical industry and has the second fastest-growing metropolitan population in the United States. Addressing air quality in this region is uniquely challenging, due in part to its wide range of meteorological conditions (e.g. , convection systems and temperature inversions) and continuum of volatile organic compound (VOC) and aerosol sources (e.g. , anthropogenic and biogenic). As a result, Houston was chosen as the location for the Department of Energy's Atmospheric Radiation Measurement (ARM) program-led Tracking Aerosol Convection ExpeRiment (TRACER), which investigated cloud and aerosol interactions in the deep convection over the area. Deployed as a key asset, ARM's tethered balloon system (TBS) was used to investigate questions related to the vertical distributions of aerosols and their formation, including their precursor species volatile organic compounds. Platforms like TBSs and uncrewed aerial vehicles (UAVs) can bridge the vertical gap between ground-based and crewed airplane measurement platforms to focus on near-surface characterization. However, there has been limited effort to modularize and integrate VOC samplers into instrument payloads on both aerial systems. In this study, lightweight and robust VOC samplers were designed and deployed on the TBS and a UAV to collect VOCs in flight. The modular design allowed for scalable adjustments to meet the unique platform requirements and enabled multiple flights per sampling day. Each sampler can autonomously collect VOCs on up to four sorbent tubes for subsequent thermal desorption-gas chromatography-mass spectrometry analysis. The low sampler mass (2.2 kg and 800 g, TBS and UAV, respectively) enables the combination of these VOC samplers with trace gas, aerosol, and meteorological sensors on aerial platforms. These profiles allow us to assess temporal changes in VOC magnitude and composition at multiple locations. Observations from TBS and UAV flights during TRACER are presented and future considerations for sampler design and deployments are discussed. [ABSTRACT FROM AUTHOR]

The text investigates a specific aspect of dreams and dreaming, which is best described with reference to the Freudian concept of 'the Uncanny'. By combining psychoanalytical knowledge with concepts developed within the frame of empirical dream research, the dream generation model by Moser and v. Zeppelin is applied in order to discuss aspects of Dream-work. Dream-processes are described as oscillating between two areas – a familiar and an unfamiliar world. The approach to unfamiliar material in a dream implies the potential of uncanniness. Thus, every dream contains potentially uncanny material. Clinical implications for dream interpretations are discussed. [ABSTRACT FROM AUTHOR]

This study proposes a numerical model to simulate the thermal characteristics of stratospheric airships (SA). This model introduces a simple yet accurate method for the selection of the optical bands for target detection based on multispectral features. The key to this model is the selection of the spectral bands in which a significant radiation difference exists between the target and its surrounding background. Using the signal-to-noise ratio (SNR), detection probability, and false alarm rate as model evaluation metrics, and based on the analysis of the radiation differences between the target and atmospheric background, it is found that there are two narrow bands possible for SA detection: one with a central wavelength of 8.83 µm and a bandwidth of 0.35 µm and the other with a central wavelength of 11.51 µm and a bandwidth of 0.34 µm. Further numerical simulations and theoretical analyses under varying space environments demonstrate that considerable detection potential can be achieved; thus, the presented optical detection model is useful for the night detection of SA targets. [ABSTRACT FROM AUTHOR]

Overshooting tops (OTs) are manifestations of deep convective updrafts that extend above the tropopause into the stratosphere. They can induce dynamic perturbations and result in irreversible transport of aerosols, water vapor and other mass from the troposphere into the stratosphere, thereby impacting the chemical composition and radiative processes of the stratosphere. These and other effects of OTs depend on their characteristics such as depth and area, which are understood to connect to mid‐tropospheric updraft speed and width, respectively. Less understood is how static stability in the lower stratosphere (LS) potentially modulates these OT–updraft connections, thus motivating the current study. Here, LS static stability and observed OT characteristics are quantified and compared using a combination of reanalysis data, observed rawinsonde data and geostationary satellite data. A weak to moderate relationship between OT depth and LS lapse rate and Brunt‐Väisälä frequency (N2) (R = 0.38, −0.37, respectively) is found, implying that OT depth is reduced with an increasingly stable LS. In contrast, a weak relationship (R = −0.03, 0.03, respectively) is found between OT area and LS static stability, implying that OT area is controlled primarily by mid to upper tropospheric updraft area. OT duration has a weak relationship to LS lapse rate and N2 (R = 0.02, −0.02, respectively). These relationships may be useful in interpreting mid‐ and low‐level storm dynamics from satellite‐observed characteristics of OTs in near real‐time. Plain Language Summary: An overshooting top (OT) is a domed protrusion of a storm that reaches the stratosphere. These phenomena are important for their impact on stratospheric chemistry and their relationship to on‐the‐ground severe weather hazards. Spatial trends in OTs in southeastern South America are explored. Additionally, it is shown that static stability in the LS can be related to some aspects of OTs. Key Points: Overshooting tops (OTs) with the largest area occur across the study domain while OTs with the largest depth occur largely in one clusterOvershooting top area is weakly related to lower stratosphere (LS) static stabilityOvershooting top depth is weakly to moderately related to LS static stability [ABSTRACT FROM AUTHOR]

