Abstract
Following the pulsation spectrum of a white dwarf through the heating and cooling involved in a dwarf nova outburst cycle provides a unique view of the changes to convective driving that ...take place on timescales of months versus millennia for nonaccreting white dwarfs. In 2019 January the dwarf nova V386 Ser (one of a small number containing an accreting, pulsating white dwarf) underwent a large-amplitude outburst. Hubble Space Telescope ultraviolet spectra were obtained 7 and 13 months after outburst along with optical ground-based photometry during this interval and high-speed photometry at 5.5 and 17 months after outburst. The resulting spectral and pulsational analysis shows a cooling of the white dwarf from 21,020 to 18,750 K (with a gravity
log
(
g
)
=
8.1
) between the two UV observations, along with the presence of strong pulsations evident in both UV and optical at a much shorter period after outburst than at quiescence. The pulsation periods consistently lengthened during the year following outburst, in agreement with pulsation theory. However, it remains to be seen if the behavior at longer times past outburst will mimic the unusual nonmonotonic cooling and long periods evident in the similar system GW Lib.
Driving fatigue is a serious issue for the transportation sector, decreasing the driver's performance and increasing accident risk. This study aims to investigate how fatigue mediates the ...relationship between the nature of work factors and driving performance. The approach included a review of the previous studies to select the dimensional items for the data collection instrument. A pilot test to identify potential modification to the questionnaire was conducted, then structural equation modelling (SEM) was performed on a stratified sample of 307 drivers, to test the suggested hypotheses. Based on the results, five hypotheses have indirect relationships, four of which have a significant effect. Besides, the results show that driving fatigue partially mediates the relationship between the work schedule and driving performance and fully mediates in the relationship between work activities and driving performance. The nature of work and human factors is the most common reason related to road accidents. Therefore, the emphasis on driving performance and fatigue factors would thereby lead to preventing fatal crashes and life loss.
Abstract
Increased atmospheric evaporative demand has important implications for humans and ecosystems in water-scarce lands. While temperature plays a significant role in driving evaporative demand ...and its trend, other climate variables are also influential and their contributions to recent trends in evaporative demand are unknown. We address this gap with an assessment of recent (1980–2020) trends in annual reference evapotranspiration (ETo) and its drivers across the continental United States based on five gridded datasets. In doing so, we characterize the structural uncertainty of ETo trends and decompose the relative influences of temperature, wind speed, solar radiation, and humidity. Results highlight large and robust changes in ETo across much of the western United States, centered on the Rio Grande region where ETo increased 135–235 mm during 1980–2020. The largest uncertainties in ETo trends are in the central and eastern United States and surrounding the Upper Colorado River. Trend decomposition highlights the strong and widespread influence of temperature, which contributes to 57% of observed ETo trends, on average. ETo increases are mitigated by increases in specific humidity in non-water-limited regions, while small decreases in specific humidity and increases in wind speed and solar radiation magnify ETo increases across the West. Our results show increases in ETo across the West that are already emerging outside the range of variability observed 20–40 years ago. Our results suggest that twenty-first-century land and water managers need to plan for an already increasing influence of evaporative demand on water availability and wildfire risks.
Significance Statement
Increased atmospheric thirst due to climate warming has the potential to decrease water availability and increase wildfire risks in water-scarce regions. Here, we identified how much atmospheric thirst has changed across the continental United States over the past 40 years, what climate variables are driving the change, and how consistent these changes are among five data sources. We found that atmospheric thirst is consistently emerging outside the range experienced in the late twentieth century in some western regions with 57% of the change driven by temperature. Importantly, we demonstrate that increased atmospheric thirst has already become a persistent forcing of western landscapes and water supplies toward drought and will be an essential consideration for land and water management planning going forward.
Emissions of NH3 and nine nitrogen-containing volatile organic compounds (NVOCs) (C1–3-amines, C1–3-amides, and C1–3-imines) from motor vehicles powered by gasoline, diesel, and natural gas under ...low-speed driving conditions from roadside in situ measurements were characterized using a water-cluster chemical ionization mass spectrometer and trace gas monitors. The total emission strength of diesel trucks was the greatest followed by those of gasoline cars and natural gas cars. NH3 emission per vehicle was found to be 2–3 orders of magnitude greater than that of all NVOCs, regardless of the type of vehicle. Although much lower than the emissions of amides or imines, emissions of amines were sufficient to produce atmospheric concentrations exceeding the threshold level for amines to enhance atmospheric nucleation by several orders of magnitude. Different engine emission reduction technologies (e.g., three-way catalytic converter vs selective catalytic reduction) can lead to different NH3 and NVOC emission profiles. During the lifetime of a vehicle, its emission level was most likely to increase with its mileage. Source profiles of NH3 and NVOC emissions from the three types of vehicles were also obtained from the measurements. These profiles can be a valuable contribution to the air pollution management system in terms of source apportionment, elucidating the emission contributions from a specific type of vehicle.
