Venus is known to have been volcanically resurfaced in the last third of solar system history and to have undergone a significant decrease in volcanic activity a few hundred million years ago. ...However, fundamental questions remain: Is Venus still volcanically active today, and if so, where and in what geological and geodynamic environment? Here we show evidence from the Venus Express Venus Monitoring Camera for transient bright spots that are consistent with the extrusion of lava flows that locally cause significantly elevated surface temperatures. The very strong spatial correlation of the transient bright spots with the extremely young Ganiki Chasma, their similarity to locations of rift‐associated volcanism on Earth, provide strong evidence for their volcanic origin and suggests that Venus is currently geodynamically active.
Key Points
VMC was able to sound Venus surface through the atmosphere transparency window
Transient bright phenomena were observed in the Ganiki Chasma zone
They are consistent with hypothesis of lava lakes on the surface
We study local bifurcations in a control system with pulse-width modulation of the first kind (PWM-1) whose state is described by a piecewise smooth mapping. It is shown that, in addition to ...classical bifurcations, the so-called border collision bifurcations, which have no analogs in smooth systems, are possible in pulsed systems. The main bifurcation transitions are described using a piecewise linear continuous mapping as a normal form.
This review considers one of the most clinically relevant representatives of the ABC transporters–multidrug resistance protein 1 (P-glycoprotein 1 or Pgp). Data on the primary, secondary, and ...tertiary structure of the protein, its synthesis and degradation, and roles of its fragments in transporter activity are presented. Particular attention is given to the mechanism of functioning of Pgp. In view of the absence of a generally recognized mechanism of action of Pgp, several existing models of the protein transport cycle are discussed. Epigenetic regulation of the
ABCB1
gene and modulation of Pgp expression by microRNAs are discussed.
The previously unknown cyclopropane spiro-fused with isoxazol-5-one ((1RS,3SR)-1-(4-methylbenzyl)-7-phenyl-5-oxa-6-azaspiro2.4hept-6-en-4-one) was synthesized from benzylideneisoxazol-5-one in 34% ...yield via double methylene transfer from diazomethane. The structure of the compound was established based on 1H, 13C, and 2D NMR spectroscopy and high-resolution mass spectrometry, and confirmed by X-ray diffraction analysis.
A one-pot procedure for the synthesis of tetrasubstituted dihydropyrimidine and pyrimidine derivatives from α-azidocinnamates was developed. The synthesis is based on the finding that the outcome of ...LED photolysis of α-azidocinnamates depends on the light wavelength employed. Blue light (455 nm) leads to the formation of 2
H
-azirines only, but violet light (395 nm), UV-A light (365 nm), or sunlight result in the transformation of the
in situ
formed 2
H
-azirines to 1,3-diazabicyclo3.1.0hex-3-enes. Under basic catalysis (DBU), the latter were isomerized to 1,6-dihydropyrimidines which were oxidized to pyrimidines using DDQ. A successful use of Cs
2
CO
3
as a base and air as an oxidant was also demonstrated.
A one-pot synthesis of tetrasubstituted dihydropyrimidine and pyrimidine derivatives was developed on the basis of UV-LED photolysis of α-azidocinnamates as a key stage.
Abstract
The influence of the energy of low-voltage discharges in the liquid phase on the directions of fragmentation of toluene is studied. The discharges were generated by a 60 V DC source with a ...capacitor of 90 μF, 20090 μF, and 40090 μF. Fragmentation of toluene leads to the formation of carbon structures on the surface of graphite electrodes and in a liquid medium. It was revealed that an increase in the power of electric discharges leads to the growth of carbon structures on the surface of electrodes, reduces the output of the gas phase and finely dispersed carbon structures. The morphology and composition of solid phase products were determined by scanning electron microscopy and energy dispersive X-ray spectroscopy. Nanosized carbon structures are obtained in the form of aggregates - carbon nanohorns, which actively adsorb oxygen (content 0.9-3.6 at%). The composition of gaseous products was determined by gas chromatography. It was revealed that with an increase in the power of electric discharges, the hydrogen content slightly increases from 74.8 to 75.15 mol%, methane from 5.86 to 6.55 mol%, neopentane from 0.02 to 0.55 mol%. At the same time, the acetylene content in gaseous products decreases from 18.14 to 16.36 mol%.
The use of a nanostructured graphene-zirconia composite will allow the development of new materials with improved performance properties and a high functionality. This work covers a stepwise study ...related to the creation of a nanostructured composite based on ZrO2 and graphene. A composite was prepared using two suspensions: nano-zirconia obtained by sol-gel synthesis and oxygen-free graphene obtained sonochemically. The morphology of oxygen-free graphene sheets, phase composition and the morphology of a zirconia powder, and the morphology of the synthesized composite were studied. The effect of the graphene sheets on the rheological and sintering properties of a nanostructured zirconia-based composite powder has been studied. It has been found that graphene sheets in a hybrid nanostructure make it difficult to press at the elastic deformation stage, and the composite passes into the plastic region at a lower pressure than a single nano-zirconia. A sintering mechanism was proposed for a composite with a graphene content of 0.635 wt%, in which graphene is an important factor affecting the process mechanism. It has been determined that the activation energy of the composite sintering is more than two times higher than for a single nano-zirconia. Apparently, due to the van der Waals interaction, the graphene sheets partially stabilize the zirconia and prevent the disordering of the surface monolayers of its nanocrystals and premelting prior to the sintering. This leads to an increase in the activation energy of the composite sintering, and its sintering occurs, according to a mixed mechanism, in which the grain boundary diffusion predominates, in contrast to the single nano-zirconia sintering, which occurs through a viscous flow.