Stratospheric airships require a lightweight envelope to contain lighter-than-air buoyancy gas, making the lightweight design and pressure-bearing performance of the envelope structure a key research issue. The stress state at different cross-sectional positions of the airship envelope structure is different, resulting in a low utilization rate of the overall material performance of the envelope structure. This paper proposes a design scheme for reinforcing envelope structures with sliding reinforcing cable to improve the bearing capacity of the composite fabric structure while reducing its weight, ultimately achieving the optimal strength-to-weight ratio. Two types of composite fabric structures (A-airship and B-airship) were subjected to inflatable burst tests, and the strain changes in the envelope gores were analyzed by digital image correlation. Through re-assembly of the broken composite fabric pieces and analysis of their tear textures, crack origination positions, failure causes, and the stress behavior and state at the failure position were identified. An envelope structural model with consideration of the cutting pattern effect was established, allowing the stress distribution of the envelope to be analyzed and the damage positions to be more accurately predicted. Based on the analysis of the ultimate pressure-bearing performance of an airship envelope structure, a novel idea of incorporating coupled tensile-shear stress into the strength criterion was proposed. Through the data in the study and existing references, it is verified that the strength criterion can accurately predict the ultimate pressure-bearing performance of the envelope structure. [ABSTRACT FROM AUTHOR]

In this paper, we applied a variety of statistical methods to study gravity waves in the troposphere and lower stratosphere in the Brazilian sector, using a large database from Instituto de Controle do Espaço Aéreo (ICEA) of radiosonde measurements carried out in 2014 at 32 locations in the Brazilian territory totaling 49,652 wind and temperature profiles. The average wind profiles were computed and classified by means of a hierarchical cluster analysis. The kinetic and potential energy densities of gravity waves were determined using a detrending technique based on the Least Squares Method and the Fast Fourier Transform. By analyzing the energy density time series it was found that tropospheric average values are consistently larger in the months of winter, late autumn and early spring. Stratospheric average values of variability and kinetic energy density are also consistently larger in this period. A systematic search for quasi monochromatic waves was carried out and their main characteristics such as horizontal/vertical wavelengths and velocities were determined both in the troposphere and lower stratosphere. A correlation analysis between the troposphere and the lower stratosphere based on the measured parameters was used to investigate the wave coupling between the two layers, and no significant correlation was found. Finally, a spatial correlation analysis between energy densities measured at different aerodromes in the same atmospheric layer was carried out, showing that energy densities are spatially correlated for distances less than 3,000–4,000 km. Plain Language Summary: Like waves in the ocean that can be easily seen by any observer in the beach, the atmosphere is also permeated by waves of similar nature, called Gravity Waves (GWs). These waves transport energy through the atmosphere, eventually breaking, reflecting or dissipating at some point. In this work we investigated the characteristics of these waves using weather data retrieved by weather balloons released from several locations in the Brazilian territory in 2014. By analyzing the measurements, we quantified parameters related to GWs, such as the kinetic and potential energy densities. We also investigated GWs that have well defined frequencies, called monochromatic waves, and determined their wavelengths, phases, amplitudes and phase velocities. We did not find correlations between the wave energies in the troposphere and the low stratosphere, which is an evidence of weak coupling between both layers. This result suggests that GWs characteristics are substantially modified in the perturbed, turbulent and windy region between the troposphere and low stratosphere. Moreover, we also identified the prevailing behavior of the winds in each of the studied locations. Key Points: A comprehensive survey on gravity waves using radiosonde data from 32 locations in the Brazilian territory totaling 49,652 profilesThe energy densities of gravity waves are spatially correlated within a region of approximately 3,000 km of radiusIt was found that gravity waves propagating in the troposphere and low stratosphere are uncorrelated in the studied locations [ABSTRACT FROM AUTHOR]

