Recently, secondary organic aerosols (SOAs) generated from anthropogenic volatile organic compounds have been proposed as a possible source of light-absorbing organic compounds, "brown carbon," in ...the urban atmosphere. However, the atmospheric importance of these SOAs remains unclear due to limited information about their optical properties. In this study, the complex refractive index (RI, m = n-ki values at 405, 532, and 781 nm of the SOAs generated during the photooxidation of toluene (toluene-SOAs) under a variety of initial nitrogen oxide (NOx = NO + NO2 ) conditions were examined by photoacoustic spectroscopy (PAS) and cavity ring-down spectroscopy (CRDS). The complex RI-values obtained in the present study and reported in the literature indicate that the k-value, which represents the light absorption of the toluene-SOAs, increased to shorter wavelengths at <532 nm, and the n-value also increased to shorter wavelengths from 781 to 355 nm. The k-values at 405 nm were found to increase from 0.0018 to 0.0072 with increasing initial NOx concentration from 109 to 571 ppbv. The nitrate to organics ratio of the SOAs determined using a high-resolution time-of-flight aerosol mass spectrometer (H-ToF-AMS) also increased with increasing initial NOx concentration. The RI-values of the SOAs generated during the photooxidation of 1,3,5-trimethylbenzene in the presence of NOx (1,3,5-TMB-SOAs) were also determined to investigate the influence of the chemical structure of the precursor on the optical properties of the SOAs, and it was found that the light absorption of the 1,3,5-TMB-SOAs is negligible at all of the wavelengths investigated (405, 532, and 781 nm). These results can be reasonably explained by the hypothesis that nitroaromatic compounds, such as nitrocresols, are the major contributors to the light absorption of the toluene-SOAs. Using the obtained RI-values, mass absorption cross sections of the toluene-SOAs at 405 nm were estimated to be 0.08-0.52 m2 g-1 under typical conditions in an urban atmosphere during the daytime. These results indicate that light absorption by the SOAs potentially contributes to the radiation balance at ultraviolet wavelengths below ~400 nm, specifically when the mass concentrations of the anthropogenic SOAs are significant compared with other light-absorbing particles.
Characteristic features of the Venus ionosphere below the V1 base, named as V0 layer, have been studied using the Radio Science payload onboard Akatsuki orbiter. An ionospheric layer below the V1 ...base is known to be present in the Venus ionosphere but found to be geographically localized, seen mostly during the daytime between 55 and 90° solar zenith angle (SZA). We, for the first time, show its presence at different latitudes and SZA, including near the equator during the local noon and post‐sunset hours. The maximum density of this layer was ∼4 × 1010 m−3 at the altitude range of 110 ± 4 km. In the absence of in‐situ measurements, it's difficult to comment on the origin but the presence of such layers during post‐sunset hours suggests their meteoric origin as the observed altitudes are consistent with the height range predicted by the meteor models. Other possible sources of such layers are also discussed.
Plain Language Summary
Akatsuki orbiter has been conducting radio occultation (RO) measurements since 2016 to study the atmosphere and ionosphere of Venus using an onboard Radio Science experiment. A total of 34 electron density profiles have been obtained so far, among which 25 are from the dayside. There are six profiles that show an enhancement in the electron density below 120 km altitude, the base of V1 layer. We report the presence of such layers near the equatorial region, both during the day and night time. We have named it the V0 layer because they are no longer geographically localized phenomena, earlier believed to be. A most probable explanation for the presence of this layer is the ionization of metallic molecules associated with meteor showers. As photo‐ionization is a main source of ions in the Venus ionosphere, its presence during the post‐sunset hours supports the idea of their meteoric origin as the night side of Venus receives no solar radiation. However, to confirm V0 as a sporadic or consistent layer, we need to investigate with in situ measurements supported by more frequent RO experiments.
