Axial Regions Research Articles

Okinawa Trough: Origin of a back-arc basin

The sequence of back-arc basin development in the southwestern part of Okinawa Trough has apparently been crustal thinning, involving normal faulting and fault block rotation, rifting, and crustal separation with associated magmatic intrusion. Seismic-refraction data shows a mantle depth of about 15 km beneath the central rift of Okinawa Trough while gravity data suggests that the crust thickens away from the central region of Okinawa Trough towards both the Ryukyu Arc and the continental shelf. Seismic-reflection profiles across Okinawa Trough reveal a generally continuous, undisturbed upper sediment section beneath the trough floor, unconformably overlying a highly faulted lower section which has a velocity of 4.9 km/sec. Exceptions to this structural relationship are fault grabens cutting the upper section along the axial and southeastern regions of the trough and normal faults at the extreme margins of the trough. Correlation of similar structural relationships on Taiwan suggests that extension produced normal faults in the lower section during Miocene time creating the initial expression of Okinawa Trough, and that the unconformity between the upper and lower sections is of Miocene age. Linear magnetic anomalies and high-velocity crustal rocks associated with the central trough region are interpreted as due to Pliocene to Recent magmatic intrusion associated with crustal separation. Offsets in the magnetic lineations indicate that the crust is separating along a series of short spreading centers and transform offsets.

Mechanics of a porous two-phase strongly viscous medium and some geophysical applications

According to modern geophysical ideas [1], the oceanic crust is formed when the lithospheric plates move apart in the axial regions of the rift zones of the Earth due to the penetration of molten matter from the asthenosphere into cracks and pores of the lithosphere and the subsequent solidification of this matter (the lithosphere and asthenosphere are the upper layers of the Earth). In these regions, which have a width of the order of several tens of kilometers, the liquid magmatic material penetrates the crystalline skeleton of the crust, which means that one must regard this region as a saturated fissured and porous deformable medium that permits phase transitions between the skeleton and the liquid filler. Geophysical data indicate that there is a similar two-phase fissured and porous structure of the medium in the asthenosphere (at least in certain regions) and in regions of high tectonic and volcanic activity. Because geological processes take place slowly, it can be assumed that the skeleton of the two-phase medium is deformed as a strongly viscous incompressible Newtonian liquid with a viscosity much greater than the viscosity of the filler.

Heterogeneous nuclear RNA (HnRNA) size in developing frog embryos

Different stages of developing frog embryos were briefly labeled with [ 3H]uridine and the rapidly labeled RNA was denatured and sized by sucrose density gradient centrifugation. Studies of the accumulation of labeled nuclear and cytoplasmic RNA were employed to learn the extent of turnover of nuclear RNA. Heterogeneous nuclear RNA (HnRNA) size increases during development and this is correlated with an increasing degree of turnover of HnRNA. Size differences of HnRNA exist between axial and belly regions of tailbud embryos. These data suggest that the differences in sizes of nuclear RNA may be important for post-transcriptional processing of HnRNA and control of gene expression in developing frog embryos.

Geophysical, petrological and geochemical models of the oceanic lithosphere

Available data on the thermal, geochemical and petrological properties and the seismic structure of the oceanic lithosphere are reviewed. Processes taking place in the axial regions of spreading ridges, where the lithosphere is formed are discussed. Models of the lithosphere are examined in the light of this information.

Design considerations for a shallow-well mirror experiment

The design of a “shallow-well” mirror device suitable for production and confinement of an electron cyclotron heated plasma is described. The well is shallow in that the radial variation of the magnetic field strength is ∼ 5%, with a 2:1 axial mirror ratio. The design uses elliptical mirror coils, circular central coils, and straight, skewed quadrupole coils. Coil positions and currents are optimized by finding those combinations which result in the largest axial and radial regions of favourable particle drift. The particle drift direction is determined from the radial gradient of the longitudinal invariant J. The limits on adiabaticity are estimated from the magnetic field gradients. These considerations show that a plasma would be confined with an axial extent of ∼ 160 cm. a radial extent of ∼ 20 cm, and with an adiabatic limit to the electron energy in excess of 5 MeV.

Replicon growth rates during DNA replication in developing frog embryos

The rate of replicon growth during DNA replication was determined for unsynchronized and partially synchronized explants of developing frog embryos ( Rana pipiens). The replicon growth rates for unsynchronized gastrulae, neurulae and tailbuds are 0.06, 0.08 and 0.10 μm/min, respectively. In partially synchronized embryos the replicon growth rates during the early and late S phase are 0.10 and 0.02 μm/min in neurulae and 0.11 and 0.09 μm/min in tailbud embryos, respectively. There were no differences in growth rate between the dorsal axial and belly regions of neurulae and tailbuds. From these results the size and number of replicons was calculated.