Magnetic reconnection occurring between the interplanetary magnetic field (IMF) and the dayside magnetopause causes a circulation of magnetic flux and plasma within the magnetosphere, known as the ...Dungey cycle. This circulation is transmitted to the ionosphere via field‐aligned currents (FACs). The magnetic flux transport within the Dungey cycle is quantified by the cross‐polar cap potential (CPCP or transpolar voltage). Previous studies have suggested that under strong driving conditions the CPCP can saturate near a value of 250 kV. In this study we investigate whether an analogous saturation occurs in the magnitudes of the FACs, using observations from the Active Magnetosphere and Planetary Electrodynamics Response Experiment. The solar wind speed, density and pressure, the Bz component of the IMF, and combinations of these, were compared to the concurrent integrated current magnitude, across each hemisphere. We find that FAC magnitudes are controlled most strongly by solar wind speed and the orientation and strength of the IMF. FAC magnitude increases monotonically with solar wind driving but there is a distinct knee in the variation around IMF Bz = −10 nT, above which the increase slows.
Plain Language Summary
During extreme space weather events, the threat to space‐based and surface infrastructure has become of increasing concern within the past 2 decades. These space weather events are directly responsible for electrical currents flowing in the ionosphere that produce potentially dangerous magnetic field perturbations on the ground. With this motivation, we use satellite magnetometer data in order to gain greater insight into the field aligned current systems present above both poles of the Earth. With many mechanisms and processes which govern the magnitude of these currents (and associated potentials) still being widely disputed, we hope to offer verification of whether or not these currents saturate at high solar wind driving, in order to create a clearer picture of the behavior of these systems from nominal to intense space weather conditions.
Key Points
The field‐aligned current (FAC) flow increases with increasing southward interplanetary magnetic field (IMF) Bz
There is a steeper gradient of increase for IMF Bz values below −10 nT than for that above 10 nT, for all local times
Features of polar cap potential saturation are observed in FAC data during strong southward IMF
A truck platoon is a set of virtually linked trucks that travel in tandem with small intervehicle distances. Several studies have proved that traveling in platoons can significantly improve fuel ...economy due to the reduced aerodynamic drag. However, most literature only provides scattered pieces of information regarding fuel economy in truck platoons. Therefore, a literature survey is needed to understand what has been studied and what problems remain to be further addressed. This paper presents an overview of existing studies to illustrate the state of the art about fuel savings for truck platooning. Specifically, it summarized the methodologies, the contributing factors of fuel consumption, the coordination methods to improve the platooning rate, and the look-ahead control strategies to generate fuel-efficient speed profiles for each vehicle driving in a platoon over different road grades. After that, the autonomous truck platooning was introduced, and we raised and discussed a couple of outstanding questions to be addressed in future work.
Heart rate variability and subjective workload measures are extensively used to determine workload during driving. However, the sensitivity of heart rate and workload measurements in simulated ...driving environments is mostly unknown and can significantly affect the experiment results. The objectives of this paper are to determine how heart rate variability and subjective workload are affected in simulated highway work zones and study the relationship between heart rate variability, subjective workload, and driving performance indicators in simulated driving environments. Conventional lane merge (CLM), joint lane merge (JLM) and a road with no work zone are modeled with high and low traffic densities in a full-size driving simulator. NASA-TLX subjective workload measures and heart rate variability measures of root mean square of successive heartbeat differences (RMSSD), low frequency (LF), high frequency (HF) and the ratio of low frequency to high frequency (LF/HF) are collected in 30 participants. Variability in steering angle, braking and speed are used as driving performance indicators. Results show that compared to no work zone, participants experienced higher mental, temporal, and overall workload in the CLM scenario and poorer driving performance ratings in the CLM and JLM scenarios. All workload measures except for performance were higher with high traffic density. However, heart rate variability measures were not sensitive to the differences in driving scenarios and traffic densities. Pearson correlation coefficients indicated an association between RMSSD and all the subjective workload measures (r > 0.21) except performance, and between LF, HF, and LF/HF ratio and mental workload (r > 0.21). Steering angle variability was slightly correlated with LF, HF, and LF/HF ratio (r > 0.16), but brake and speed variability were not associated with physiological outcomes.
In conclusion, the subjective workload was higher in simulated work zones and under higher traffic density, but heart rate measures were largely unaffected.
•Physiological workload was insensitive to driving in a driving simulator.•Highway work zones increased subjective workload and declined driving performance.•High traffic density increased subjective workload.•Subjective workload correlated with performance variables.