Key Points
First observations of V0 layer in the Venus ionosphere near the subsolar point at solar zenith angle (SZA) ∼5°, and well past the solar terminator at SZA ∼108°
First observation of V0 layer at the equator during the local noon
Akatsuki radio science measurements, for the first time, show that such layers are not SZA dependant
This study investigates the potential impact of Solar Energetic Particles (SEPs) on the V0 layer of the Venus ionosphere. Electron density profiles obtained from radio occultation experiments ...conducted by the Venus Express (VEX) and Akatsuki missions were utilized for this purpose. Background data from the Analyzer of Space Plasma and EneRgetic Atoms (ASPERA‐4) aboard VEX were used to detect SEP events. Additionally, observations from the Space Environment Monitor (SEM) suite onboard the Geostationary Operational Environmental Satellite (GOES) during alignments of Venus, Earth, and the Sun were also considered. Our findings indicate that while SEPs may contribute to the formation of the V0 layer, they are not the main driving force in the Venusian ionosphere.
Plain Language Summary
The Venusian ionosphere shows sporadic enhancements in electron density around 110 km altitude. Despite extensive investigation, the exact cause of its sporadic presence remains elusive. Previous studies have explored various theories, including meteoric influences, gravity waves, and the impact of minor atmospheric constituents such as NO, O2, C, Ar, H2, and H. However, none have conclusively explained its formation mechanism. In this study, we have investigated the potential influence of Solar Energetic Particles (SEPs) on the V0 layer. By analyzing electron density profiles obtained from VEX/Akatsuki missions, hot plasma measurements by ASPERA‐4 onboard VEX, and SEM suite onboard GOES to identify SEP events, we surmise that while SEPs may contribute to the formation of the V0 layer, they are not the primary driving force in the Venusian ionosphere.
Key Points
The Impact of solar energetic particle (SEP) events on the formation of V0 layers in the Venusian ionosphere has been explored
Enhanced ionization is seen above the V2 layer peak whenever a V0 layer seen in the Venus ionosphere
SEPs and enhanced ionization at 110 km altitudes, however, are not correlated
The epithelial-mesenchymal transition (EMT) is a crucial morphological event that occurs during the progression of epithelial tumors. EMT can be induced by transforming growth factor β (TGF-β) in ...certain kinds of cancer cells through the induction of Snail, a key regulator of EMT. We have previously found that TGF-β remarkably induces Snail expression in cooperation with Ras signals; however, the underlying mechanism of this synergism has not yet been determined. Here, we demonstrate that signal transducer and activator of transcription 3 (STAT3) acts as a mediator that synergizes TGF-β and Ras signals. The overexpression of STAT3 enhanced Snail induction, whereas siRNA-mediated knockdown of STAT3 inhibited it. The STAT3-YF mutant, which has Tyr 705 substituted with Phe, did not enhance Snail induction. Several STAT3 mutants lacking transcriptional activity also failed to enhance it; however, the putative STAT3-binding elements in the Snail promoter regions were not required for STAT3-mediated Snail induction. Protein inhibitor of activated STAT3 (PIAS3) inhibited the enhanced Snail promoter activity induced by TGF-β and Ras. The interaction between PIAS3 and STAT3 was reduced by TGF-β in cells harboring oncogenic Ras, whereas TGF-β promoted the binding of PIAS3 to Smad3, a crucial mediator of TGF-β signaling. Therefore, these findings suggest that STAT3 enhances Snail induction when it is dissociated from PIAS3 by TGF-β in cooperation with Ras signals.
Using measurements from radio science experiments onboard Venus Express and Akatsuki orbiter, we explore factors that control the occurrence and spatial structure of the electron density enhancement ...at lower altitudes (V0 layer) in the Venus ionosphere. Results suggest that the Gravity Waves (GWs) play a crucial role in determining the shape of the V0 layer. For solar zenith angle (SZA) less than 40°, when the average gravity wave potential energy (AGPE) is less than 4.7 J/kg, V0 has a single well‐defined peak. For higher AGPE, the V0 peak height gets perturbed and exhibits a wave‐like structure. For SZA >40°, and AGPE >4.7 J/kg, mostly wave‐like feature at the base of the V0 layer emerges. We surmise that although GW do not control the formation of a V0 layer, they likely control its shape and occurrence altitude.
Plain Language Summary
Venus is known to have a peak in the plasma density at ∼140 km altitude (V2 layer), and a secondary permanent peak at ∼127 km (V1 layer). A sporadic enhancement in the electron density below 120 km altitude (now known as V0 layer) has also been reported. Earlier believed to be geographically localized, Akatsuki measurements have shown its presence over all the latitudes including at the deep equator during local noon hours. Though the origin of such enhancement in plasma density forming a V0 layer is still not clear, we have explored how the forcing from the lower atmosphere impacts the V0 layer characteristics. Our results suggest that the enhancement in the AGPE above a certain threshold value perturbs the plasma of the V0 layer and plays a pivotal role in defining its shape, but it does not impact the formation of this layer. We also observe the local time effect on the frequency of high AGPE leading to varying V0 layer features.