Heliotropes are passive solar hot-air balloons that are capable of achieving nearly level flight within the lower stratosphere for several hours. These inexpensive flight platforms enable stratospheric sensing with high cadence enabled by the low cost to manufacture, but their performance has not yet been assessed systematically. During July–September of 2021, 29 heliotropes were successfully launched from Oklahoma and achieved float altitude as part of the Balloon-based Acoustic Seismology Study (BASS). All of the heliotrope envelopes were nearly identical with only minor variations to the flight line throughout the campaign. Flight data collected during this campaign comprise a large sample to characterize the typical heliotrope flight behavior during launch, ascent, float, and descent. Each flight stage is characterized, dependence on various parameters is quantified, and a discussion of nominal and anomalous flights is provided. [ABSTRACT FROM AUTHOR]

Building on previous linguistic evaluations of media awards the present study uses integrative complexity (IC)—a rhetorical construct and psycholinguistic variable—to explore Nickelodeon's Kids' Choice Awards (KCAs), comparing the dialogue from the winners and nominees. The KCAs represent a unique opportunity for study because (a) although not viewed as prestigious as other awards (e.g., the Academy Awards or Golden Globes), they occupy an established space of cultural relevance, and (b) unlike most media awards, they prioritize kids, who form the voter base. Focusing specifically on the film categories, statistical analysis found significant negative relationships between IC and winning. These results reflect the findings from previous research, indicating that IC meaningfully predicts outcomes for media awards and that a shared psychology in terms of linguistic perception and how it relates to winning media awards may exist. In conjunction with previous research, the present study's results overall suggest that IC has a place within predictive models used to assess and evaluate entertainment media. [ABSTRACT FROM AUTHOR]

Observational monitoring of the stratospheric transport circulation, the Brewer–Dobson circulation (BDC), is crucial to estimate any decadal to long-term changes therein, a prerequisite to interpret trends in stratospheric composition and to constrain the consequential impacts on climate. The transport time along the BDC (i.e. the mean stratospheric age of air, AoA) can best be deduced from trace gas measurements of tracers which increase linearly with time and are chemically passive. The gas sulfur hexafluoride (SF 6) is often used to deduce AoA because it has been increasing monotonically since the ∼ 1950s, and previously its chemical sinks in the mesosphere have been assumed to be negligible for AoA estimates. However, recent studies have shown that the chemical sinks of SF 6 are stronger than assumed and become increasingly relevant with rising SF 6 concentrations. To adjust biases in AoA that result from the chemical SF 6 sinks, we here propose a simple correction scheme for SF 6 -based AoA estimates accounting for the time-dependent effects of chemical sinks. The correction scheme is based on theoretical considerations with idealized assumptions, resulting in a relation between ideal AoA and apparent AoA which is a function of the tropospheric reference time series of SF 6 and of the AoA-dependent effective lifetime of SF 6. The correction method is thoroughly tested within a self-consistent data set from a climate model that includes explicit calculation of chemical SF 6 sinks. It is shown within the model that the correction successfully reduces biases in SF 6 -based AoA to less than 5 % for mean ages below 5 years. Tests using only subsampled data for deriving the fit coefficients show that applying the correction scheme even with imperfect knowledge of the sink is far superior to not applying a sink correction. Furthermore, we show that based on currently available measurements, we are not able to constrain the fit parameters of the correction scheme based on observational data alone. However, the model-based correction curve lies within the observational uncertainty, and we thus recommend using the model-derived fit coefficients until more high-quality measurements are able to further constrain the correction scheme. The application of the correction scheme to AoA from satellites and in situ data suggests that it is highly beneficial to reconcile different observational estimates of mean AoA. [ABSTRACT FROM AUTHOR]