•The largest data set of cloud tracked winds – about 0.5 million vectors – from the VMC/Venus Express imaging.•Characterization of the mean circulation at the Venus cloud tops.•Orbit-to-orbit changes ...and diurnal variations of the mean flow.•Long-term trend: acceleration of the mean flow from 2006 to 2012.•Periodicities in the cloud top wind field.
Six years of continuous monitoring of Venus by European Space Agency’s Venus Express orbiter provides an opportunity to study dynamics of the atmosphere our neighbor planet. Venus Monitoring Camera (VMC) on-board the orbiter has acquired the longest and the most complete so far set of ultra violet images of Venus. These images enable a study the cloud level circulation by tracking motion of the cloud features. The highly elliptical polar orbit of Venus Express provides optimal conditions for observations of the Southern hemisphere at varying spatial resolution. Out of the 2300 orbits of Venus Express over which the images used in the study cover about 10 Venus years. Out of these, we tracked cloud features in images obtained in 127 orbits by a manual cloud tracking technique and by a digital correlation method in 576 orbits. Total number of wind vectors derived in this work is 45,600 for the manual tracking and 391,600 for the digital method. This allowed us to determine the mean circulation, its long-term and diurnal trends, orbit-to-orbit variations and periodicities. We also present the first results of tracking features in the VMC near-IR images. In low latitudes the mean zonal wind at cloud tops (67±2km following: Rossow, W.B., Del Genio, A.T., Eichler, T. 1990. J. Atmos. Sci. 47, 2053–2084) is about 90m/s with a maximum of about 100m/s at 40–50°S. Poleward of 50°S the average zonal wind speed decreases with latitude. The corresponding atmospheric rotation period at cloud tops has a maximum of about 5days at equator, decreases to approximately 3days in middle latitudes and stays almost constant poleward from 50°S. The mean poleward meridional wind slowly increases from zero value at the equator to about 10m/s at 50°S and then decreases to zero at the pole. The error of an individual measurement is 7.5–30m/s. Wind speeds of 70–80m/s were derived from near-IR images at low latitudes. The VMC observations indicate a long term trend for the zonal wind speed at low latitudes to increase from 85m/s in the beginning of the mission to 110m/s by the middle of 2012. VMC UV observations also showed significant short term variations of the mean flow. The velocity difference between consecutive orbits in the region of mid-latitude jet could reach 30m/s that likely indicates vacillation of the mean flow between jet-like regime and quasi-solid body rotation at mid-latitudes. Fourier analysis revealed periodicities in the zonal circulation at low latitudes. Within the equatorial region, up to 35°S, the zonal wind show an oscillation with a period of 4.1–5days (4.83days on average) that is close to the super-rotation period at the equator. The wave amplitude is 4–17m/s and decreases with latitude, a feature of the Kelvin wave. The VMC observations showed a clear diurnal signature. A minimum in the zonal speed was found close to the noon (11–14h) and maxima in the morning (8–9h) and in the evening (16–17h). The meridional component peaks in the early afternoon (13–15h) at around 50°S latitude. The minimum of the meridional component is located at low latitudes in the morning (8–11h). The horizontal divergence of the mean cloud motions associated with the diurnal pattern suggests upwelling motions in the morning at low latitudes and downwelling flow in the afternoon in the cold collar region.
Venus Express mission Svedhem, H.; Titov, D.; Taylor, F. ...
Journal of Geophysical Research - Planets,
20/May , Letnik:
114, Številka:
E5
Journal Article
Recenzirano
Odprti dostop
Venus Express is well and healthy and has now been providing exciting new data from Venus, our nearby twin planet, for over 2 years. Many of the new results are presented and discussed in the ...subsequent papers in this special section. The overall scientific objective of Venus Express is to carry out a detailed study of the atmosphere of Venus, including the interaction of the upper atmosphere with the solar wind and the interaction of the lowest part of the atmosphere with the surface of the planet. In addition, the plasma environment and magnetic fields as well as some aspects of the surface of the planet are addressed. For the first time, investigations make systematic use of the transparent infrared spectral windows in order to probe the atmosphere in four dimensions: three spatial dimensions plus time. The spacecraft design is taken from Mars Express with some modifications necessary owing to the specific environment around Venus. The payload is composed of three spectrometers, a camera, a magnetometer, an instrument for detecting energetic particles, and a radio science package. The orbit is polar and highly elliptic, with a pericenter altitude of about 200 km over the northern polar region and an apocenter altitude of 66,000 km. Presently, the coverage of the southern hemisphere is very good, but important gaps still do exist. The coverage of the northern hemisphere is much less dense. Venus Express is a part of the European Space Agency's program for the exploration of the inner solar system, which includes missions to study the Sun, Mercury, Venus, the Moon, Mars, and comets and asteroids.
Venus is completely covered by a thick cloud layer, of which the upper part is composed of sulphuric acid and some unknown aerosols. The cloud tops are in fast retrograde rotation (super-rotation), ...but the factors responsible for this super-rotation are unknown. Here we report observations of Venus with the Venus Monitoring Camera on board the Venus Express spacecraft. We investigate both global and small-scale properties of the clouds, their temporal and latitudinal variations, and derive wind velocities. The southern polar region is highly variable and can change dramatically on timescales as short as one day, perhaps arising from the injection of SO2 into the mesosphere. The convective cells in the vicinity of the subsolar point are much smaller than previously inferred, which we interpret as indicating that they are confined to the upper cloud layer, contrary to previous conclusions, but consistent with more recent study.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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