Mushroom Head Research Articles

Influence of extension and compression on salt diapirism in its type area, East Carpathians Bend area, Romania

Abstract The East Carpathians Bend area has a very complex structure characterized by the presence of nappes, their post-tectonic cover and salt diapirs. The salt forming the studied diapirs is Early Miocene (Burdigalian) in age. After its accumulation the salt was more or less continuously involved in alternating extensional and compressional stages that deformed it from its original tabular position to the present-day diapir. Five stages of salt deformation have been established: initial, pre-nappe emplacement, nappe emplacement, post-nappe emplacement and Wallachian. During all of these stages the salt was configured into different shapes: it formed a truncated cone during the initial stage, a mushroom head during the prenappe emplacement stage, and an increasingly more tapered shape with nappe emplacement and during the post-nappe emplacement stages. Finally, it was squeezed out and refashioned by strike-slip faulting during the Wallachian compressional stage of Pleistocene age.

Ultrastructural observations on the male gametes in Austrognathia sp. (Gnathostomulida, Bursovaginoidea).

The male gametes of the gnathostomulid bursovaginoid Austrognathia sp. were investigated by electron microscopy. All stages of sperm development can be observed in the single saccular male gonad, which is enclosed by a relatively thick basement membrane internally reinforced by thin smooth muscle cells. The spermatogonia are situated close to the testicular theca and produce generally separate primary spermatocytes. From secondary spermatocytes onwards, the nuclear envelope is no longer visible. The spermatids develop synchronously in groups of four, in contrast to arthropod and vertebrate spermatogenesis. A single, large nurse cell, or trophocyte, never observed previously, surrounds each spermatid; perhaps it represents an altered germ cell functioning in nutrition. The spermatid nucleus, initially ovoid, lengthens and takes on the shape of a mushroom head extending into a stalk. Three degrees of chromatin condensation are visible. Anteriorly, a palisade-shaped structure is present just over the highly heterochromatic nuclear zone and is considered to have an acrosome-like function. The outer sperm cytoplasm is characterized by a peripheral tubular labyrinth. Axonemal structures have never been found, but centriole-like structures are present among the medium-density chromatinic strands of the mushroom-like nucleus. No cortical microtubules are evident beneath the cell membrane. The external sperm morphology recalls that of nematode gametes, and some internal features are also similar. Phylogenetic considerations and hypotheses on sperm locomotion are proposed. J. Morphol. 237:165-176, 1998. © 1998 Wiley-Liss, Inc.

Impact damage of laminated composite with energy dissipation: Part I — Nonhomogenous characteristics

Composite laminates could be made to diffuse penetration energy at predetermined rates in addition to locations. Materials with different hardness and toughness can be stacked in the appropriate sequence to create a more widespread damage pattern. The kinetic energy per unit volume of the laminate could then be reduced to prevent complete perforation. Analyzed in detail is the failure sequence of a tungsten rod (47 mm long and 14 mm in diameter) impacting a three-layered composite laminate at 1100 m/s. The top layer is a 6 mm thick ceramic (Al 2O 3). Sandwiched in between is a 10 mm thick rubber layer backed up by a 4 mm thick 4340 steel plate. At approximately 10 μs, the tungsten rod is already badly shattered, whereas the ceramic is only fragmented in a layer next to the surface. The ceramic reflects the impact waves which cause damage in the tungsten rod. Within the next 1.50 μs, i.e. 21.5 μs, the dissipated energy density in the rubber increased two orders of magnitude from 32.11 to 33.25 × 10 2 Pa while those in the ceramic and steel are much smaller. The highest temperature in the ceramic reached about 555°C and that in the back-up steel plate is only 275°C. Upon complete fragmentation of the tungsten rod, a through the thickness cavity is predicted in the ceramic while a mushroom head shaped crack is predicted in the rubber. Interfacial cracks are widespread but the steel layer remained intact. Presentation is divided into two parts. Part I describes the basic scheme of the methodology and the nonhomogeneous character of response within each layer of the composite laminate. That is the constitutive relation for each material element is derived according to the local strain and strain rate rather than preassumed. Thermal/mechanical interactions are synchronized by application of the isoenergy density theory in nonequilibrium thermomechanics. At 0.15 μs, concentration of energy is detected at the impact site and ceramic/rubber interface. The finite element grid pattern had to be remeshed after 50 μs to account for the discontinuities created by damage at the interphases. Modelled in Part 11 are the evolution of damage in steps until the tungsten rod is completely destroyed. Nonequilibrium data such as load strain rates, temperatures, dissipation energies, etc. are given numerically and displayed graphically.