This paper proposes a new kind of airship actuator configuration for surveillance and environmental monitoring missions. We present the design and application of a six-propeller electrical airship (Noamini) with independent tilting propellers, allowing improved and flexible maneuverability. The vehicle has different combinations of differential propulsion and can be used in a two-, four- or six-motor configuration. We developed a high-fidelity airship simulator for the Noamini airship, which was used to test and validate a control/guidance approach. Incremental Nonlinear Dynamic Inversion (INDI) is used for the velocity/attitude control to follow a high-level L1 guidance reference in a simulated waypoint-tracking mission with wind and turbulence. The proposed framework will be soon implemented in the onboard control system of the Noamini, an autonomous airship for environmental monitoring and surveillance applications. [ABSTRACT FROM AUTHOR]

Hybrid airships, combining aerodynamic lift and buoyant lift, are efficient near-space aircraft for scientific exploration, observation, and surveillance. Compared to conventional airplanes and airships, hybrid airships offer unique advantages, including stationary hovering and rapid deployment. Due to the different task requirements and strong coupling between flight and environment, trajectory-optimization methods for traditional aircraft are difficult to apply to hybrid airships directly. We propose a trajectory-optimization model based on the variational method to calculate the optimal time and energy paths under weak, uniform, and latitudinal linear wind fields. Our model shows that the influencing factors for the optimization path can be categorized into three types: airship design parameters, wind field parameters, and departure parameters. The result indicates that the optimal time paths are generally straight lines, and the optimal energy paths are piecewise curves with a 24-h cycle under typical hybrid airship design parameters. This work has provided new insight into the trajectory optimization and parameter design of future hybrid airships. [ABSTRACT FROM AUTHOR]

With the growing demand of low-cost transportation service, Hybrid airship plays a significant role for providing this service as a cargo nowadays. This paper deals with the controller design for winged hybrid airship with suspended payload for maintaining stability and controllability of the system. Controller design is required for the system to achieve desired tracking performance and collision avoidance for closed loop analysis. Internal Model Control (IMC) compensator is also designed to make few subsystems represented as velocity transfer function stable. The system is a small sized winged hybrid airship with attached suspended payload and having controlling maneuvers like elevator. The system taken is discussed as an approach of single body longitudinal dynamics. A Proportional-Integral-Derivative (PID) controller has been designed for pitch control of hybrid airship including collision avoidance in the pitch up and pith down path. A Hardware-In-the-Loop (HIL) solution also provided for the designed PID controller on UNO kit. Open loop and closed loop stability analysis is done for the longitudinal dynamics of winged small sized hybrid airship. Internal model compensator is required to make overall system as a stable system. A Simulink model for longitudinal dynamics of the hybrid airship with controllers and compensators is developed and result is analyzed and verified with open literature. Overshoot of u is the problem, although it settles to zero trim values within 30 sec. Except that all other parameters of longitudinal dynamics settle to equilibrium points within few seconds. Altair Embed software is used for HIL development. [ABSTRACT FROM AUTHOR]

In this paper, the rules and design criterion of airship stability, modes and aerodynamic parameters are studied by varying the hull and fin parameters using systematic modeling. The exposed airship fin surface area is demonstrated to be a critical factor affecting the change of the airship stability and mode states. Based on this factor, the design criterion of stability is confirmed and updated. It is demonstrated that when the normalized exposed airship fin surface area exceeds 0.08, the airship becomes stable. It is also discovered that the necessary exposed fin area required to maintain stability could be reduced by placing the fins farther rearward. Additionally, as the exposed fin area increases, there exists a qualitative change of modes wherein the two lateral exponential modes of the airship may converge into one oscillatory mode. Lastly, attention is also given to two aerodynamic parameters. Because it is found that the stability boundary falls in relatively fixed ranges of the two parameters, they can also be used to estimate airship stability states, whereas the qualitative change boundary of the modes falls in a varying range and a similar conclusion cannot be drawn. [ABSTRACT FROM AUTHOR]