Key Points
The first study on the impact of gravity waves on the shape and characteristic features of V0 layers in the Venusian ionosphere
Despite not necessarily being the cause of the V0 layer, gravity waves are seen as a crucial factor influencing its shape and structure
A local time dependence on the structure of the V0 layer is also observed
Background and Objective
Porphyromonas gingivalis is considered a major pathogen of chronic periodontitis, which also may be implicated with systemic diseases such as atherosclerosis. Secreted ...cysteine proteases, gingipains Rgp and Kgp, are essential for P. gingivalis virulence. Some polyphenols and flavonoids are known to inhibit gingipain activity and interfere with biofilm formation by P. gingivalis. Many bioactive compounds have been isolated from Epimedium species, but availability of these compounds on gingipains and P. gingivalis is still unclear. Therefore, the aim of this study was to evaluate natural products from medical plants to develop a new therapeutic agent against periodontal disease.
Material and Methods
Prenylated flavonoids were isolated from Epimedium species plant using column chromatographies. The inhibitory effect of the prenylated flavonoids against protease activity of gingipains were examined using purified gingipains and fluorogenic substrates. Anti‐P. gingivalis activity was evaluated to analyze planktonic growth and biofilm formation in brain heart infusion medium in the presence of the prenylated flavonoids.
Results
We isolated 17 prenylated flavonoids (Limonianin, Epimedokoreanin B, etc.) from Epimedium species. We found that some prenylated flavonoids inhibited gingipain activity in a non‐competitive manner with Ki values at μm order. The prenylated flavonoids also hindered growth and biofilm formation of P. gingivalis, in a manner independent of gingipain inhibition by the compounds.
Conclusion
The results indicated an inhibitory effect of the prenylated flavonoids against P. gingivalis and would provide useful information for future development of periodontitis treatment that suppresses gingipains, P. gingivalis growth and biofilm formation.
ABSTRACT
The solar inner corona is a region that plays a critical role in energizing the solar wind and propelling it to supersonic and supra-Alfvénic velocities. Despite its importance, this region ...remains poorly understood because of being least explored due to observational limitations. The coronal radio-sounding technique in this context becomes useful as it helps in providing information in parts of this least explored region. To shed light on the dynamics of the solar wind in the inner corona, we conducted a study using data obtained from coronal radio-sounding experiments carried out by the Akatsuki spacecraft during the 2021 Venus-solar conjunction event. By analysing X-band radio signals recorded at two ground stations (Indian Deep Space Network in Bangalore and Usuda Deep Space Center in Japan), we investigated plasma turbulence characteristics and estimated flow speed measurements based on isotropic quasi-static turbulence models. Our analysis revealed that the speed of the solar wind in the inner corona (at heliocentric distances from 5 to 13 solar radii), ranging from 220 to 550 km s−1, was higher than the expected average flow speeds in this region. By integrating our radio-sounding results with extreme ultraviolet (EUV) images of the solar disc, we gained a unique perspective on the properties and energization of high-velocity plasma streams originating from coronal holes. We tracked the evolution of fast solar wind streams emanating from an extended coronal hole as they propagated to increasing heliocentric distances. Our study provides unique insights into the least-explored inner coronal region by corroborating radio-sounding results with EUV observations of the corona.
Terrestrial exoplanets orbiting within or near their host stars' habitable zone are potentially apt for life. It has been proposed that time-series measurements of reflected starlight from such ...planets will reveal their rotational period, main surface features and some atmospheric information. From imagery obtained with the Akatsuki spacecraft, here we show that Venus' brightness at 283, 365, and 2020 nm is modulated by one or both of two periods of 3.7 and 4.6 days, and typical amplitudes <10% but occasional events of 20-40%. The modulations are unrelated to the solid-body rotation; they are caused by planetary-scale waves superimposed on the super-rotating winds. Here we propose that two modulation periods whose ratio of large-to-small values is not an integer number imply the existence of an atmosphere if detected at an exoplanet, but it remains ambiguous whether the atmosphere is optically thin or thick, as for Earth or Venus respectively. Multi-wavelength and long temporal baseline observations may be required to decide between these scenarios. Ultimately, Venus represents a false positive for interpretations of brightness modulations of terrestrial exoplanets in terms of surface features.