Ultrastructure and composition of the synaptonemal complex in spread and negatively stained spermatocytes of the golden hamster and the albino rat.

The ultrastructure of the synaptonemal complex (SC) has been studied in spermatocytes of the golden hamster and the albino rat, spread on liquid surfaces and negatively stained with uranyl acetate. The conditions for a reproducible procedure for spreading the SC have been specified. Spreading on water causes large losses of material from the complex. Spreading on 0.45–0.9% NaCl in water results in good preservation of the SC. Ethanol dehydration introduces irreversible changes in the shape of the chromatin fibers and the components of the complex. Digestions with DNase and proteases, extraction with 2M NaCl and fixation in an aqueous solution of formaldehyde permit analysis of the components of the SC. The lateral elements of the SC are formed by three components: 1) the bulk material which is protease sensitive, DNase resistant, insoluble in 2M NaCl and partially soluble in water; 2) the axial attachment regions of the chromatin fiber; and 3) an axial and linear filament, 65 A wide, which is DNase sensitive. It is suggested that this linear 65 A filament contains a single linear DNA molecule to which the chromatin fibers are attached. The central element of the SC is made of fibrillar material, most of which is DNase resistant and protease sensitive. Fibrils 25 A wide cross the central space and merge with the central element. The cross fibrils and the central element are labile in solutions containing less than 0.45% NaCl. — From the present results and previous data on diplotene axes (Solari, 1970), it is concluded that the lateral elements of the SC of hamster and rat spermatocytes are undivided during pachytene. It is suggested that the singleness of the axes in the lateral elements is based on the presence of a single DNA molecule axially located in the lateral elements, and that the chromatin fibers are symmetrically attached to this DNA molecule.

The time of DNA replication in the cell cycle in relation to RNA synthesis in frog embryos.

AbstractVariations in the rates of DNA and RNA synthesis during the DNA synthetic (S) period of the cell cycle have been determined in explants of early Rana pipiens embryos.Cells of dorsal axial ectoderm‐mesoderm regions and belly endoderm regions of the embryo were partially synchronized using 5‐fluorodeoxyuridine. The partially synchronized explants were incubated continuously or at intervals during the S period with radioactive nucleic acid precursors. Autoradiographic and biochemical evidence indicates that at the gastrula, neurula and tailbud stages the DNA is replicated discontinuously in two maxima with a slowing in the synthetic rate in the middle of the S period. There is an increase in the proportion of the DNA which replicates late as development proceeds from gastrulation. At the neurula and tailbud stages the proportion of late replicating DNA is greater in the belly endoderm than in the dorsal axial ectoderm‐mesoderm.Experiments utilizing H3‐5‐uridine indicate that RNA is synthesized discontinuously in two maxima during the S period in both dorsal axial and belly regions at the earlier neurula stage. By the tailbud stage, however, a significant decrease in the second maximum of RNA transcription occurs. RNA extraction experiments indicate that these changes can be attributed, in part, to changes in the synthesis of DNA‐like RNA. These findings are discussed in relation to cell determination.

Effect of actinomycin D on early axial development in chick embryos.

AbstractA study was made of the uptake of actinomycin D, 3H‐thymidine, and 3H‐uridine in the axial regions of 11‐ to 13‐somite chick embryos cultured in vitro. Actinomycin D was taken up into all regions of embryos, with significantly more actinomycin D per cell in the axial region, including the node and unsegmented axial mesoderm (the lower axis). Demonstrable effects on RNA synthesis were restricted to tissue in the lower axial region. However, inhibition of DNA synthesis was seen in tissues of the upper axis already segmented, as well as in the lower axis. The differential response of the embryonic axis to actinomycin D is considered to be based on a greater demand for cells in the unsegmented and nodal region. Actinomycin D inhibited RNA synthesis, thereby inhibited DNA synthesis and cell division, and reduced availability of cells for growth and development. The paucity of cells in the node and unsegmented axial mesoderm restricted the formation of new somites and the laying down of new nerve cord and notochordal tissue. The upper axial region was not permanently affected.

Oolites and deformation

SummaryA study in the deformational patterns of oolites from the Krol Series of the Simla Himalayas has been made in the type area. The deformation in the oolites is the result of the tectonic phenomenon coupled with folding movements during the Himalayan orogeny. The deformation varies with the amount and type of the matrix surrounding the oolites. The angle between the long axis of the ellipse and the principal tectonic extension is smallest in the axial regions of the folds.

Investigations into sulfide mineralization at Mount Isa, Queensland [discussion

With reference to a paper by Solomon (for reference, see this Bibliography Vol. 30), it is pointed out that it is not necessary to invoke the same processes to explain both the coarseness of sulfides in regions of plastic deformation (axial regions of folds) and the exsolution of chalcopyrite from the sphalerite of veins. High pressure alone would tend to retard recrystallization, whereas deformation would tend to activate it. Fracture fillings occur in both deformed and undeformed rocks, so their coarse grain and chalcopyrite exsolution probably have nothing to do with deformation.

