Proteins to be secreted are transported from the endoplasmic reticulum (ER) to the Golgi apparatus. The transport of these proteins requires the localization and activity of proteins that create ER ...exit sites, coat proteins to collect cargo and to reshape the membrane into a transport container, and address labels--SNARE proteins--to target the vesicles specifically to the Golgi apparatus. In addition some proteins may need export chaperones or export receptors to enable their exit into transport vesicles. ER export factors, SNAREs, and misfolded Golgi-resident proteins must all be retrieved from the Golgi to the ER again. This retrieval is also part of the organellar homeostasis pathway essential to maintaining the identity of the ER and of the Golgi apparatus. In this review, I will discuss the different processes in retrograde transport from the Golgi to the ER and highlight the mechanistic insights we have obtained in the last couple of years.
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Vesicular transport is the basic communication mechanism between different compartments in a cell and with the environment. In this review I discuss the principles of vesicle generation and ...consumption with particular emphasis on the different types of coat proteins and the timing of the shedding of the coat proteins from transport containers. In recent years it has become clear that there are more coat complexes than the classical COPI, COPII and clathrin coats. These additional coats may generate vesicles that transport cargo in a temporally and/or spatially controlled manner. Work over the last years suggests that GTP hydrolysis occurs early during vesicle biogenesis, destabilizing the coat perhaps before fission of the vesicle from the donor membrane occurs. Recent findings imply, however, that tethers at the receiving compartment specifically detect the coat on vesicle. (Part of a Multi-author Review)
Vesicular transport is the basic communication mechanism between different compartments in a cell and with the environment. In this review I discuss the principles of vesicle generation and ...consumption with particular emphasis on the different types of coat proteins and the timing of the shedding of the coat proteins from transport containers. In recent years it has become clear that there are more coat complexes than the classical COPI, COPII and clathrin coats. These additional coats may generate vesicles that transport cargo in a temporally and/or spatially controlled manner. Work over the last years suggests that GTP hydrolysis occurs early during vesicle biogenesis, destabilizing the coat perhaps before fission of the vesicle from the donor membrane occurs. Recent findings imply, however, that tethers at the receiving compartment specifically detect the coat on vesicle.
The Emergence of Life Camprubí, E.; de Leeuw, J. W.; House, C. H. ...
Space science reviews,
12/2019, Volume:
215, Issue:
8
Journal Article
Peer reviewed
Open access
The aim of this article is to provide the reader with an overview of the different possible scenarios for the emergence of life, to critically assess them and, according to the conclusions we reach, ...to analyze whether similar processes could have been conducive to independent origins of life on the several icy moons of the Solar System. Instead of directly proposing a concrete and unequivocal cradle of life on Earth, we focus on describing the different requirements that are arguably needed for the transition between non-life to life. We approach this topic from geological, biological, and chemical perspectives with the aim of providing answers in an integrative manner. We reflect upon the most prominent origins hypotheses and assess whether they match the aforementioned abiogenic requirements. Based on the conclusions extracted, we address whether the conditions for abiogenesis are/were met in any of the oceanic icy moons.
Geodynamic Modeling With Uncertain Initial Geometries Spang, A.; Baumann, T. S.; Kaus, B. J. P.
Geochemistry, geophysics, geosystems : G3,
June 2022, 2022-06-00, 20220601, 2022-06-01, Volume:
23, Issue:
6
Journal Article
Peer reviewed
Open access
Geodynamic codes have become fast and efficient enough to facilitate sensitivity analysis of rheological parameters. With sufficient data, they can even be inverted for. Yet, the geodynamic inverse ...problem is often regularized by assuming a constant geometry of the geological setting (e.g., shape, location and size of salt diapirs or magma bodies) or approximating irregular bodies with simple shapes like boxes, spheres or ellipsoids to reduce the parameter space. Here, we present a simple and intuitive method to parameterize complex 3D bodies and incorporate them into geodynamic inverse problems. The approach can automatically create an entire ensemble of initial geometries, enabling us to account for uncertainties in imaging data. Furthermore, it allows us to investigate the sensitivity of the model results to geometrical properties and facilitates inverting for them. We demonstrate the method with two examples. A salt diapir in an extending regime and free subduction of an oceanic plate under a continent. In both cases, small differences in the model's initial geometry lead to vastly different results. Be it the formation of faults or the velocity of plates. Using the salt diapir example, we demonstrate that, given an additional geophysical observation, we are able to invert for uncertain geometric properties. This highlights that geodynamic studies should investigate the sensitivity of their models to the initial geometry and include it in their inversion framework. We make our method available as part of the open‐source software geomIO.