Longwave Infrared Camera (LIR) on board Akatsuki first revealed the global structure of the thermal tides in the upper cloud layer of Venus. The data were acquired over three Venusian years, and the ...analysis was done over the areas from the equator to the midlatitudes in both hemispheres and over the whole local time. Thermal tides at two vertical levels were analyzed by comparing data at two different emission angles. Dynamical wave modes consisting of tides were identified; the diurnal tide consisted mainly of Rossby‐wave and gravity‐wave modes, while the semidiurnal tide predominantly consisted of a gravity‐wave mode. The revealed vertical structures were roughly consistent with the above wave modes, but some discrepancy remained if the waves were supposed to be monochromatic. In turn, the heating profile that excites the tidal waves can be constrained to match this discrepancy, which would greatly advance the understanding of the Venusian atmosphere.
Plain Language Summary
On Venus, the atmosphere circulates 60 times faster than the solid body of Venus; this phenomenon is called “superrotation,” and it is one of the mysteries of the Venusian atmosphere. To maintain the fast circulation, thermal tides, which are global‐scale atmospheric waves excited by solar heating, have been considered a very important candidate because they have the ability of accelerating the atmosphere through propagating. A midinfrared camera onboard the Japanese Venus orbiter, Akatsuki, can capture temperature perturbations due to the thermal tides in the upper cloud level (60‐ to 70‐km altitude), and it revealed their global and vertical structures with a long‐term observation (more than three Venusian years) for the first time. Interestingly, we found that the location of the maximum temperature at the cloud top level was different from noon where solar energy input is at a maximum. In addition, the location was shifted toward the morning side as the sensing altitude increased. This finding is an evidence of the vertical traveling of the thermal tides, indicating the wave's atmospheric acceleration.
Key Points
Akatsuki/LIR revealed the global structures of thermal tides across the equator in the upper cloud layer of Venus for the first time
Using the emission angle dependence of LIR's sensing altitude, upward propagation of the semidiurnal tide was confirmed
Wave types consisting of the thermal tides were identified
The existence of large stationary gravity waves was discovered during Akatsuki's first observation sequence in 2015. In this study, the further detection of large stationary gravity waves in ...brightness temperature images over a 1.5 year period is reported. The waves periodically appeared mostly above four specific highland regions in the low latitudes when these regions were in the local afternoon. The wave amplitudes attenuated after the wave locations passed beyond the evening terminator, and the locations of the waves tended to slowly drift eastward over their lifetimes. The appearances of stationary waves depend not only on surface topography but also on latitude and local time, suggesting that solar heating during the daytime and atmospheric structure affected by solar heating may control the excitation and propagation of stationary waves.
Plain Language Summary
The Japanese Venus satellite “Akatsuki” has repeatedly found large atmospheric waves with north‐south lengths, which sometimes reach more than 10,000 km at the cloud top level on Venus (altitude ~70 km). These waves have repeatedly appeared above the Venusian highlands in low latitudes, such as Aphrodite Terra. Interestingly, the waves appeared and became clearer each time the highlands passed from noon to evening; therefore, they can be regarded as “daily” Venusian phenomena. Despite westward wind speeds reaching 100 m s−1 at the cloud top level (known as atmospheric superrotation), the east‐west propagation speeds of the large waves were nearly zero, and the waves stayed above their initial locations (stationary). This means that the origin of the waves could be the highland terrains below. Because waves can transport energy via propagation, stationary waves may transport atmospheric energy from the lower atmosphere to the cloud top level and may affect the speed of the superrotation. The existence and regular appearance of the large stationary waves indicate a continuous interaction between the lower and upper atmospheres on Venus via wave propagation, which provides a novel perspective of the Venusian atmosphere.
Key Points
Stationary gravity waves with large horizontal extent at the cloud top level of Venus have been repeatedly identified
The locations of these waves show a clear connection to Venusian highlands, and wave amplitude depends on the local time at the highlands
Monitoring of the stationary waves would bring information of the Venusian atmosphere along the wave propagation paths
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