An Adiabatic Model for Space-Dependent Boiling Water Reactor Kinetics

This and the companion paper(1) deal with space-dependent boiling water reactor kinetics by the method of adiabatic approximation. In this paper, equations are derived for axially space-dependent BWR feedback kinetics. These equations are coupled to the neutron equations through adiabatic approximation. The reactor is divided into a number of axial regions. Assuming a trapezoidal distribution of the void and the water velocity distributions along the axis, balance equations for energy and mass are integrated to yield the region-exit quantities. With other pertinent equations, a computer code is written. Some numerical results for a sample BWR are presented in the companion paper.

APPEARANCE AND LOCALIZATION OF A NERVE GROWTH-PROMOTING PROTEIN DURING DEVELOPMENT

A nerve growth-promoting protein (NGF) has been identified in a number of vertebrate species, including the human fetus. This protein can be localized to the axial regions or the sympathetic chain directly, and wherever found is immunologically similar to NGF from mouse salivary gland. During development NGF appears concomitant with morphologic differentiation of the sympathetic chain and always in association with it. These studies further implicate the participation of the nerve growth-promoting protein in the regulation of growth of sympathetic ganglia.

FUNCTIONAL EVIDENCE FOR THE EXISTENCE OF A THIRD CELL TYPE IN THE RENAL GLOMERULUS

TWO TYPES OF CELLS CAN BE RECOGNIZED ON THE LUMINAL SIDE OF THE GLOMERULAR BASEMENT MEMBRANE: the superficial endothelial cells which directly line the lumen and are comparable to endothelia lining the capillaries of other tissues, and the deep cells, ordinarily not in contact with the lumen, which are distinguished by their long cytoplasmic arms extending for some distance in several directions along the capillary wall, numerous spinous processes, and occasional intraluminal pseudopodia. Experiments carried out with electron-opaque tracers indicated that a functional distinction, based on extent of phagocytosis, can be made between the superficial and deep cells, thus supporting the existence of a distinctive "third" cell (in addition to endothelium and epithelium) in the renal glomerulus. Ferritin, colloidal gold, or thorotrast was administered intravenously to normal and, in the case of ferritin, to nephrotic rats. Kidney tissue was fixed at selected intervals from 1 hour to 10 days after the injection and studied by electron microscopy. Within 1 to 4 hours after tracer administration, the particles which did not traverse the glomerular capillary wall gradually accumulated in the less compact, inner strata of the basement membrane and the large spongy areas of axial regions. After 1 day the concentration of circulating tracer declined and the peripheral areas of the capillaries became relatively free of particles while large accumulations developed in the axial regions. During this period increasing quantities of ferritin were taken up by the deep cells and were found within large and small sized invaginations of their cell membrane or concentrated within cytoplasmic vesicles, vacuoles, multivesicular and dense bodies. At the same time the deep cells showed increased numbers of intraluminal pseudopodia. Within 2 to 4 days the deposits in the spongy areas were cleared and concomitantly increased quantities of tracer appeared in the deep cells within dense cytoplasmic bodies, some of which were more compact than before. When ferritin was given to nephrotic animals the sequence of events was generally the same except that the ferritin deposits at any given period were more massive, their incorporation into the deep cells occurred primarily by means of large pockets 1 to 2 micro in diameter and their clearance from the spongy areas was slower. In normal as well as in nephrotic animals, the phagocytic activity of the superficial endothelium was negligible when compared to that of the deep cells.

Glomerular permeability. II. Ferritin transfer across the glomerular capillary wall in nephrotic rats.

