Spatial-Temporal Patterns of Air Pollutant Emissions From Landing and Take-Off Cycles in the Yangtze River Delta of China During the COVID-19 Outbreak

The global aviation industry has been experiencing catastrophic disruption since the beginning of 2020 due to the unprecedented impact of the COVID-19 pandemic on air traffic. Although the decline in regular commercial air travel has caused tremendous economic loss to aviation stakeholders, it has also led to the reduction in the amount of recorded air pollutants. Most of the aircraft emissions are released during the cruise phase of flight, however they have relatively small impact on humans due to the fact that those emissions are released directly into the upper troposphere and lower stratosphere. Therefore, the scope of this study is to investigate the ground-level aircraft emissions from landing and take-off (LTO) cycles, as they have a greater influence on the ambient environment of the airports in a specific region. In this paper, we study the variation of typical air pollutant concentrations (i.e., HC, CO, and NOx) from the LTO cycles during the outbreak of COVID-19 pandemic in both temporal and spatial scales. These ground-level emissions are estimated for the 22 airports in the Yangtze River Delta, China. The results indicate that the variation pattern of the three air pollutants were significantly influenced by the dramatic onset of the COVID-19 pandemic, as well as the pertinent policies to suppress the spread of the virus. The results also reveal non-uniform distribution of the emission quantified at different airports. It is noticeable that the emission quantity generally declined from the east coast to the central and western part of the research region. Furthermore, discrepancies in the target markets also create disparities in the variation pattern of the emissions at different airports under the context of COVID-19.

Structural health monitoring of beams with moving oscillator: theory and laboratory

In this paper, a new intelligent portable mechanical system is introduced experimentally and theoretically to detect damage employing the fuzzy-genetic algorithm and EMD. For this purpose, the acceleration-time history is obtained from three points of a simply-supported beam utilizing accelerometer sensors. The gained signal is decomposed into small components by using an EMD method. Each decomposed component contains a specific frequency range. Finally, the proposed algorithm is designed to find the location and severity of damage through the frequency variation pattern among the safe and the damaged beam.

Influence of Geographical and Climatic Factors on Quercus variabilis Blume Fruit Phenotypic Diversity

Quercus variabilis Blume is one of the most ecologically valuable tree species in China and is known to have adaptive mechanisms to climate change. Our objective was to quantify the variation pattern in the fruit morphology of Q. variabilis. Fruit samples were collected from 43 natural populations in autumn of 2019. Our results indicated that the coefficient of variation (CV) of the fruit length (FL) and fruit width (FW) were 10.08% and 11.21%, respectively. There were significant differences in the FL, FW, and fruit length-to-width ratios (FL/FW) among the studied populations. Also, there was a significant positive correlation between the FW and FL. The FL decreased with increasing precipitation in the wettest quarter (PWQ). A concave trend was observed in the variations in FL with the equivalent latitude (ELAT), longitude (LON), annual mean air temperature (MAT), and annual precipitation (AP). A similar concave trend was observed for the FL/FW with LON, MAT, and AP. A positive correlation was observed between the FW, FL and FL/FW, and the ELAT. The cluster analysis revealed five groups of the 43 natural populations. Our study findings suggests that Q. variabilis has high levels of phenotypic plasticity for geographical and climatic factors.

Phase-delay Induced Variation of Synchronization Bandwidth and Frequency Stability in a Micromechanical Oscillator

Phase feedback is commonly utilized to set up a synchronized MEMS oscillator for high performance sensor applications. It's a consensus that the synchronization region varies with phase delay with a `Anti-U' mode within 0 to pi and phase delay is typically fixed on pi/2 to achieve maximum synchronization range and best frequency stability. In this paper, phase-delay induced variation of synchronization bandwidth and frequency stability in a micromechanical oscillator is investigated analytically and experimentally. A self-sustained oscillator is built by applying phase feedback to an electrostatically actuated micro-beam resonator and synchronization phenomenon is observed after coupling it to a weak external periodic excitation. The analytical expression for predicting the synchronization bandwidth with phase delay is derived based on the dynamic model, from which three different types (`U', `Anti-U' and `M') of variation pattern of synchronization bandwidth are observed as feedback tuning. The variation of frequency stability along phase delay is also studied. The synchronization bandwidth and the frequency stability have exactly opposite variation pattern with phase delay in linear oscillators while they are totally consistent in nonlinear oscillators. Experimental tests in vacuum environment are carried out to validate the analytical observations. Our work presented here provides a precise way for achieving best performance of a synchronized MEMS oscillator in the sensor application.

Entropy Generation Analysis and Cooling Time Estimation for a Rotating Vertical Hollow Tube in the Air Medium

An objective function combining the first and second laws of thermodynamics has been employed to delineate the thermodynamic performance on mixed convection around a vertical hollow, rotating cylinder within the laminar range with the variation of Rayleigh number (104 ≤ Ra ≤ 108), Reynolds number (ReD < 2100), and aspect ratio (1 ≤ L/D ≤ 20). Entropy generation in the system is predominantly triggered by heat transfer in comparison to fluid friction. The irreversibility incurred progressively increases with an increase in Ra and ReD. The variation pattern of (I/Q)Rotation/(I/Q)Non−Rotation has been demonstrated to find out the optimized regime where heat transfer is maximum within the laminar range. The contribution of fluid friction irreversibility toward total irreversibility rises abruptly with an increase in ReD for all cases of L/D and Ra. To demonstrate this study's thermodynamic characteristics, the static temperature contours as well as the contours of entropy generation have been represented pictorially. The estimation of cooling time has been reported by using the method of lumped capacitance.