Plain Language Summary
Computer models of geological settings have become a popular tool of research. They require the user to provide information on where the different geological units (rock layers, salt domes, magma bodies etc.) start and end as well as material parameters like density and strength of the units. As many of these input parameters are not well known, a lot of studies perform multiple simulations with different parameter combinations to investigate the influence the individual parameters and their uncertainties have. However, the initial geometry often remains fixed as it is difficult to describe with only few parameters and therefore unrealistic to vary. Here, we present a new method to describe and manipulate the geometry of geological units with a small number of parameters. This allows us to also vary the initial geometry and investigate how the model results depend on it. We apply our method to a salt diapir and a subduction zone to demonstrate the impact of initial geometry on the simulation results. To make our method available to the community, we implement it as a tool into geomIO, an open‐source software package to generate initial geometries for geodynamic models.
Key Points
New, simple, intuitive and open‐source method to describe and manipulate complex 3D bodies with a small number of parameters
Allows for the integration of uncertainties of the initial geometry and enables inverting for geometric properties in numerical models
Applications to a salt diapir with uncertain initial geometry and a subduction zone with uncertain initial subduction angle
ABSTRACT The creation of a dark hole (DH) region in the science image for exoplanet direct detection depends on deformable mirrors (DMs), where the imperfect control of DM limits the achievable ...contrast. The mirror surface height resolution is set by the DM drive electronics, and the quantization errors in DM impact the contrast in the DH. Consequently, determining the optimal voltage value for the flattening map of DM is essential, as it involves balancing dynamic and accuracy considerations. We conduct a numerical study to examine the impact of these parameters on microelectromechanical DM within the high-contrast field of view of several DHs with various characteristics and optical configurations. Our analysis includes an exploration of their influence on both small and moderate angular separations. We compare our numerical results with a formula available in the literature that aims to capture the dependence of contrast on DM quantization errors. We show that the formula accuracy to predict the contrast limit when the DM deflection curves follow the as-manufactured quadratic power law is dependent on the DM flattening map voltage domain, regardless of DH size and angular separations. Further these results appear to be insensitive to factors such as actuator number, coronagraph type, set-up architecture, and science objective (small or moderate angular separations). We provide guidelines for determining the optimal voltage for the DM flattening map, discuss the domain validity of the formula used to predict DM quantization errors on the contrast, and provide insights into balancing DM actuator density and mirror surface height resolution.
Crustal‐stored magma reservoirs contain exsolved volatiles which accumulate in the reservoir roof, exerting a buoyancy force on the crust. This produces surface uplift and sudden loss of volatiles ...through eruption results in syn‐eruptive subsidence. Here, we present three‐dimensional, visco‐elasto‐plastic, numerical modeling results which quantify the ground deformation arising from the growth and release of a volatile reservoir. Deformation is mostly independent of crustal thermal distribution and volatile reservoir shape, but is a function of volatile volume, density and depth and crustal rigidity. We present a scaling law for the volatiles' contribution to syn‐eruptive subsidence and show this contributes ∼20% of the observed subsidence associated with the 2015 Calbuco eruption. Our results highlight the key role that volatile‐driven buoyancy can have in volcano deformation, show a new link between syn‐eruptive degassing and deflation, and highlight that shallow volatile accumulation and release may have a significant impact on ground deformation of volcanoes.