Ferritin was used as a tracer to investigate glomerular permeability in the nephrotic rat. The results were compared with those previously obtained in normal animals. A nephrotic syndrome was induced by 9 daily injections of the aminonucleoside of puromycin. Ferritin was administered intravenously on the 10th day, and kidney tissue was fixed at intervals of 5 minutes to 44 hours after injection of the tracer and examined by electron microscopy. The observations confirmed that at this stage of the experimental nephrotic syndrome the changes affect predominantly the visceral epithelium (loss of foot processes, reduction and modification of urinary slits, and intracellular accumulation of vacuoles and protein absorption droplets). Less extensive changes were found in other layers (reduction of endothelial fenestrae, an increase in the population of "deep" cells, and a thinning and "loosening" of the basement membrane.) At short intervals (5 to 15 minutes) after ferritin administration, the tracer was found at high concentration in the lumen and endothelial fenestrae, and at decreasing concentrations embedded throughout the basement membrane and incorporated into the epithelium (within cytoplasmic vesicles and within invaginations of the plasmalemma facing the basement membrane). After longer intervals (1 to 3 hours) the distribution of the tracer within the capillary wall was similar except that its concentration in the epithelium was higher, and, in addition to plasma membrane invaginations and small vesicles, ferritin also marked larger vacuoles, dense bodies, and intermediate forms. Large accumulations of tracer typically occurred in the spongy areas of the basement membrane, especially in the axial regions. Ferritin also appeared in the endothelium within membrane-limited vacuoles and dense bodies, particularly in the deep cells. After 6 to 44 hours the tracer still occurred in the lumen and throughout the basement membrane. The ferritin deposits in the spongy areas as well as the ferritin-containing vacuoles of the deep endothelium were larger and more numerous. In the epithelium ferritin was found not only within various membrane-limited bodies, but also "free" within the cytoplasmic matrix. These observations indicate that in the nephrotic glomerulus, as in the normal, the basement membrane functions as the main filtration barrier; however, in nephrosis, the basement membrane is defective and allows leakage of increased quantitites of ferritin and presumably plasma proteins. The basement membrane defect appears to be fine and widespread, occurring at or near the molecular level of organization of the filter. The accumulation of unfiltered ferritin in axial regions together with the demonstration of its subsequent phagocytosis by the "deep" endothelial cells suggest that the latter may function in the removal of filtration residues. Finally, the findings indicate that in the nephrotic, as in the normal animal, the epithelium acts as a monitor that recovers, at least in part, the protein which leaks through the filter, and that in nephrosis, the recovering activities of the epithelium are greatly enhanced because of the increased permeability of the basement membrane.

GLOMERULAR PERMEABILITY

Ferritin was used as a tracer to investigate pathways and mechanisms for transfer across the various layers of the glomerular capillary wall. Kidney tissue, fixed at intervals of 2 minutes to 2 hours following an intravenous injection of ferritin, was examined by electron microscopy. The observations confirmed the existence of three distinct and successive layers in the glomerular capillary wall (the endothelium, the basement membrane, and the visceral epithelium). In addition, they demonstrated a number of new structural features: namely (a) discrete fibrils in the subendothelial spaces; (b) a characteristic, highly elaborate, cytoplasmic organization in the visceral epithelium; and (c) special structures resembling "desmosomes" in the slits between foot processes. In animals sacrificed at short time intervals (2 to 15 minutes) following ferritin administration, ferritin molecules were found at high concentration in the lumen and endothelial fenestrae, at low concentration in the basement membrane, and in very small numbers within the epithelium. Later (1 to 2 hours), the tracer particles were still present in the lumen and within endothelial fenestrae, and, in addition, had accumulated on the luminal side of the basement membrane, especially in the axial regions of the vessels. Larger numbers of ferritin molecules were also found in the epithelium-in invaginations of the cell membrane at the base of the foot processes, and in various membrane-limited bodies (vesicles, multivesicular bodies, vacuoles, and dense bodies) present within the cytoplasm. These observations suggest that the endothelial fenestrae are patent and that the basement membrane is the main filtration barrier. Since the basement membrane has no demonstrable pores, it is probably not a simple sieve but presumably is a gel-like structure with two fine fibrillar components embedded in an amorphous matrix. Both the epithelium and endothelium may be concerned with building and maintaining this structure. Finally, the intracellular accumulation of particles in the epithelium suggests that the latter acts as a monitor that recovers, at least in part, the small amounts of protein which normally leak through the filter.

The Namurian of the Lancaster Fells

Summary The Lancaster Fells are situated in the northern part of the Central Province and the Namurian sequence resembles that of the similarly placed Rombalds Moor region. The marine Upper Bowland Shales are at the base and rest conformably on the Lower Bowland Shales (Lower Carboniferous). Together with the succeeding Bowland Grit Group, 1200 feet thick, they make up the Pendleian Stage (E 1 ). The E. bisulcatum marine band marks the base of the Arnsbergian (E 2 ) and is followed by the Roeburndale Grit Group, 600 feet thick, which is in turn succeeded by the important Caton Shales ( Ct. nitidus Zone). The upper part of the sequence is much thinner than in other areas. The Sabdenian (H) has but one marine band ( H. beyrichianum ) and a succeeding thin sandstone. The Kinderscoutian (R 1 ) starts with brachiopod beds, follows with two Reticuloceras marine bands and has red sandstones near the top. The Marsdenian (R 2 ), with R. gracile at the base, has similar red sandstones, whilst the Yeadonian (G 1 ), only exposed farther north in the Greta valley, contains the G. cancellatum and G. cumbriense marine bands. The structure consists of a broad asymmetric synclinal area with steep dips on the flanks and gentle northerly dips in the axial regions. The dominant trend of the faults is north-westerly and the downthrows south-westerly.