A Low Cost Synthesis Technique for Tungsten Whiskers of <100> Orientation

Abstract Despite numerous advancements in WHA technology, DU penetrators consistently outperform WHA penetrators in ballistic tests. The poor performance of WHA penetrators is related to its mushroom head which forms during the penetration process thereby decreasing the energy density at the target. In contrast, DU penetrators localize deformation thereby maintaining a chisel nose during the penetration process. W single crystals of (100) orientation have been demonstrated to perform at least as well as DU penetrators; this is attributable to the favorable slip/cleavage during compressive loading without large scale plastic deformation and the occurrence of shear localization at a favorable angle for easy material flow away from the penetrator interface. Unfortunately, the brittleness of W single crystals coupled with the exorbitant cost associated with procurement of large diameter single crystals implies that novel low cost approaches are necessary to improve the penetration performance of WHA penetrato...

South Atlantic hot spot-plume systems: 1. Distribution of volcanism in time and space

New Ar—Ar dating of rocks dredged from seamounts and ridges distributed along the St. Helena and Gough volcanic chains suggests that these features were formed by, respectively, the activity of the St. Helena and Walvis hot spot-plume systems. The St. Helena and Walvis (referred to elsewhere as Tristan) hot spots probably consist of broad zones of diffuse volcanism (i.e. oceanic islands, seamounts, and small ridges), at least 500 km in diameter. It remains unclear as to whether one or several narrow plume(s) is (are) upwelling to form these broad zones of hot spot volcanism, which results from decompression melting across parts of the broad, impacted ‘mushroom head’ of the plume(s). The very slow velocity of the African plate, in association with the westward flow of St. Helena and Walvis plume material to the South Atlantic spreading-axis, are likely to be important factors in the development of these broad fields of mid-plate volcanism. On a more localized scale, lithospheric structure (e.g. fracture zones) probably controls the locations of sites of hot spot volcanism. The distributions of Ar—Ar ages along the St. Helena and Gough chains, in conjunction with the proposition of their having been formed by broad hot spots, have been incorporated into a reconstruction of African plate motion over hot spot-plume systems since the opening of the South Atlantic. Estimates of the velocity of the African plate suggest that the African plate might have slowed significantly between ∼ 31 and 0 Ma. The South Atlantic spreading axis migrated westward away from the (fixed?) St. Helena and Walvis hot spot-plume systems, this migration beginning between ∼ 80 and 70 Ma. This led to a transition from an on-spreading-axis to a mid-plate constructional setting along the St. Helena Chain and the Walvis Ridge.

Mushrooms as biological monitors of trace elements in the environment

Mushrooms as a functional system relating to the most important environmental compartments (soil, water, air), may be used advantageously as biological monitors of the state of the environment. In particular the aerial parts of the mushroom (head and stem), because of their rapid growth rate from a few days to a few weeks, could be a useful indicator of fluctuations that may occur in the ecosystem. In this study the levels of fallout radionuclides134Cs,137Cs, due mostly to the Chernobyl nuclear accident, of natural radionuclide40K and of the stable elements Se, Hg, Cr, Cs, Sc, Rb, Zn, Fe, Co, Eu, Sb, Ag, Ce, Ba, Ni present in the head and stem of mushroom samples from an area of the Italian Alps were measured. The analytical technique used was Instrumental Neutron Activation Analysis and gamma-spectrometry. The results are discussed and possible correlations with other environmental parameters are examined.

An analytical model on penetration of eroding long rods into metallic targets

We developed an analytical model to predict the performance of eroding long rods that penetrated metallic targets at normal incidence with impact velocities above 2.0 km/s. The model predicted cavity diameter, penetration depth and penetration velocity as functions of projectile velocity. Post-test observations and dynamic, in-material X-ray photographs guided the development of the model. The flash X-ray photographs indicated that the nose of a projectile mushroomed upon penetrating into a target, and then the mushroom head maintained its diameter and nearly hemispherical shape throughout the primary quasi-steady penetration stage. This observation suggested that we could use the results of spherical cavity-expansion analysis on non-deforming projectiles to calculate target resistance against the penetration of eroding rods. To verify the model, we conducted terminal-ballistic experiments with 4340 steel rods penetrating into 6061-T651 aluminum targets and Teledyne X21-C tungsten rods penetrating into 4340 steel targets at impact velocities between 2.0 and 3.1 km/s. The model predictions were in good agreement with the data.

Faceted contact lens with a modified viewing device for fundus examination.

Anterior fundus examination with a gonioscope through a flat surface on a contact lens is of comparatively recent date.1It has been used for viewing the fundus as far forward as the ora serrata and pars plana, using either simple scleral depression or a transillumination technique.2It provides greater magnification of the extreme fundus periphery than can be obtained with ordinary indirect ophthalmoscopy. Experience with this method aided the designing of diagnostic contact lens and a completely mobile slit lamp-gonioscope. Contact Lenses An oblique plano surface on a contact lens for anterior fundus examination can be obtained by oblique section of a cylindrical plexiglass lens.1The same is achieved by cutting an oblique slice from the mushroom head of the Troncoso type lens (plano facet) (Fig la, b). Another way of achieving the same effect is to fit the convex surface of the Troncoso lens with