Plain Language Summary
Magma contains a lot of gases which separate from it when it approaches the surface. These gases can collect right above the magma storage region a few kilometers below the surface. They have a much lower density than the rocks surrounding them and push upwards like a balloon filled with air that is pressed under water. In this study, we use computer models to understand how much a volcano would grow from the push of the gases below and how much it would shrink when the gases escape because of an eruption. We find that the gases can cause the volcano to grow and shrink up to a few centimeters during accumulation and release, respectively. The amount of surface movement depends on the volume, density and depth of the gas reservoir as well as on the toughness of the rocks above it. We derive a simple equation which allows us to compute the surface movement using the aforementioned parameters. With this equation and estimates about the amount of accumulated gas at the 2015 Calbuco eruption, we can assume that about 20% of the observed surface movement was caused by the release of the magmatic gases.
Key Points
Exsolving volatiles accumulate at the roof of a magma storage zone and contribute to surface deformation through buoyancy forces
3D numerical models show that surface deformation is a function of the volatiles' volume, density and depth as well as crustal rigidity
Volatile release during eruption can cause syn‐eruptive subsidence of a few cm, which is 20% of the observed signal at Calbuco in 2015
Aims. V838 Monocerotis erupted in 2002, brightened in a series of outbursts, and eventually developed a spectacular light echo. A very red star emerged a few months after the outburst. The whole ...event has been interpreted as the result of a merger. Methods. We obtained near- and mid-IR interferometric observations of V838 Mon with the AMBER and MIDI recombiners located at the Very Large Telescope Interferometer (VLTI) array. The MIDI two-beam observations were obtained with the 8 m unit telescopes between October 2011 and February 2012. The AMBER three-beam observations were obtained with the compact array (B ≤ 35 m) in April 2013 and the long array (B ≤ 140 m) in May 2014, using the 1.8 m auxiliary telescopes. Results. A significant new result is the detection of a compact structure around V838 Mon, as seen from MIDI data. The extension of the structure increases from a FWHM of 25 mas at 8 μm to 70 mas at 13 μm. At the adopted distance of D = 6.1 ± 0.6 kpc, the dust is distributed from about 150 to 400 AU around V838 Mon. The MIDI visibilities reveal a flattened structure whose aspect ratio increases with wavelength. The major axis is roughly oriented around a position angle of − 10°, which aligns with previous polarimetric studies reported in the literature. This flattening can be interpreted as a relic of the 2002 eruption or as caused by the influence of the currently embedded B3V companion. The AMBER data provide a new diameter for the pseudo-photosphere, which shows that its diameter has decreased by about 40% in 10 yr, reaching a radius R∗ = 750 ± 200 R⊙ (3.5 ± 1.0 AU). Conclusions. After the 2002 eruption, which was interpreted as the merging of two stars, it seems that the resulting source is relaxing to a normal state. The nearby environment exhibits an equatorial overdensity of dust up to several hundred AU.
Context. It has been shown that convection in red supergiant stars (RSG) gives rise to large granules that cause surface inhomogeneities and shock waves in the photosphere. The resulting motion of ...the photocentre (on time scales ranging from months to years) could possibly have adverse effects on the parallax determination with Gaia. Aims. We explore the impact of the granulation on the photocentric and photometric variability. We quantify these effects in order to better characterise the error that could possibly alter the parallax. Methods. We use 3D radiative-hydrodynamics (RHD) simulations of convection with CO5BOLD and the post-processing radiative transfer code Optim3D to compute intensity maps and spectra in the Gaia G band 325-1030 nm. Results. We provide astrometric and photometric predictions from 3D simulations of RSGs that are used to evaluate the possible degradation of the astrometric parameters of evolved stars derived by Gaia. We show in particular from RHD simulations that a supergiant like Betelgeuse exhibits a photocentric noise characterised by a standard deviation of the order of 0.1 AU. The number of bright giant and supergiant stars whose Gaia parallaxes will be altered by the photocentric noise ranges from a few tens to several thousands, depending on the poorly known relation between the size of the convective cells and the atmospheric pressure scale height of supergiants, and to a lower extent, on the adopted prescription for galactic extinction. In the worst situation, the degradation of the astrometric fit caused by this photocentric noise will be noticeable up to about 5 kpc for the brightest supergiants. Moreover, parallaxes of Betelgeuse-like supergiants are affected by an error of the order of a few percents. We also show that the photocentric noise, as predicted by the 3D simulation, does account for a substantial part of the supplementary "cosmic noise" that affects Hipparcos measurements of Betelgeuse and Antares.
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