The influence of nucleation on cavitation about a sphere from inception through to supercavitation at a transcritical Reynolds number of $1.5\times 10^{6}$ is investigated experimentally. Two extreme ...free-stream nuclei populations, deplete and abundant, were investigated. Unsteady surface pressures from two sensors on opposing sides of the sphere were acquired simultaneous with high-resolution high-speed photography at cavitation numbers between 1.0 and 0.3. High-resolution spectrograms derived from these measurements reveal principally bi-modal shedding in attached and detached regimes. Correlations between unsteady pressure measurements show the high modes to be axisymmetric and low modes asymmetric. Modal topology is also discerned from the high-speed imaging. The bi-modal shedding for lower cavitation numbers is driven by coupled re-entrant jet formation and upstream shockwave propagation. The attached regime is shown to have two sub-regimes. For the abundant case, the continuous supply of activated nuclei around the sphere periphery in the first bi-modal regime has the effect of driving the high symmetric mode preferentially over the asymmetric low mode compared with the deplete case. For the first bi-modal regime, frequencies were unaffected by nucleation changes although peak responses were centred at a cavitation number of about 0.8 for the deplete and 0.825 for the abundant. For the second attached regime, where cavity lengths are of the order of the sphere size, changes in nucleation altered frequencies and amplitudes of peak unsteady pressures. For the abundant case, the continuous nuclei supply significantly reduced coherence with modal peak amplitudes reduced by an order compared with the deplete case. Continuous nuclei activation increased the probability of the high mode over the low compared with the deplete case but to a lesser extent than the first regime. Nuclei activations also significantly reduced inter-cavity and cavity durations, but not growth and collapse phases, which increased modal frequencies compared with the deplete case. The second regime asymmetric low mode topology, for both nucleation cases, is shown to be alternate shedding of oblique vortices from diametrically opposing sides of the sphere similar to low Reynolds number shedding about spheres and other axisymmetric bluff bodies in single-phase flows.
The brain is the ultimate control unit of the body. It conducts accurate, fast and reproducible calculations to control motor actions affecting mating, foraging and flight or fight decisions. ...Therefore, during evolution, better and more efficient brains have emerged. However, even simple brains are complex organs. They are formed by glial cells and neurons that establish highly intricate networks to enable information collection, processing and eventually, a precise motor control. Here, we review and connect some well‐established and some hidden pieces of information to set the focus on ion homeostasis as a driving force in glial differentiation promoting signalling speed and accuracy.
To allow axonal action potential propagation in invertebrates, glial cells can form lacunae to provide a larger extracellular ion reservoir. Voltage‐gated ion channels can cluster at the axonal plasma membrane abutting the lacunae. When the glial cell processes forming the lacunae collapse, a myelin‐like stacking of membrane sheets is formed around the axon. The low ion reservoir in the interstitial space does not favour the generation of action potentials.
Previous studies have found that Madden‐Julian Oscillation (MJO) amplitude depends on the Quasi‐Biennial Oscillation (QBO) during boreal winter. This MJO‐QBO relationship is important to realizing ...subseasonal‐to‐seasonal prediction skills, but the underlying mechanism remains unclear. It is often thought that this relationship arises through the modulation of the upper‐troposphere and lower‐stratosphere lapse rate by the QBO, but this mechanism assumes the one‐way impact of the QBO onto the MJO. Alternatively, the MJO can be hypothesized to influence the QBO by modulating stratospheric wave activity that is known to be critical to QBO dynamics. Therefore, using satellite and reanalysis data, this study examines whether MJO monthly activity can impact stratospheric wave activity and QBO downward propagation speed. The results depicted a lack of such impacts, suggesting this observed MJO‐QBO relationship cannot be driven by the MJO modulation of stratospheric wave forcing.
Plain Language Summary
The intraseasonal fluctuation in cloudiness and rainfall in the troposphere around Indonesia and nearby oceans is higher when the lower‐stratospheric winds become easterly during December, January, and February. It is important to understand why this troposphere‐stratosphere coupling occurs to extend the range of prediction skills. The changes in the lower‐stratospheric winds are associated with changes in the upper‐tropospheric temperature, which is often claimed responsible for enhancing or suppressing the development of cumulonimbus clouds and driving the documented troposphere‐stratosphere coupling. However, this previously hypothesized mechanism assumes a one‐way impact where the stratosphere impacts the troposphere. Instead, this study analyzes the potential influence of tropospheric cloudiness on the stratospheric winds. Cumulonimbus clouds can generate stratospheric waves, which are known to regulate the direction of stratospheric winds. However, our results show that the intraseasonal fluctuation of cloudiness cannot affect the stratospheric waves. It displays a lack of evidence that the intraseasonal fluctuation in cloudiness can drive its observed connection with the stratosphere.
Key Points
The Madden‐Julian Oscillation (MJO) convective activities have no significant impact on Quasi‐Biennial Oscillation (QBO) downward propagation speed
There is also no evidence that monthly MJO activities impact stratospheric wave activity that could potentially influence QBO dynamics
The documented relationship between the QBO and the MJO is not driven by MJO modifications to the stratospheric wave spectrum
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