Installing a precooler behind the intake is an effective approach for hypersonic air-breathing pre-cooled engine to cool the hot incoming air. Synergetic airbreathing rocket engine is a revolutionary hypersonic air-breathing pre-cooled engine with complex thermodynamic cycle i.e. air cycle, helium cycle. Air/helium precooler is a key component and its configuration and operating condition have great effect on the performance characteristics of air-breathing pre-cooled engine. Thus, the minimum periodic flow and heat transfer model of the precooler are established. The effects of key parameters on the heat transfer performance of precooler are numerically studied. The results indicate that: when the tube row number increases from 7 to 15, the average heat transfer coefficient of air side decreases by 57%, the heat exchange rate increases by 19%, and effectiveness increases by 18.4%. The tube transverse pitch can enhance the heat transfer coefficient of air and helium side, while the heat exchange rate decreases by 33 % when the tube transverse pitch increases from 1.5 to 3.5. The helium inlet velocity can improve the heat transfer performance of precooler and reduce the flow resistance of air side. [ABSTRACT FROM AUTHOR]

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The stratospheric airship is a type of aerostat that uses solar energy as its power source and can fly continuously for months or even years in near space. The rapid and accurate prediction of the output power of its solar array is the key to maintaining energy balance and extending flight time. This paper establishes an online learning model for predicting the output power of the solar array of stratospheric airships. The readings of radiometers arranged on the surface of the airship are used as features for training the model. The parameters of the model can be updated in real-time during the flight process without retraining the entire model. The effect of radiometer placement on the model accuracy was also analyzed. The results show that for the continuous flight of 40 days, the online learning model can achieve an accuracy of 88% after training with 10 days of flight data and the accuracy basically reaches its highest level after 20 days. In addition, placing the radiometers at the four corners of the array can achieve a higher prediction accuracy of 95%. The online model can also accurately identify and reflect the effect of module efficiency attenuation or damage and maintain high accuracy. [ABSTRACT FROM AUTHOR]

The tropospheric hydroxyl radical (TOH) is a key player in regulating oxidation of various compounds in Earth's atmosphere. Despite its pivotal role, the spatiotemporal distributions of OH are poorly constrained. Past modeling studies suggest that the main drivers of OH, including NO2, tropospheric ozone (TO3), and H2O(v), have increased TOH globally. However, these findings often offer a global average and may not include more recent changes in diverse compounds emitted on various spatiotemporal scales. Here, we aim to deepen our understanding of global TOH trends for more recent years (2005–2019) at 1×1 degrees. To achieve this, we use satellite observations of HCHO and NO2 to constrain simulated TOH using a technique based on a Bayesian data fusion method, alongside an interpretable machine learning module named ECCOH, which is integrated into NASA's GEOS global model. This innovative module helps efficiently predict the convoluted response of TOH to its drivers/proxies. Aura Ozone Monitoring Instrument (OMI) NO2 observations suggest that the simulation has high biases over biomass burning activities in Africa and Eastern Europe, resulting in overestimation of up to 20 % in TOH, regionally. OMI HCHO primarily impacts oceans where TOH linearly correlates with this proxy. Five key parameters including TO3, H2O(v), NO2, HCHO, and stratospheric ozone can collectively explain 65 % of variance in TOH trends. The overall trend of TOH influenced by NO2 remains positive, but it varies greatly because of the differences in the signs of anthropogenic emissions. Over oceans, TOH trends are primarily positive in the northern hemisphere, resulting from the upward trends in HCHO, TO3, and H2O(v). Using the present framework, we can tap the power of satellites to quickly gain a deeper understanding of simulated TOH trends and biases. [ABSTRACT FROM AUTHOR]

