Pityusa Patera, Mars: Structural analyses suggest a mega-caldera above a magma chamber at the crust-mantle interface

Pityusa Patera is the southernmost of four paterae in the 1.2 × 106 km2 wrinkle-ridged plains-dominated Malea Planum region of Mars. Based on their texture, morphology, and uniqueness to Pityusa Patera, we interpret layered, folded massifs as pyroclastic deposits emplaced during patera formation as a collapse caldera. Such deposits would not be expected in a previously suggested scenario of patera formation by subsidence from lithospheric loading. Our structural measurements and modeling indicate that the folding and high relief of the massifs resulted from ~1.3%–6.9% of shortening, which we show to be a reasonable value for a central plug sagging down into an assumed piston-type caldera. According to a previously published axisymmetric finite-element model, the extent of shortening structures on a caldera floor relative to its total diameter is controlled by the roof depth of the collapsed magma chamber beneath it, which would imply Pityusa Patera formed above a chamber at 57.5–69 km depth. We interpret this value to indicate a magma chamber at the crust-mantle interface, which is in agreement with crust-penetrating ring fractures and mantle flows expected from the formation of the Hellas basin. As such, the folded massifs in Pityusa Patera, which are partially superposed by ca. 3.8 Ga wrinkle-ridged plains, should consist of primordial mantle material, a theory that might be assessed by future hyperspectral observations. In conclusion, we do not favor a formation by load-induced lithospheric subsidence but suggest Pityusa Patera to be one of the oldest extant volcanic landforms on Mars and one of the largest calderas in the solar system, which makes the folded, likely mantle-derived deposits on its floor a prime target for future exploration.

The Velocity Field of an Annular Jet With “Cross-Member”

An annular jet has been created by supporting a streamlined plug (dia = D1) in a delivery tube (dia = D2) with a narrow cross-member. PIV measurements have been carried out at x/D2 = 8 for four D1/D2 ratios. These observations, and the motivating criteria for this study, were used to select D1/D2 = 0.746 for detailed, near exit, velocity field measurements. Significant three-dimensional effects of the cross-member have been observed. Velocity field data, from a “sting supported, flat disk” (axisymmetric geometry) central plug provide comparative measurements. These comparisons are considered in detail.

Plastic Flow in Confined Porous Media of Complex Contours

A theoretical study of the fully developed fluid flow through a confined porous medium is presented. The fluid is described by the Bingham plastic model for small values of the yield number. The analysis allows for many admissible shapes of the wall contour. The velocity field is computed for several combination of relevant parameters, i.e., the yield number, Darcy resistance coefficient and the boundary perturbation parameter. The wall effect is especially highlighted and the characteristics of the central plug region as well. Plots of isovel curves and velocity profiles are included for a variety of flow and geometry parameters.

Evidence that vault ribonucleoprotein particles localize to the nuclear pore complex

Vaults are cytoplasmic ribonucleoprotein organelles that are highly conserved among diverse eukaryotic species. Their mass (12.9 MDa), diameter (26-35 nm) and shape (two halves, each with eightfold radial symmetry) have recently been determined and are similar to those ascribed to the central plug (or transporter) of the nuclear pore complex (NPC). The size and eightfold symmetry of the vault particle make it conducive to interacting physically in a complementary manner with NPCs. The present study demonstrates that vaults specifically associate with nuclei by both immunoblotting and immunofluorescence. Immunogold EM confirmed that vaults associate with the nuclear envelope in tissue sections and with NPCs of isolated nuclei.

Structure, assembly and interactions of the nuclear lamina and the nuclear pore complex

The nuclear pore complex (NPC) is a ∼120 MD supramolecular machine implicated in nucleocytoplasmic transport, that is embedded in the double-membraned nuclear envelope (NE). The basic framework of the ∼120 nm diameter NPC consists of a 32 MD cytoplasmic ring, a 66 MD ‘plug-spoke’ assembly, and a 21 MD nuclear ring. The ‘central plug’ seen in en face views of the NPC reveals a rather variable appearance indicating that it is a dynamic structure. Projecting from the cytoplasmic ring are 8 short, twisted filaments (Fig. 1a), whereas the nuclear ring is topped with a ‘fishtrap’ made of 8 thin filaments that join distally to form a fragile, 30-50 nm distal diameter ring centered above the NPC proper (Fig. 1b). While the cytoplasmic filaments are sensitive to proteases, they as well as the nuclear fishtraps are resistant to RNase treatment. Removal of divalent cations destabilizes the distal rings and thereby opens the fishtraps, addition causes them to reform. Protruding from the tips of the radial spokes into perinuclear space are ‘knobs’ that might represent the large lumenal domain of gp210, a membrane-spanning glycoprotein (Fig. 1c) which, in turn, may play a topogenic role in membrane folding and/or act as a membrane-anchoring site for the NPC. The lectin wheat germ agglutinin (WGA) which is known to recognize the ‘nucleoporins’, a family of glycoproteins having O-linked N-acetyl-glucosamine, is found in two locations on the NPC (Fig. 1. d-f): (i) whereas the cytoplasmic filaments appear unlabelled (Fig. 1d&e), WGA-gold labels sites between the central plug and the cytoplasmic ring (Fig. le; i.e., at a radius of 25-35 nm), and (ii) it decorates the distal ring of the nuclear fishtraps (Fig. 1, d&f; arrowheads).

Structural analysis of the nuclear pore complex and its constituents unveils a pronounced asymmetry of its cytoplasmic and nucleoplasmic faces

The nuclear pore complex (NPC) is an elaborate supramolecular organelle implicated in nucleocytoplasmic transport, enabling small molecules (diameter ≤ 9 nm) to pass freely while mediating active transport of larger molecules. By conventional transmission electron microscopy (CTEM) the NPC consists of 8 radial spokes surrounding a central channel, often appearing plugged, sandwiched between two concentric, 8-fold symmetric rings. Based on quantitative scanning trasmission EM (STEM), the intact NPC has a mass of 125 MD, the cytoplasmic ring (RC) of 32 MD, the nucleoplasmic ring (RN) of 21 MD, the plug-spoke complex (PS) of 65 MD, and the central plug (P) of 13 MD, indicating that molecularly, the NPC may easily contain 100-200 different polypeptides. Here we document the structural asymmetry of the RC and the RN by CTEM.Nuclear envelopes (NE) were manually isolated from Xenopus laevis oocytes and spread onto a carbon/colloidon-coated EM grid with the cytoplasmic side in contact. To obtain specimens comparable to those used for STEM, chemical fixation was omitted. Standard specimens were contrasted with 0.75% uranyl formate (UF) and air-dried.