Satellite-based estimations of dry-air column-averaged mixing ratios of methane (XCH4) contribute to a better understanding of changes in CH4 emission sources and variations in its atmospheric growth rates. High accuracy of the satellite measurements is required, and therefore, extensive validation is performed, mainly against the Total Carbon Column Observing Network (TCCON). However, validation opportunities at open-ocean areas outside the coastal regions are sparse. We propose a new approach to assess the accuracy of satellite-derived XCH4 trends and variations. We combine various ship and aircraft observations with the help of atmospheric chemistry models, mainly used for the stratospheric column, to derive observation-based XCH4 (obs. XCH4). Based on our previously developed approach for the application to XCO2 , we investigated three different advancements, from a simple approach to more elaborate approaches (approaches 1, 2, and 3), to account for the higher tropospheric and stratospheric variability in CH4 as compared to CO2. Between 2014 and 2018, at 20–40° N of the western Pacific, we discuss the uncertainties in the approaches and the derived obs. XCH4 within 10° by 20° latitude–longitude boxes. Uncertainties were 22 ppb (parts per billion) for approach 1, 20 ppb for approach 2, and 16 ppb for approach 3. We analyzed the consistency with the nearest TCCON stations and found agreement of approach 3 with Saga of 1±12 ppb and -1±11 ppb with Tsukuba for the northern and southern latitude box, respectively. Furthermore, we discuss the impact of the modeled stratospheric column on the derived obs. XCH4 by applying three different models in our approaches. Depending on the models, the difference can be more than 12 ppb (0.6 %), showing the importance for the appropriate choice. We show that our obs. XCH4 dataset accurately captures seasonal variations in CH4 over the ocean. Using different retrievals of the Greenhouse Gases Observing Satellite (GOSAT) from the National Institute for Environmental Studies (NIES), the RemoTeC full-physics retrieval operated at the Netherlands Institute for Space Research (SRON), and the full-physics retrieval of the University of Leicester (UoL-OCFP), we demonstrate the applicability of the dataset for satellite evaluation. The comparison with results of approach 3 revealed that NIES showed a difference of - 0.04 ± 13 ppb and strong scatter at 20–30° N, while RemoTeC and OCFP have a rather systematic negative bias of - 12.1 ± 8.1 and - 10.3 ± 9.6 ppb. Our new approach to derive XCH4 reference datasets over the ocean can contribute to the validation of existing and upcoming satellite missions in future. [ABSTRACT FROM AUTHOR]

Summary: This paper presents a near‐space communication system (NSCS) using advanced deployment strategies to gain high throughput. The airships are deployed according to the user's location, assuming robust backbone network characteristics such as signal path loss, fading factor, routing efficiency, and safety issues among bi‐connected airships. Due to the independent flying nature of airships, it is very attractive to deploy them as aerial base stations and construct airborne networks to provide service for on‐ground users. However, it is quite challenging to optimally deploy multiple airships for on‐demand coverage while maintaining the connectivity among airships. A balance between the network parameters, i.e., capacity and coverage area, should be maintained for optimal deployment of the airships. We have derived the maximum throughput of NSCS, including system parameters, as a multiobjective optimization problem subjected to efficient routing protocol and safety constraints. A decomposition‐based advanced multiobjective evolutionary algorithm (AMOEA/D) is adopted to solve the deployment optimization problem. The proposed algorithm is motivated by the non‐dominated solutions that maintain population diversity over the variable space. Two designed test problems, that is, the L‐shaped hotspot problem and nine hotspot problems, are also investigated. Numerical results show that the proposed method improves the system performance compared with benchmark external archive‐guided MOEA/D (EGA‐MOEA/D) and non‐dominated sorted genetic algorithms (NSGA‐II) by 10.46% and 3.84%, respectively. [ABSTRACT FROM AUTHOR]

The calculation of a cockpit's transient thermal load is important for determining the capacity of the cockpit environmental control system, ensuring the safety of electronic equipment and increasing the health and comfort of cockpit occupants. According to the structural parameters of the cockpit of a sightseeing airship, a physical model is established. The turbulence model and calculation method are selected and verified. The transient thermal load within full flight envelope, the cockpit thermal loads at different times of the day, and the cockpit thermal loads under different free-flow velocities are obtained based on the Computational Fluid Dynamics (CFD) method. The cockpit transient thermal loads during different seasons are also obtained. The results show that solar radiation has a great influence on the cockpit transient thermal load. As the flight altitude increases, the thermal load decreases from 8.8 kW (H = 0 m) to 4.7 kW (H = 3000 m). With the change in the solar radiation intensity and solar radiation angle, the thermal load increases considerably, from 2.2 kW (8:00 a.m.) to 5.4 kW (12:00 a.m.). The influence of the free-flow velocity is not very obvious at an altitude of 3000 m, as discussed in this study. The influence of seasons is significant. Finally, the influence of the solar absorptivity and infrared emissivity of the cockpit surface material are studied, and the temperature distribution on the cockpit's surface is determined. [ABSTRACT FROM AUTHOR]